mars research paper introduction

• DOI: 10.1017/CBO9780511536069.011
• Corpus ID: 124108379

Mars: An Introduction to its Interior, Surface and Atmosphere: References

• Nadine Barlow , Fran Bagenal , +5 authors Sara Russell
• Published 2008
• Geology, Environmental Science, Physics

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Mars exploration on the move.

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Mu-ming Poo, Mars exploration on the move, National Science Review , Volume 7, Issue 9, September 2020, Page 1413, https://doi.org/10.1093/nsr/nwaa181

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While the world is still struggling to overcome the COVID-19 pandemic, a new round of Mars exploration proceeded as planned, catching the July–August 2020 window of Earth–Mars close proximity that occurs once every 26 months. The excitement began with United Arab Emirates’ launch of the  Hope orbiter on 19 July, followed by China's launch of the Tianwen 1 (天问一号) explorer on 23 July, and NASA’s launch of the Perseverance rover on 30 July. All these probes will reach the vicinity of Mars seven months later. The successful launch of Emirates’ Hope orbiter and China's Tianwen 1 explorer into the Earth-to-Mars Hohmann transfer orbit marks the beginning of Mars exploration by these two countries, whereas the launch of NASA’s Perseverance rover is the continuation of a long series of Mars missions of the US that began in 1964.

The Emirates’ Hope orbiter was built through a collaboration between Mohammed bin Rashid Space Center in United Arab Emirates and three US universities, and it was launched at Tanegashima Island launch site using Japan's top-of-the-line H2A rocket. When it reaches Mars’ orbit, the probe will thoroughly investigate Mars’ atmosphere and weather events such as dust storms in the lower atmosphere. It will answer the questions of how and why the weather varies in different regions of Mars, and why Martian atmosphere is losing hydrogen and oxygen into space.

The Tianwen 1 Mars explorer, named after the title of a poem by the ancient Chinese poet Qu Yuan, ‘Questions to Heaven’, was launched at Wenchang launch site in Hainan Providence using China's most powerful ‘Long March 5’ (长征五号) carrier rocket. This is an ambitious ‘three steps in one’ attempt to combine circulating, landing and roving of Mars into one mission. The Tianwen 1 explorer includes an orbiter and a land explorer comprising an entry module and a rover, and it will perform exploration both in the orbit and on land, either independently or in coordination. The orbiter and rover carry a variety of cameras, detectors, spectrometers and particle analyzers to investigate the planet's ionosphere, magnetic field, geological structure, soil and mineral compositions, underground distribution of water/ice, and cosmic ray particles.

Perseverance is NASA’s fifth Mars rover, launched from Cape Canaveral Air Force Station in Florida using a United Launch Alliance Atlas V rocket. It is designed to search for astrobiological evidence of ancient microbial life on Mars. When it lands at Jezero Crater, the rover will gather rock and soil samples for future return to Earth and will investigate the planet's climate and geology and pave the way for future human exploration of Mars. Of particular interest is the light-weight Ingenuity Mars Helicopter that will be deployed by the rover for testing the feasibility of powered, controlled flight in the Martian atmosphere, whose density is only 1% that of the Earth. If Ingenuity's flight is successful, future robotic flying vehicles could offer unique low-altitude views of Mars not provided by orbiters and rovers.

Space exploration presents an ideal platform for inter-national collaboration. The best example is the International Space Station (ISS), participated in by 16 countries including Russia, US, Japan, Canada and Brazil and 11 member countries of the European Space Agency. Many scientific projects were carried out in the ISS, and the most notable one is the Alpha Magnetic Spectrometer (AMS) project led by Samuel C.C. Ting. On board ISS since 2011, AMS has collected a large amount of data on cosmic ray particles that may shed light on the nature of dark matter and antimatter. Seven Chinese research institutions have participated in the AMS international team, and the Chinese Academy of Sciences (CAS) Institute of Electrical Engineering, the Institute of High-Energy Physics, and China Academy of Launch Vehicle Technology have built a key component of ASS—a large permanent magnet, the largest example of such equipment ever shipped into space.

Understanding the mystery of the universe has been a dream of humanity ever since the dawn of civilization. Perhaps more than any other science, astronomy captures the imagination of all curious minds. Mars exploration signifies humanity's quest in the scientific frontier. It is often characterized in the media as a ‘space race’, linked to the technological competition among superpowers, but it should really be a race in the Olympian spirit. We will all get to the finishing line and share the excitement and achievement together, as exemplified by the memorable scenes of multinational astronauts working together in the confined space of the ISS. Sometime in the distant future, a space station will appear on Mars as an extension of the harmonious global village, where people of all nations and races will work together to fulfill the dream of humankind.

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Introduction: A New Chapter in Mars Research

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• Reinald Kallenbach 3 ,
• Johannes Geiss 3 &
• William K. Hartmann 4  

Part of the book series: Space Sciences Series of ISSI ((SSSI,volume 12))

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This book reviews the most recent progress in constraining the timescales and geological processes in the evolution of Mars. It developed from a series of workshops on planetary science at the International Space Science Institute (ISSI), in Bern. The first of these meetings in February, 1999, concentrated on the interdisciplinary assessment of the astronomical, chronological, and geochemical constraints of the formation of the inner solar Esystem ~4.56 Gyr ago (Benz et al. , 2000). It appeared natural to continue with a core group meeting, reviewing the knowledge on the subsequent chronology of the inner solar system until the present day on the exemplary cases of Mars and Moon. Among the terrestrial planets, Mars is unique to have undergone all planetary evolutionary steps, without global resets, till the present (Encrenaz et al. , 1995; Bibring and Erard, 2001). The discussion on the “red planet” climaxed with a workshop on Chronology and Evolution of Mars in April, 2000, emphasizing communication and collaboration between the geochemical dating community, the crater chronologists, and the photogeologists.

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Mars and the ESA Science Programme - the case for Mars polar science

Introduction

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Kallenbach, R., Geiss, J., Hartmann, W.K. (2001). Introduction: A New Chapter in Mars Research. In: Kallenbach, R., Geiss, J., Hartmann, W.K. (eds) Chronology and Evolution of Mars. Space Sciences Series of ISSI, vol 12. Springer, Dordrecht. https://doi.org/10.1007/978-94-017-1035-0_1

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Habitability of mars: how welcoming are the surface and subsurface to life on the red planet.

1. Introduction

2. characteristics of the martian surface and subsurface, 2.1. habitability of the martian surface, 2.1.1. ice and water, 2.1.2. organic compounds, 2.1.3. salts, 2.1.4. radiation, 2.1.5. atmosphere, 2.2. mars subsurface as a potential habitat for life, 3. mars analog sites on earth, 3.1. dry valleys of antarctica, 3.2. atacama desert, 3.3. lava tubes, 4. studies on survival of organisms in simulated martian conditions, 4.1. microorganisms, 4.1.1. archaea, 4.1.2. bacteria, martian soil analogue exposure, exposure of bacterial isolates from spacecraft assembly facilities, survival of bacteria in brines, conclusions on growth of bacteria under martian conditions, 4.1.3. fungi, 4.2. lichens, 4.3. bryophytes, 5. considerations for future studies, 6. conclusions, author contributions, conflicts of interest.

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Share and Cite

Checinska Sielaff, A.; Smith, S.A. Habitability of Mars: How Welcoming Are the Surface and Subsurface to Life on the Red Planet? Geosciences 2019 , 9 , 361. https://doi.org/10.3390/geosciences9090361

Checinska Sielaff A, Smith SA. Habitability of Mars: How Welcoming Are the Surface and Subsurface to Life on the Red Planet? Geosciences . 2019; 9(9):361. https://doi.org/10.3390/geosciences9090361

Checinska Sielaff, Aleksandra, and Stephanie A. Smith. 2019. "Habitability of Mars: How Welcoming Are the Surface and Subsurface to Life on the Red Planet?" Geosciences 9, no. 9: 361. https://doi.org/10.3390/geosciences9090361

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Introduction: A New Chapter in Mars Research

2001, Space Sciences Series of ISSI

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An Origin of Life on Mars

Evidence of past liquid water on the surface of Mars suggests that this world once had habitable conditions and leads to the question of life. If there was life on Mars, it would be interesting to determine if it represented a separate origin from life on Earth. To determine the biochemistry and genetics of life on Mars requires that we have access to an organism or the biological remains of one—possibly preserved in ancient permafrost. A way to determine if organic material found on Mars represents the remains of an alien biological system could be based on the observation that biological systems select certain organic molecules over others that are chemically similar (e.g., chirality in amino acids).

Organic molecules derived from life on Mars could remain in ancient permafrost. Anomalies such as the prevalence of molecules of a certain chirality would be tell-tale signs of alien life.

MARS AND A SECOND GENESIS OF LIFE

Mars today is a cold dry desert world with surface conditions that are not habitable even for the hardiest life forms from Earth. The average surface temperature is −60°C and the atmospheric pressure is near the triple point of water: 120 times lower than sea level pressure on Earth. Even worse for habitability, solar ultraviolet light at wavelengths down to 190 nm penetrates to the surface. Although there is ample evidence for H 2 O on Mars, there has been no direct observation of liquid water: only ice, vapor, and geomorphological traces of the action of past liquid water.

In spite of the harshness of the present Martian environment, the Red Planet is a prime target for astrobiology. The motivation for the search for life on Mars comes from the evidence of past water activity. Figure 1 shows an image of Nanedi Vallis, which is perhaps the best example of the long-term flow of liquid water on Mars ( Malin and Carr 1999 ). The canyon is about 2 km across and shows a sinuous pattern consistent with slow erosive fluid flow. The canyon is probably not the actual riverbed. Instead, the bed of the river that carved the canyon is visible in the upper portion of the image. The small size of the riverbed compared to the large canyon indicates that the liquid flowed for a long period of time—although not necessarily continuously. Other fluids suggested as possible geological agents on Mars include wind, glacial ice, lava, and liquefied CO 2 . Liquid water, flowing repeatedly and stably on the surface, best explains the features seen in Figure 1 .

Liquid water on another world. Mars Global Surveyor image showing Nanedi Vallis in the Xanthe Terra region of Mars. Image covers an area 9.8 km by 18.5 km; the canyon is about 2.5 km wide. This image is the best evidence we have of liquid water on Mars. Photo from NASA/Malin Space Sciences.

It is useful to more carefully consider what we are searching for on Mars. Until recently, it was assumed that if there ever were life on Mars, it would necessarily represent a second genesis—a different origin from life on Earth. However, it is now known that many of the meteorites found on Earth have come from Mars ( McSween 1984 ). Furthermore, studies of the magnetic domains within one of these meteorites by Weiss et al. (2000) have shown that interior temperatures never exceed the survival limits of microorganisms. Thus, it is necessary to consider the possibility that life from Mars was carried to Earth and it is possible that life from Earth could have similarly been carried to Mars—although this path may be less probable. This implies that the discovery of life on Mars does not automatically mean the discovery of a second genesis. To demonstrate a second genesis, it will be necessary to show that Martian life is not related to Earth life.

The search for a second example of life is a key goal for astrobiology. All life on Earth shares common biochemistry and descends from a common ancestor. This prevents us from understanding which aspects of biochemistry and genetics are essential features of life and which are merely particular to the evolutionary history of life on this planet. To develop a more general understanding of life, we need more than one example. Hence, we hope that Mars may have been the site of an independent origin of life.

To determine if life on Mars represents a second type of life requires that we study biological material: Fossils are not enough. Mineralized fossils or tracks of life would be proof of life on Mars, but would not inform us about the relationship of that life to Earth’s life. To determine that relationship, we need to study the genetic material and biochemical structure of Martian life—something that can only be done on organisms—alive or dead. We would be convinced of a shared origin of life if Mars had the same chirality, choice of amino acids, genetic code, choice of lipids, and so on. If any or all of these were substantially different, we might conclude a separate origin.

THE ORIGIN OF LIFE: WHAT WE KNOW FROM EARTH THAT APPLIES TO MARS

Everything we know about biology we have learned by studying the single example of life on Earth. The nature of life and its early history inform our search for life on Mars, and elsewhere in the universe. The earliest firm evidence for life on Earth dates back 3.5 billion years ago and is in the form of fossil microbial mats ( Tice and Lowe 2004 ; Allwood et al. 2006 ). There are also chemical signatures consistent with life in rocks that are 3.8 billion years old ( Schidlowski 1988 ; Abramov and Mojzsis 2009 ). The appearance of life on Earth was soon after the end of the late heavy bombardment ( Abramov and Mojzsis 2009 ), suggesting that it appeared as soon as conditions on the surface of the Earth became able to support liquid water environments.

Although the early appearance of life on Earth seems certain, how life originated on Earth remains unclear, with multiple hypotheses competing for attention. Nonetheless, all the scenarios suggested for the origin of life on early Earth can be reviewed for their applicability to early Mars. Figure 2 shows a diagram of the published proposals for the origin of life on Earth ( Davis and McKay 1996 ).

Diagram of the proposed explanations for the origins of life on Earth. Any of these explanations would work on Mars as well as on Earth. From Davis and McKay (1996) .

The first divide between the proposals for how life first appeared on the Earth is between those postulating that life arose independently on Earth and those that postulate that life was carried to Earth from elsewhere. If life arose on Earth, the next logical division is between an organic and inorganic nature for that early life. Further divisions within the organic origin of life relate to the nature of the energy source and metabolism for the first organism. How can these ideas be applied to a possible origin of life on Mars? First, what all have in common is a requirement for liquid water environments—the common thread for life today as well as for its origins. Second, all the scenarios listed in Figure 2 could apply to Mars. This is hardly surprising since our understanding of the environment on early Mars suggests that it had a range of environments similar to those on early Earth. Thus, whatever specific conditions and environments led to life on Earth were probably present on Mars as well.

An interesting contrast between Earth and Mars with respect to the origin of life is that the record of early events may be better preserved on Mars than on Earth. The very processes that maintain the habitability of Earth have virtually destroyed the evidence of the first traces of life. Thus, if present on both Earth and Mars sometime before 3.8 billion years ago, the best place to search for physical evidence of the steps that lead to life may be on Mars.

SEARCHING FOR EVIDENCE OF A SECOND GENESIS OF LIFE ON MARS

There are several possible places on Mars where we might find evidence of life that can be used to determine if it emerged as a second genesis. Possible targets include: (1) Life in the surface soil, (2) Life in subsurface liquid water, (3) Organisms, probably dead, but preserved in ancient salt or mineral deposits, and (4) Organisms, dead or alive, preserved in ancient ice. Ancient ice is the most promising target known at this time ( Smith and McKay 2005 ), but before discussing this in more detail, it is interesting to first briefly review the case for the other possibilities.

It is unlikely that the surface soil on Mars, such as sampled by the Viking biology experiments, contain life. The general view of the results of the Viking biology experiment is that there is no life present and the reactivity detected was due to chemical processes ( Klein 1999 ). However, the results of the Labeled Release experiment still invoke speculations that the reactions seen were based on biology ( Levin 2007 ; Levin and Straat 1981 ). If the surface is inhospitable, many have suggested ( Boston et al. 1992 ) that the subsurface may hold liquid water aquifers that support chemosynthetic life. However, there is as yet no direct evidence of subsurface liquid water. On Earth, the oldest biochemical remains of life are found in ancient amber ( Cano and Burucki 1995 ) and salt deposits ( Vreeland et al. 2000 ). However, in both cases, the antiquity of the life found in these deposits is questioned ( Willerslev and Cooper 2005 ). Although amber—a product of trees—is not expected on Mars, if ancient mineral or salt deposits are found, they should be investigated.

Ancient ice presents a known environment on Mars that may contain the frozen remains of life in an accessible form. Smith and McKay (2005) have suggested that the ancient cratered terrain in the southern highlands of Mars near 80°S, 180°W would be an ideal target. The map of Mars ( Fig. 3 ) shows crater distribution, ground ice, and crustal magnetism on Mars. Each green circle represents a crater with a diameter greater than 15 km based on the crater distribution in Barlow (1997) . The filled green circles are volcanic craters. The boundary between the smooth northern plains and the cratered southern highlands is shown with a green line. The southern regions of Mars are more heavily cratered and therefore considered to be older. The solid blue lines in Figure 4 show the extent of near surface ground ice as determined by the Odyssey mission ( Feldman et al. 2002 ). Ground ice is present near the surface polarward of these lines. Crater morphology indicates deep ground ice poleward of 30° ( Squyres and Carr 1986 ), shown here by dark blue lines and arrows. Also shown on this figure is the crustal magnetism discovered by Acuña et al. (1999) . The crustal magnetism is shown as red for positive and blue for negative. Full scale is 1500 nT. The typical strength of Earth’s magnetic field at the surface is 50,000 nT. The crustal magnetism is thought to have formed very early in Mars’ history, more than 4.5 Gyr ago. The fact of crustal magnetism implies that these surfaces have not been severely heated or shocked. The region between 60° and 80°S at 180°W is heavily cratered, preserves crustal magnetism, and has ground ice present. This is the suggested target site for drilling to find the frozen remains of ancient Martian life.

Maps showing crater distribution, ground ice, and crustal magnetism on Mars. The suggested target site for deep drilling to search for evidence of ancient life on Mars is the region between 60° and 80°S at 180°W, where the ground is heavily cratered, crustal magnetism is preserved, and ground ice is present. Figure from Smith and McKay (2005) .

Conceptual comparison of the distribution of molecules in organic matter of biological and nonbiological origin. The ordinate “type of molecule” represents in a general way the size, structure, chirality, and all other features of the molecule. Nonbiological processes produce uniform distributions of organic material, illustrated here by the curve. Biology, in contrast, selects and uses only a few distinct molecules, shown here as spikes (e.g., the 20 l -amino acids on Earth). Alien life might have similar selectivity but based on a different set of molecules ( McKay 2004 ).

DETECTING MARTIAN LIFE

It may be possible that a mission to Mars, landing in the southern highlands and drilling deeply below the surface, would find organic rich sediments that date back to ancient times when conditions on Mars could have supported widespread life. The challenge then would be to determine if this organic material was of biological origin. We know that there is organic material of nonbiological origin in asteroids, comets, and throughout the outer solar system, so organic material from the deep core on Mars could also be nonbiological.

There are two related questions here: First, is this organic material of biological origin, and second, if it is of biological origin, is it evidence of a second genesis of life? If the organic material pulled from a deep ice core on Mars is derived from biochemistry identical to Earth life, then it should be relatively straightforward to show that it is of biological origin. The technology for direct detection of DNA, RNA, ATP, and other key molecules associated with life on Earth has proceeded to the point that it could easily detect the remains of Earth-like life. These molecules would be preserved over the ages by the low temperatures ( Kanavarioti and Mancinelli 1990 ).

The more difficult, but much more interesting case, is that in which the organic material from Mars is of biological origin but does not have the biomolecules associated with Earth life. In this case, our specialized biochemical tools for detecting life are ineffective.

A possible approach to recognizing alien biology has been suggested by McKay (2004) as the “lego” principle. This is the observation that life, like legos, is based on the repeated use of a small number of building blocks. For legos, the building blocks are small plastic interlocking blocks of a few sizes and shapes. Many different structures can be assembled from these blocks. For life on Earth, the building blocks are the 20 amino acids, the bases A, T, C, G, and U in DNA and RNA, the sugars, and a few fatty acids (see, e.g., Lehninger 1975 , page 27).

The lego principle can form the basis of a search for biological origins due to the contrast between the selectivity of biology and the nonselectivity of chemistry. A detailed analysis of organic compounds of nonbiological origin would show that a wide range of organic material is present and that their relative concentrations would be determined by their chemical properties. For organic material of biological origin, the distribution would be a series of spikes. In particular, the concentration of chemically identical molecules might be orders of magnitude different in a biological sample, whereas similar in a chemical sample. An example of this is the biological selection of L versus D amino acids for proteins by life on Earth. This concept is presented schematically in Figure 4 , which shows the concentration of organic molecules as a function of the type of molecule. The nonbiological distribution is smooth, as seen for example in the Murchison carbonaceous meteorite, whereas the biological distribution is a series of spikes ( McKay 2004 ).

Even if an organism dies, the spiked distribution of organic molecules will persist for some time. However, the chemical distribution in Figure 3 is of higher entropy than the biological distribution, and hence over time, as chemical bonds are broken and reformed, this biological signature will be erased and become indistinguishable from the chemical distribution. Two processes cause this decay: thermal alteration and ionizing radiation. For Mars, the low temperatures in the polar ice ensures that thermal alteration is slow compared to the age of the planet ( Kanavarioti and Mancinelli 1990 ). Ionizing radiation is not temperature dependent. Low but continuous radiation from crustal abundances of U, Th, and K will eventually kill any frozen organism, but will not completely destroy the biological signature of buried frozen organics on Mars ( Smith and McKay 2005 ).

If the organics from Mars show a spiked pattern that is distinct but different from the pattern for Earth life, then this should be both evidence of life and evidence of a second genesis. This is shown schematically in Figure 4 by the red lines. The lego principle thus provides an approach to searching for life that is general enough to detect a second genesis—albeit of carbon-based water-based life. Such life is what we expect to find on Mars and would be a significant first step.

It is not clear how to actually do the measurements illustrated in Figure 4 . Currently, the standard approach would be based on GC-MS (gas chromatography-mass spectrometry) with a suitable extraction method. This is, in fact, what was flown to Mars on Viking. However, new methods for organic detection, such as lab-on-a-chip methods, Raman spectroscopy, and UV fluorescence, should also be considered. Analysis of natural soil with low organic content such as the soils of the Atacama Desert ( Navarro-Gonzalez et al. 2003 , 2006 ) provide a way to select the most useful methods. Life, or at least its remains, may be out there waiting for us to find it.

It is important to add that even a null result in the search for life on Mars would be informative. It might show that the origin of life is a matter of chance, and the window of opportunity simply was not long enough for life to begin on Mars. Alternatively, it might show that conditions on Mars were too salty, too acid, etc., and inhibited the self-assembly processes required for the origin of life. Finally, we may discover that the origin of life required a fairly specific energy source, mineral, or nutrient (e.g., nitrogen) that was inadequate or absent on Mars. Such insights, even if negative, would help us understand how general the origin of life might be.

The search for life on Mars may be our first chance to discover a second example of life and to investigate the biochemical properties of that life. This possibility is of fundamental importance from both a philosophical and science point of view. Determining where to look and how to search for evidence of a second genesis on Mars is therefore a key task for astrobiology in the next decade.

Editors: David Deamer and Jack W. Szostak

Additional Perspectives on The Origins of Life available at www.cshperspectives.org

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Mars is the fourth planet from the Sun, and the seventh largest. It’s the only planet we know of inhabited entirely by robots.

Mission Status

Nasa spacecraft in orbit, nasa rovers on the surface, featured topics.

How Curiosity’s Sky Crane Changed the Way NASA Explores Mars

Twelve years ago, NASA landed its six-wheeled science lab using a daring new technology.

How Do We Land on Mars?

It's complicated. Read on to find out how it's done.

A Fascinating Mars Rock

The most puzzling, complex, and potentially important rock yet investigated by Perseverance.

What is a Potential Biosignature?

Scientist Lindsay Hays explains what defines potential signs of ancient life on other worlds

Curiosity Discovers a Surprise

The rover found rocks made of pure sulfur--a first.

Mars Overview

Mars is no place for the faint-hearted. It’s dry, rocky, and bitter cold. The fourth planet from the Sun, Mars, is one of Earth's two closest planetary neighbors (Venus is the other). Mars is one of the easiest planets to spot in the night sky – it looks like a bright red point of light.

Despite being inhospitable to humans, robotic explorers – like NASA's Perseverance rover – are serving as pathfinders to eventually get humans to the surface of the Red Planet.

JUly 25, 2024

NASA’s Perseverance Rover Scientists Find Intriguing Mars Rock

The six-wheeled geologist found a fascinating rock that has some indications it may have hosted microbial life billions of years ago, but further research is needed.

Why Do We Go?

Mars is one of the most explored bodies in our solar system, and it's the only planet where we've sent rovers to explore the alien landscape. NASA missions have found lots of evidence that Mars was much wetter and warmer, with a thicker atmosphere, billions of years ago.

Mars Relay Network: Interplanetary Internet

How we explore.

Mars Sample Return

NASA and ESA (European Space Agency) are planning ways to bring the first samples of Mars material back to Earth for detailed study. 

Mars Perseverance Rover (Mars 2020)

The Mars 2020 mission Perseverance rover is the first step of a proposed roundtrip journey to return Mars samples to Earth.

Mars Curiosity Rover (Mars Science Laboratory)

Curiosity is investigating Mars to determine whether the Red Planet was ever habitable to microbial life.

The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission is the first mission devoted to understanding the Martian upper atmosphere.

Mars Reconnaissance Orbiter

Mars Reconnaissance Orbiter searches for evidence that water persisted on the surface of Mars for a long period of time.

Mars Odyssey

Mars Odyssey mission created the first global map of chemical elements and minerals that make up the Martian surface.

Mars Resources

View the one-stop shop for all Mars iconic images, videos, and more!

News & Features

Here’s How Curiosity’s Sky Crane Changed the Way NASA Explores Mars

NASA Trains Machine Learning Algorithm for Mars Sample Analysis

NASA Invites Media, Public to Attend Deep Space Food Challenge Finale

UPDATED: 10 Things for Mars 10

Beyond the Moon

Humans to mars.

Like the Moon, Mars is a rich destination for scientific discovery and a driver of technologies that will enable humans to travel and explore far from Earth.

Mars remains our horizon goal for human exploration because it is one of the only other places we know in the solar system where life may have existed. What we learn about the Red Planet will tell us more about our Earth’s past and future, and may help answer whether life exists beyond our home planet.

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Articles on Life on Mars

Displaying 1 - 20 of 43 articles.

The Mars Sample Return mission has a shaky future, and NASA is calling on private companies for backup

Chris Impey , University of Arizona

NASA’s search for life on Mars: a rocky road for its rovers, a long slog for scientists – and back on Earth, a battle of the budget

Amy J. Williams , University of Florida

For All Mankind’s Happy Valley: why a Martian city could well extend below the surface

Elizabeth Stanway , University of Warwick

Could people breathe the air on Mars?

Phylindia Gant , University of Florida and Amy J. Williams , University of Florida

As the Perseverance rover lands on Mars, there’s a lot we already know about the red planet from meteorites found on Earth

James Scott , University of Otago

Perseverance Mars rover: how to prove whether there’s life on the red planet

Samantha Rolfe , University of Hertfordshire

Mars: Perseverance rover set for nail-biting landing – here’s the rocket science

Andrew Coates , UCL

As new probes reach Mars, here’s what we know so far from trips to the red planet

Tanya Hill , Museums Victoria Research Institute

How to get people from Earth to Mars and safely back again

Chris James , The University of Queensland

Mars: mounting evidence for subglacial lakes, but could they really host life?

David Rothery , The Open University

Perseverance: the Mars rover searching for ancient life, and the Aussie scientists who helped build it

David Flannery , Queensland University of Technology

NASA’s big move to search for life on Mars – and to bring rocks home

Briony Horgan , Purdue University and Melissa Rice , Western Washington University

Meteorites from Mars contain clues about the red planet’s geology

Arya Udry , University of Nevada, Las Vegas

Spotting alien life – how ‘microfossils’ can fool scientists

Alexander Brasier , University of Aberdeen

Tiny specks in space could be the key to finding martian life

Andrew Tomkins , Monash University

Tardigrades: we’re now polluting the moon with near indestructible little creatures

Monica Grady , The Open University

Why the idea of alien life now seems inevitable and possibly imminent

Cathal D. O'Connell , The University of Melbourne

Our long fascination with the journey to Mars

Paulo de Souza , CSIRO

Colonizing Mars means contaminating Mars – and never knowing for sure if it had its own native life

David Weintraub , Vanderbilt University

Sorry Elon Musk, but it’s now clear that colonising Mars is unlikely – and a bad idea

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Mars – the fourth planet from the Sun – is a dusty, cold, desert world with a very thin atmosphere. This dynamic planet has seasons, polar ice caps, extinct volcanoes, canyons and weather.

Introduction

Mars is one of the most explored bodies in our solar system, and it's the only planet where we've sent rovers to roam the alien landscape. NASA missions have found lots of evidence that Mars was much wetter and warmer, with a thicker atmosphere, billions of years ago.

Mars was named by the Romans for their god of war because its reddish color was reminiscent of blood. The Egyptians called it "Her Desher," meaning "the red one."

Even today, it is frequently called the "Red Planet" because iron minerals in the Martian dirt oxidize, or rust, causing the surface to look red.

Mars was named by the ancient Romans for their god of war because its reddish color was reminiscent of blood. Other civilizations also named the planet for this attribute – for example, the Egyptians called it "Her Desher," meaning "the red one." Even today, it is frequently called the "Red Planet" because iron minerals in the Martian dirt oxidize, or rust, causing the surface to look red.

Potential for Life

Scientists don't expect to find living things currently thriving on Mars. Instead, they're looking for signs of life that existed long ago, when Mars was warmer and covered with water.

Size and Distance

With a radius of 2,106 miles (3,390 kilometers), Mars is about half the size of Earth. If Earth were the size of a nickel, Mars would be about as big as a raspberry.

From an average distance of 142 million miles (228 million kilometers), Mars is 1.5 astronomical units away from the Sun. One astronomical unit (abbreviated as AU), is the distance from the Sun to Earth. From this distance, it takes sunlight 13 minutes to travel from the Sun to Mars.

Orbit and Rotation

As Mars orbits the Sun, it completes one rotation every 24.6 hours, which is very similar to one day on Earth (23.9 hours). Martian days are called sols – short for "solar day." A year on Mars lasts 669.6 sols, which is the same as 687 Earth days.

Mars' axis of rotation is tilted 25 degrees with respect to the plane of its orbit around the Sun. This is another similarity with Earth, which has an axial tilt of 23.4 degrees. Like Earth, Mars has distinct seasons, but they last longer than seasons here on Earth since Mars takes longer to orbit the Sun (because it's farther away). And while here on Earth the seasons are evenly spread over the year, lasting 3 months (or one quarter of a year), on Mars the seasons vary in length because of Mars' elliptical, egg-shaped orbit around the Sun.

Spring in the northern hemisphere (autumn in the southern) is the longest season at 194 sols. Autumn in the northern hemisphere (spring in the southern) is the shortest at 142 days. Northern winter/southern summer is 154 sols, and northern summer/southern winter is 178 sols.

Mars has two small moons, Phobos and Deimos , that may be captured asteroids. They're potato-shaped because they have too little mass for gravity to make them spherical.

The moons get their names from the horses that pulled the chariot of the Greek god of war, Ares.

Phobos, the innermost and larger moon, is heavily cratered, with deep grooves on its surface. It is slowly moving towards Mars and will crash into the planet or break apart in about 50 million years.

Deimos is about half as big as Phobos and orbits two and a half times farther away from Mars. Oddly-shaped Deimos is covered in loose dirt that often fills the craters on its surface, making it appear smoother than pockmarked Phobos.

Go farther. Explore the Moons of Mars ›

Mars has no rings. However, in 50 million years when Phobos crashes into Mars or breaks apart, it could create a dusty ring around the Red Planet.

When the solar system settled into its current layout about 4.5 billion years ago, Mars formed when gravity pulled swirling gas and dust in to become the fourth planet from the Sun. Mars is about half the size of Earth, and like its fellow terrestrial planets, it has a central core, a rocky mantle, and a solid crust.

Mars has a dense core at its center between 930 and 1,300 miles (1,500 to 2,100 kilometers) in radius. It's made of iron, nickel, and sulfur. Surrounding the core is a rocky mantle between 770 and 1,170 miles (1,240 to 1,880 kilometers) thick, and above that, a crust made of iron, magnesium, aluminum, calcium, and potassium. This crust is between 6 and 30 miles (10 to 50 kilometers) deep.

The Red Planet is actually many colors. At the surface, we see colors such as brown, gold, and tan. The reason Mars looks reddish is due to oxidization – or rusting – of iron in the rocks, regolith (Martian “soil”), and dust of Mars. This dust gets kicked up into the atmosphere and from a distance makes the planet appear mostly red.

Interestingly, while Mars is about half the diameter of Earth, its surface has nearly the same area as Earth’s dry land. Its volcanoes, impact craters, crustal movement, and atmospheric conditions such as dust storms have altered the landscape of Mars over many years, creating some of the solar system's most interesting topographical features.

A large canyon system called Valles Marineris is long enough to stretch from California to New York – more than 3,000 miles (4,800 kilometers). This Martian canyon is 200 miles (320 kilometers) at its widest and 4.3 miles (7 kilometers) at its deepest. That's about 10 times the size of Earth's Grand Canyon .

Mars is home to the largest volcano in the solar system, Olympus Mons. It's three times taller than Earth's Mt. Everest with a base the size of the state of New Mexico.

Mars appears to have had a watery past, with ancient river valley networks, deltas, and lakebeds, as well as rocks and minerals on the surface that could only have formed in liquid water. Some features suggest that Mars experienced huge floods about 3.5 billion years ago.

There is water on Mars today, but the Martian atmosphere is too thin for liquid water to exist for long on the surface. Today, water on Mars is found in the form of water-ice just under the surface in the polar regions as well as in briny (salty) water, which seasonally flows down some hillsides and crater walls.

Mars has a thin atmosphere made up mostly of carbon dioxide, nitrogen, and argon gases. To our eyes, the sky would be hazy and red because of suspended dust instead of the familiar blue tint we see on Earth. Mars' sparse atmosphere doesn't offer much protection from impacts by such objects as meteorites, asteroids, and comets.

The temperature on Mars can be as high as 70 degrees Fahrenheit (20 degrees Celsius) or as low as about -225 degrees Fahrenheit (-153 degrees Celsius). And because the atmosphere is so thin, heat from the Sun easily escapes this planet. If you were to stand on the surface of Mars on the equator at noon, it would feel like spring at your feet (75 degrees Fahrenheit or 24 degrees Celsius) and winter at your head (32 degrees Fahrenheit or 0 degrees Celsius).

Occasionally, winds on Mars are strong enough to create dust storms that cover much of the planet. After such storms, it can be months before all of the dust settles.

Magnetosphere

Mars has no global magnetic field today, but areas of the Martian crust in the southern hemisphere are highly magnetized, indicating traces of a magnetic field from 4 billion years ago.

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Mars Sample Return

Mars 2020: Perseverance Rover

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Mars: The Exploration of the Red Planet Research Paper

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Introduction

Mars, the fourth planet in order of increasing distance from the sun and the first beyond the earth’s orbit. Under favorable conditions, it appears in the night sky as a yellowish red object (hence the name “red planet”) of the first magnitude. Mars has long fascinated us because of its many similarities to the earth and because of the possibility that life might exist there. The flyby of the crewless spacecraft Mariner 4 past the planet in 1965 started an era of intense exploration that still continues. Following several crewless flybys and orbiters launched by the United States (Mariners 4, 6, 7, and 9) and by the Soviet Union (Mars 3, 4, 5, and 6), the first successful soft landing of a spacecraft on another planet was achieved on July 20, 1976, when the U.S. spacecraft Viking 1 landed on the surface of Mars. Since then, Mars has been visited by several unpiloted craft, including the Mars Pathfinder spacecraft in 1997 and the Mars Global Surveyor from 1997 to 2006. (Squyres, 12) When images from these two probes were compared, scientists began to suspect that water had once flowed at several locations. Since 2004, NASA’s (National Aeronautics and Space Administration’s) Mars Exploration Rovers twin robot-geologists Spirit and Opportunity have explored the harsh Martian environment in search of water. The Phoenix Mars Lander, which safely reached the planet’s the North Pole in 2008, will analyze the icy soil for evidence of past microbial life. Mars is now perceived as a planet of spectacularly diverse topography with huge volcanoes, deep canyons, dry riverbeds, and extensive sand seas. While evidence of life there continues to be elusive, Mars remains interesting for geologic, chemical, and meteorological comparisons with the earth (Paolo, p.89).

Telescopic Observations

Following the first telescopic observations of Mars by Galileo in 1610, the planet has been observed continually, with changes in its appearance noted and mapped. Mars is too distant for any surface relief to be discerned through the telescope. All that is seen are bright and dark markings, which may be in the atmosphere or on the surface. Most surface markings are in the equatorial regions, where various dark features contrast with the light areas or “deserts.” The shape and size of most markings change both seasonally and, slowly, over many years. Despite the many changes, the most prominent features are recognizable even on the earliest maps. The markings show poor correlation with topographic features revealed by spacecraft observations. Most are thought to result from thin deposits of windblown debris whose distribution changes with time. Bright polar caps are clearly visible through the telescope, and the larger size of the northern polar cap long has been recognized.

Most of the changes in appearance through the telescope are due to atmospheric effects of various kinds. Large arrays of white clouds commonly form in the middle latitudes and may persist for weeks. Those around the volcanic centers of Tharsis and Elysium most likely form when the air cools as it rises over the high volcanic regions. Other white clouds probably are caused by the daily recycling of water between the soil and the lower atmosphere. Frontal clouds and standing-wave clouds, seen clearly in spacecraft pictures, are probably not visible from the earth. During the fall thick clouds gather in the high latitudes to form polar hoods, which mask the growth of the polar caps. Brightening at the poles in this season is probably the result of both these clouds and the cap itself. Brightening in low areas such as Hellas and Argyre may also result from a combination of surface frost and clouds.

Whereas white clouds generally are brightest when observed in blue light, yellow clouds are brightest in yellow and orange. Yellow clouds occur mostly in the mid-southern latitudes at midsummer when large lateral and vertical temperature gradients cause extreme turbulence, which lifts large amounts of dust into the atmosphere. Activity generally starts in the region 320° W to 30° W and 30° S to 60° S and in most years spreads widely, so that ultimately the whole planet is engulfed in a gigantic dust storm. After the midsummer turbulence declines, dust slowly settles out of the atmosphere and the surface markings reappear. Global dust storms of this type were observed close up in 1971 by the Mariner 9 flyby space probe and in 1977 by the Viking orbiters (Squyres, p. 32).

No other aspect of Mars has aroused such widespread interest and controversy as the so-called canals. The controversy started in 1877 with the Italian astronomer Giovanni Schiaparelli’s publication of a map of Mars that showed many dark lines on the surface. These he called Canali, the Italian word for both “canal” and “channel.” In the ensuing decades, Mars observers were divided between those who claimed the canals existed and those who claimed they did not. The strongest proponent of the canals was the American astronomer Percival Lowell, who produced ever more intricate maps of linear markings based on observations at the observatory he founded in Flagstaff, Ariz. In a book published in 1908, he aroused considerable popular attention by suggesting that the markings were irrigation canals built by an advanced civilization. As better telescopes were built and instrumental measurements failed to confirm their existence, belief in the canals declined (Furniss, p. 68). The various space probes that have since visited Mars found no evidence for most of the lines on the early maps, with the result that most are now regarded as optical illusions.

Spacecraft Explorations

Most current knowledge of Mars is derived from space-probe observations, initially from the Mariner 9 and Viking missions. In 1965 the U.S. Mariner 4 flyby space probe returned the first close-up pictures of the planet, followed in 1969 by two additional flyby missions, Mariners 6 and 7. All three probes flew over the parts of the planet that most resemble the moon and presented a rather deceptive view of the planet as a moonlike body. The diverse geologic character of the Martian surface was not fully recognized until 1971. During that year Mariner 9 and two Soviet spacecraft, Mars 2 and 3, were placed in orbit around Mars. The Soviet spacecraft was short-lived, and their accompanying Landers failed to return useful data from the surface, but Mariner 9 continued to operate for a year, returning more than 7,000 pictures of the planet. (Paolo, 45) Additional photographs were obtained in 1974 by the Soviet vehicles Mars 4, 5, and 6. In 1976 two Viking spacecraft were placed in orbit around Mars, and two additional spacecraft landed on the surface. The Viking 2 and 1 orbiters continued to function, respectively, until 1978 and 1980, by which time they had taken over 50,000 pictures of the planet and returned a wealth of other data. Contact with the Viking 2 and 1 Landers was lost, respectively, in 1980 and 1982 (Squyres, p. 57).

After a 17-year hiatus in Mars exploration, the United States launched Mars Observer in 1992. Mission objectives were to study geology, geophysics, and climate of the red planet, but it ended in disappointment when contact was lost with the craft just before it entered Martian orbit. In 1996 Mars Pathfinder was launched to demonstrate that an unpiloted spacecraft could deliver and deploy a robotic rover. Not only was the mission a success, but also Pathfinder and its rover, Sojourner, returned unprecedented amounts of information including images, soil analyses, and wind measurements before their final data transmission in September 1997. The next two missions to Mars failed: Climate Orbiter burned up on entering Mars’s atmosphere in September 1999; and three months later Polar Lander and Deep Space 2 were lost on arrival.

These disappointments were followed by a spate of successes, beginning in 1997 when Mars Global Surveyor slipped into Martian orbit. For nine years the probe mapped the red planet returning dramatic evidence of hillside water flows before succumbing to battery failure in 2006. The Mars Odyssey spacecraft, launched in 2001, has captured more than 130,000 images and continues to transmit information about Martian geology, climate, and mineralogy. NASA joined with the European Space Agency and the Italian Space Agency for the Mars Express mission in 2003 (Paolo, p. 23). Despite losing Beagle 2, its land rover, Mars Express has provided information about various surface features, including buried impact craters, evidence of glacial activity, and the presence of methane gas. The pursuit of geological clues to the possibility of life on Mars continued with NASA’s land rovers Spirit and Opportunity, twin robotic vehicles that rolled off their airbag-encased Landers on opposite sides of Mars in 2004 (Furniss, p. 102). Sporting names selected from more than 10,000 entries in a student essay contest, the two solar-powered rovers have outlived their intended three-month mission and continue to transmit high-resolution, full-color images of Martian terrain, soil surfaces, and rocks. The Mars Reconnaissance Orbiter, launched in 2005, currently orbits high above the red planet, using a sounding device to search for subsurface water.

In May 2008 the Mars Reconnaissance Orbiter relayed photographs of the safe descent of the Phoenix Mars Lander as it parachuted onto the planet’s frozen North Pole. Daily instructions were sent from the earthbound control center, directing the Lander to collect soil samples from the icy surface. Phoenix used its robotic arm to deliver soil and ice samples to its onboard experiment platforms. The samples are to be analyzed in hopes of determining whether the location could have supported microbial life during the planet’s past.

General Physiography

Mars is markedly asymmetrical in the distribution of its surface features. Much of the Southern Hemisphere is heavily cratered like the lunar highlands and includes two large impact basins, Hellas and Argyre. In contrast, much of the Northern Hemisphere is covered with sparsely cratered plains. The planet has two major volcanic regions, the Tharsis region centered at 110° W on the equator and the Elysium region centered at 25° N, 212° W. Extending eastward from Tharsis are several large canyons that together makeup Valles Marineris, while east and north of the canyons are several huge dry riverbeds. The poles are distinctly different from the rest of the planet and appear to have thick deposits of layered sedimentary rocks exposed at the surface. The North Pole is also surrounded by extensive sand dunes.

Densely Cratered Terrain

This terrain is characterized by many large, relatively shallow craters; smooth intercrater plains; and a relatively small number of smaller craters (those less than 30 miles, or 50 km, in diameter). The terrain probably dates from very early in the planet’s history, possibly from 4 billion years ago, when the impact rate was higher than at present. The most extensive cratered areas are in the Southern Hemisphere. Fresh Martian craters differ markedly in appearance from those on the moon and Mercury. Most lunar craters are surrounded by disordered rubble-like ejecta that appears to have been deposited from ballistic trajectories. In contrast, the Martian craters are surrounded by ejecta that appears to have flowed along the ground. The fluid properties of the ejecta have been attributed to the presence in the Martian surface of large amounts of ground ice, which melts on impact and is incorporated into the ejecta. Crater examination by the Opportunity probe has revealed evidence of a watery and possibly habitable past on Mars.

Sparsely Cratered Plains

Plains cover much of the Northern Hemisphere and also occur within large impact basins such as Hellas and Argyre in the south. They are distinguished from the densely cratered terrain by the almost total absence of impact craters larger than 30 miles (50 km) in diameter. The plains have a different appearance in different areas. Around the large volcanoes in Tharsis and Elysium, the plains appear to be a thick succession of lava flows. In other areas, such as Chryse Planitia, where the Viking 1 spacecraft landed, the plains resemble those of the lunar maria, being relatively featureless except for impact craters and low winding ridges. These plains are probably also volcanic. The plains in the high northern latitudes have a variety of poorly understood features. Extensive areas have a polygonal fracture pattern, with individual polygons averaging 6 miles (10 km) across. In other areas are parallel linear markings, low escarpments, and intricate patterns of light and dark. Many of the unique characteristics of the northern plains have been attributed to repeated deposition and removal by the wind of layers of ice-rich debris. The number of impact craters on most of the plains, while considerably smaller than on the densely cratered terrain, is still sufficiently large to indicate an old age, probably in the range of 1 to 4 billion years. The only possible exceptions are the plains around the large volcanoes, which appear younger.

Volcanic and Tectonic Features

The large volcanoes of Tharsis are among the most spectacular features of the planet. The largest, Olympus Mons, is 15.5 miles (25 km) high and more than 340 miles (550 km) across at its base. Three other volcanoes in Tharsis reach approximately the same height. Each is topped by a central caldera, or crater, 50 to 75 miles (80 to 120 km) across, and on the flanks are numerous lava channels, lava tubes, flow fronts, and other features indicative of very fluid lava. Analysis of photographs transmitted by Odyssey in 2007 of the massive Arsia Mons volcano reveals seven black spots that scientists suspect are caves the size of football fields. If so, they would shield their contents from surface radiation and could potentially shelter life (Squyres, p. 78).

The style of volcanism on Mars is similar to that in Hawaii, except that the Martian features are ten times larger. The volcanoes are relatively young and may still be active. Tharsis is also the center of a set of fractures that occur over almost an entire hemisphere of the planet. They appear to have formed as a result of the loading of the crust by the Tharsis bulge.

Volcanoes also occur elsewhere on Mars, but they tend to be older and smaller than those in Tharsis. In 2007 the Spirit rover rolled onto evidence of an ancient volcanic explosion near its landing site dubbed “Home Plate” in Gusev Crater. Analysis revealed high chlorine content in the 2-meter- (6-foot) thick plateau of bedrock, suggesting that fluid basalt lava had come in contact with brine, indicating that water had been involved (Paolo, p. 59).

To the east of Tharsis and aligned along with the radial fractures are several enormous canyons. They stretch from the summit of the Tharsis bulge eastward for approximately 3,000 miles (5,000 km). Individual canyons are up to 125 miles (200 km) across and 1 to 4 miles (2 to 7 km) deep. The walls are steep and in many sections deeply gullied. In some parts, the walls have collapsed to form gigantic landslides several tens of miles across that have traveled more than 60 miles (100 km) along the canyon floor. The canyons are believed to have formed mainly by down faulting, followed by slumping and gullying of the walls (Furniss, p. 62).

Channels pose some of the more puzzling problems of Martian geology. Much of the densely cratered terrain is dissected by small channels that form drainage networks much like terrestrial river valleys. Liquid water, however,

• Furniss, Tim. The History of Space Exploration: And Its Future… Mercury Books London: 2005
• Paolo, Ulivi & Harland, David. Robotic Exploration of the Solar System. Springer Praxis Books: 2008
• Squyres, Steve. Roving Mars: Spirit, Opportunity, and the Exploration of the Red Planet Hyperion; Reprint edition: 2007
• Hubble Deep Field Video Image: The Most Important Image Man Has Ever Taken
• Extrasolar Planets and Search for Life
• Astronomy Exploration of Planets and Satellites in Comparison With the Earth
• “Mars the Abode of Life” by Percival Lowell
• Mercury Exploration and Space Missions
• The Status of Pluto Needs to Remain as a Planet
• Astronomy: Ancient History of Science
• Cosmology and Astronomical Observation
• Near-Earth Objects and Planetary Defences
• The Search for Life on Titan and Other Planets
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Essays on Mars

There are so many interesting things to learn about Mars, making it a great topic for an essay. Whether you are writing for a school assignment or just want to expand your knowledge, writing an essay about Mars can be both fun and educational.

When choosing a topic for your Mars essay, think about what aspect of the planet interests you the most. You could explore the possibility of life on Mars, the history of Mars exploration, or the potential for future human colonization. There are so many different angles to consider when writing about Mars, so choose a topic that excites you.

If you're considering writing an argumentative essay about Mars, you could explore topics such as the ethical considerations of colonizing Mars, the scientific evidence for past or present life on Mars, or the potential benefits of investing in Mars exploration. For a cause and effect essay, you might consider topics such as the impact of climate change on Mars, the consequences of a successful Mars colonization mission, or the effects of Mars exploration on Earth's economy and technology.

For an opinion essay, you could share your thoughts on whether humans should attempt to colonize Mars, the potential risks and rewards of Mars exploration, or the ethical implications of terraforming Mars. And if you're interested in writing an informative essay, you could explore topics such as the geological features of Mars, the history of Mars exploration missions, or the challenges of living and working on Mars.

• " The potential for human colonization on Mars presents both exciting opportunities and ethical dilemmas. "
• " The search for evidence of past or present life on Mars has significant implications for our understanding of the universe. "
• " Mars exploration missions have provided valuable insights into the planet's climate, geology, and potential for sustaining life. "
• " As humans continue to push the boundaries of space exploration, the idea of colonizing Mars has captured the imagination of scientists, engineers, and aspiring astronauts around the world. "
• " The red planet, Mars, has long been a source of fascination and mystery for scientists and space enthusiasts alike. "
• " The exploration and potential colonization of Mars present both incredible opportunities and complex challenges for humanity. "
• " As we continue to learn more about the red planet, Mars, it is clear that our understanding of the universe and our place within it is forever changed. "

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ORIGINAL RESEARCH article

Simulated gravity field estimation for deimos based on spacecraft tracking data.

• 1 State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, Wuhan University, Wuhan, China
• 2 Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi, China
• 3 Yunnan Observatories, Chinese Academy of Sciences, Kunming, China
• 4 National Key Laboratory of Science and Technology on Aerospace Flight Dynamics, Beijing, China
• 5 Beijing Aerospace Control Center, Beijing, China
• 6 Geodesy Observatory of Tahiti, University of French Polynesia, Tahiti, France

An accurate gravity field model of Deimos can provide constraints for its internal structure modeling, and offer evidence for explaining scientific issues such as the origin of Mars and its moons, and the evolution of the Solar System. The Japanese Martian Moon Exploration (MMX) mission will be launched in the coming years, with a plan to reach Martian orbit after 1 year. However, there is a lack of executed missions targeting Deimos and research on high-precision gravity field of Deimos at this stage. In this study, a 20th-degree gravity field model of Deimos was constructed by scaling the gravity field coefficients of Phobos and combining them with an existing low-degree gravity field model of Deimos. Using simulated ground tracking data generated by three stations of the Chinese Deep Space Network, we simulate precise tracking of a spacecraft in both flyby and orbiting scenarios around Deimos, and the gravity field coefficients of Deimos have been concurrently computed. Comparative experiments have been conducted to explore factors affecting the solution, indicating that the spacecraft’s orbital altitude, the noise level of observation data, and the ephemeris error of Deimos have a significant impact on the solution results. The results of this study can provide references for planning and implementation of missions targeting Martian moons.

1 Introduction

Among the two natural satellites of Mars, Deimos is the smaller one and is further from Mars than Phobos. Traces of the formation and evolution processes on the surface of Mars are not obvious, while the surfaces of the Martian satellites are relatively primitive. Studying the mass, shape, gravity field model, rotation parameters, and internal structure of Deimos can provide a foundation for deducing the formation and evolution of both Deimos and Mars. Furthermore, this may serve as an effective approach to addressing scientific questions such as the formation and evolution of the Earth and the Solar System ( Gao et al., 2021b ). Additionally, Deimos, with its favorable position and weak gravitational field, allows spacecraft to orbit at relatively low altitudes ( Sagdeev and Zakharov, 1989 ). In the future, it could serve as a bridge and supply station for human exploration into deep space ( Guo et al., 2020 ).

Since Asaph Hall’s discovery of Deimos in 1877, humanity has engaged in exploration activities using various methods such as ground observations, the Hubble Telescope, and deep space spacecrafts ( Tieying et al., 2021 ). Especially after the 1970s, various Mars and deep space spacecrafts have been launched, conducting more in-depth investigations of Deimos ( Yang et al., 2019 ). However, there are currently no confirmed exploration missions solely focused on Deimos. Most studies and observations of Deimos have relied on data obtained by spacecrafts during Mars missions. NASA’s Mariner nine spacecraft captured images of Deimos, with the closest distance being 1,200 km and achieving a resolution of 30 m ( Cutts, 1974 ). The Viking 2 orbiter conducted five flyby observations of Deimos, with the closest observation distance being 33 km ( Williams and Friedlander, 2015 ). The European Space Agency’s Mars Express mission (MEX) utilized a high-resolution stereo camera and an imaging spectrometer to reevaluate the volume and density of Deimos and study its surface composition based on observation data ( Witasse et al., 2014 ). NASA’s Mars Reconnaissance Orbiter (MRO) captured the first color high-resolution images of Deimos using the High-Resolution Imaging Science Experiment (HiRISE) camera ( Dunbar, 2009 ). Table 1 summarizes the current knowledge of the orbital parameters and physical properties of Deimos ( Tieying et al., 2021 ) used for our simulation.

Table 1 . The orbital and physical parameters of Deimos.

As one of the two natural satellites of the Earth-like planets in the Solar System, Deimos is attracting more and more attention in the field of deep space exploration. NASA has organized three international conferences on the exploration of Phobos and Deimos ( Lee, 2016 ). Chinese Tianwen-1 spacecraft will conduct further exploration, with potential targets being Phobos and Deimos ( Liu et al., 2023 ). The MMX mission by the Japan Aerospace Exploration Agency (JAXA) was originally scheduled to launch in 2024 and arrive in Martian orbit in 2025 ( Kuramoto et al., 2018 ). It is expected to conduct close-range exploration to the Martian moons, with one of the mission objectives being to calculate the high-degree gravity field of Deimos ( Nakamura et al., 2021 ).

The ephemeris and gravity field of planetary satellites serve as crucial references for the orbit design and planning of planetary satellite exploration missions. The high-precision ephemeris and gravity field of Deimos can ensure the precise entry of the spacecraft into the gravitational influence area of Deimos, thus enabling the implementation of challenging maneuvers such as flyby and orbit insertion ( Guo et al., 2020 ). Currently, there are mainly two methods for calculating the gravity field models of celestial bodies in deep space exploration. The first method is to forward generate the gravity field model of the celestial body based on its precise shape model and a certain density assumption. The second method utilizes close-range orbit tracking data from the spacecraft to extract perturbation information and inversely derive the gravity field model of the celestial body. Method one was employed in Yamamoto et al. (2023) and Guo et al. (2020) for modeling the gravity field of Phobos, while method two was used in Yang et al. (2019) for modeling the gravity field of Phobos. Rubincam et al. (1995) used method one to compute the 4th-degree gravity field of Deimos. However, due to the lack of completed exploration missions specifically targeting Deimos, existing studies and literature on Martian moons predominantly focus on Phobos. Deimos is only briefly mentioned in most Mars satellite research and literature, as seen in the papers of Yamamoto et al. (2023) , Witasse et al. (2014) , and Nakamura et al. (2021) . Moreover, there is scarce research employing method two for modeling the gravity field of Deimos.

In response to the needs of future exploration missions and the shortcomings in current research, this study primarily conducted the following research tasks using ground station simulated radio tracking data. By scaling the gravity field coefficients of Phobos and combining them with existing low-degree gravity field model of Deimos, we constructed a 20th-degree gravity field model of Deimos, which was then tested and corrected based on Kaula criterion ( Kaula and Street, 1967 ). We simulated precise orbit determination for the spacecraft in the flyby and orbiting scenarios. The gravity field coefficients of Deimos were inferred and evaluated for accuracy using simulated orbital data of the spacecraft. Furthermore, comparative experiments were conducted to investigate and analyze the factors affecting the gravity field determination.

2 Model and method

This paper presents our simulation based on scenarios involving the spacecraft’s flyby and orbiting around Deimos, aiming to better adapt to potential changes in the subsequent exploration plan. Based on Wuhan University’s SPOT software system ( Gao et al., 2023 ), we developed precision orbit determination and gravity field parameter estimation software for Deimos.

Since the gravity field of Deimos is weak, the other force models acting on the spacecraft need to be accurately modeled. The inertial motion equation for the spacecraft is shown in Eq. 1 :

The model parameters for the simulation calculations are shown in Table 2 .

Table 2 . Simulation configuration.

As shown in Table 2 , in the flyby and orbiting scenarios, the forces acting on the spacecraft mainly come from Mars and Deimos. For the calculations, the recent 120th degree and order Gravity Model of Mars (GMM-3) ( Genova et al., 2016 ) was chosen as the model for the gravitational field of Mars. In the experimental scenarios, the GM values and positions of major celestial bodies in the Solar System were obtained from the planetary ephemeris DE440 provided by the Jet Propulsion Laboratory (JPL). The state of Mars’ satellites relative to Mars and the GM value for Deimos were obtained from the JPL’s MAR097 ephemeris, with an initial GM value for Deimos set at 9.61556965e-5 km 3 ·s -2 . The positions and GM values for large mass asteroids were provided by the sb441-n16 ephemeris from JPL’s Small-Body Database. The Chinese Deep Space Network consists of the Kashgar, Jiamusi and China-Argentina Deep Space Station, with station coordinates provided by design documents. Additionally, the average radius of Mars is considered to be 3,396 km ( Genova et al., 2016 ). The 4th-degree gravity field of Deimos, calculated by Rubincam et al. (1995) , serves as starting point for the simulation, and detailed numerical values are presented in Table A1 .

This paper primarily evaluates the effectiveness and precision of gravity field recovery through spectral analysis of the gravity field. The expression for the gravitational potential function based on the spherical harmonic expansion is provided ( Heiskanen and Moritz, 1976 ) in Eq. 2 :

where G is the gravitational constant, M is the mass of the central body, R is the reference radius of the central body, r , λ , φ are the spherical coordinates representing the radial distance, longitude, and latitude. C ¯ n m and S ¯ n m are the normalized spherical harmonic coefficients, where n and m represent the degree and order. P ¯ n m sin ⁡ φ is the normalized associated Legendre function.

For a further analysis of the gravity field determination, the accuracy of the calculated gravity field can be assessed through the power spectra, which include the rms coefficient sigma degree variances, σ n and the rms coefficient error degree variances, δ n and Δ n . We choose the same criterion for our study. The equations for calculating these values are shown in Eqs 3 – 5 :

Where σ C ¯ n m and σ S ¯ n m are error variances of the gravity field coefficients C ¯ n m and S ¯ n m , respectively. σ n reflect the magnitude of each degree’s coefficients, δ n and Δ n serve as precision assessment indicators. Typically, the formal errors δ n are retrieved from the posterior covariance matrix of the model, and will stabilize with an increasing number of observations. The true errors Δ n , which reflects the deviation of the calculated results from the reference/true results, are more effective in evaluating the accuracy and reliability of the calculation results.

The Kaula criterion is a statistical model used to describe the expected behavior of the coefficients in a spherical harmonic expansion of the gravity field. In simple terms, the normalized spherical harmonic coefficients exhibit a zero mean property. It states that the degree variance of these coefficients decreases inversely with the α-th power of the degree n . This means that higher-degree coefficients, which correspond to smaller spatial scales, are generally smaller in magnitude. The equation representing this relationship is shown in Eq. 6 :

where k is the constant coefficient of the Kaula criterion curve. The introduction of the Kaula criterion in the determination of the Deimos gravity field model serves as a regularization factor to overcome the instability of solving the gravity field while providing a smoothing effect on the calculation of high-order coefficients.

Constrained by the accumulation of historical data on Deimos, the progress of Martian moon exploration missions like MMX, and the depth of related research, there is currently lack of a priori information on the high-degree and high-precision gravity field of Deimos. Considering the small mass and volume of Deimos, we constructed a 20th-degree gravity field for Deimos as the initial model for the solution. Desprats et al. (2021) constructed the 100th-degree gravity field of Callisto, the fourth moon of Jupiter, whose 3rd to 100th degree coefficients were based on the scaled Moon’s gravity field. In this study, following his approach, we obtained Deimos’ gravity field coefficients from 5th to 20th degree by scaling the coefficients of Phobos provided in Guo et al. (2020) . These scaled coefficients, combined with the 4th-degree coefficients provided by Rubincam et al. (1995) , formed the 20th-degree gravity field of Deimos, which would be involved in the subsequent gravity field solution for Deimos. The scaling factors were calculated based on the GM values and average radii of Phobos and Deimos, and were validated and adjusted according to Kaula criterion. Figure 1 shows the power spectra of the Deimos 20th-degree gravity field generated by scaling.

Figure 1 . Power spectra for the 20th-degree gravity field of Deimos.

As shown in Figure 1 , σ n represents the degree variances of the 20th-degree the Deimos gravity field coefficients. “Kaula4” and “Kaula20” respectively represent the Kaula curves fitted with 4th and 20th degree Deimos gravity field coefficients. The closeness of the two curves in Figure 1 indicates that the scaled initial values of the Deimos 20th-degree gravity field coefficients are reliable and could serve as a reference for subsequent simulation experiments.

After establishing a comprehensive perturbation model for the spacecraft orbit, based on the observation plan set in this study, simulations were conducted to obtain Doppler data through radio tracking observations with an elevation angle of 10° or higher. Simulated observed data, including appropriate noise, were then generated and used to construct a simulated observational dataset. The fitting and iterative refinement process aimed to minimize the sum of squared residuals ( Montenbruck and Gill, 2012 ). Weighted least squares estimation was employed during the solution process, and the calculation equation is shown in Eq. 7 :

where x 0 represents the estimated values of the corrections for the batch processing, H is the Jacobian matrix of the parameters to be estimated, W is the weight matrix of the observed values, y is the residual.

The optimal estimate at the initial moment X ^ 0 , which is also the corrected initial orbit state, can be calculated by the following equation in Eq. 8 :

where X 0 is the initial orbit state.

The simulated observations used in this study are two-way Doppler measurements with a sample rate of 60 s, and the default measurement noise for the observational data was set to Gaussian white noise with a standard deviation of 0.1 mm/s, which represents the precision level of current conventional X-band tracking ( Sun et al., 2023 ). The transformation from the body-fixed coordinate system of Deimos to the inertial coordinate system followed the method recommended by IAU 2015 ( Archinal et al., 2018 ), determined by the right ascension angle α , declination angle δ , and initial prime meridian angle W . For simplicity, errors in angle α , δ , and W were assumed to be ±0.01° based on testing ( Yang, 2023 ). Additionally, this study assumed an error in the time of the periapsis passage of one of Deimos’ orbital elements, as it can only be determined imprecisely through astronomical observations. Assuming an error of 0.01 s in the periapsis time at the initial epoch, this error is equivalent to magnitudes of 10 m for the initial position and 0.001 m/s for the initial velocity in Cartesian coordinates. In our computations, we added the above-mentioned errors to the initial orbit state. Following the approach in Liu et al. (2023) and assuming uniform density for the Deimos, each coefficient of the Deimos gravity field was initially perturbed by adding 0.001 times its own value, serving as the initial model for iterative computation. The uncertainties of estimated parameters were set to three times the formal errors of the solved-for parameters, and the weight matrix was determined by the formal errors.

Table 3 lists different cases considered in the orbiting Scenario to explore the impact of various factors on the determination of the spacecraft’s orbit and the solution of Deimos’ gravity field. In the comparative experiments, only the parameters in Table 3 were changed, while the remaining parameters were kept constant. To simplify calculations, the orbital altitude of the spacecraft in this paper is directly obtained by subtracting the average radius of Deimos (6.24 km) from the distance between the spacecraft and the center of Deimos.

Table 3 . Study cases considered in the simulation.

3.1 Spacecraft orbit perturbation analysis

This section provides a rough estimate of the magnitudes of various perturbations, aiming to facilitate the planning of subsequent simulation exploration and observation scenarios. Figure 2 illustrates the magnitudes of accelerations provided by various perturbative forces on a spacecraft with orbital altitudes ranging from 4 to 100 km at the orbit insertion moment.

Figure 2 . Acceleration magnitude with orbital altitudes ranging from 4 to 100 km.

As shown in Figure 2 , during the close-range exploration of Deimos, the perturbation accelerations provided by Deimos and Mars are predominant. As the spacecraft’s orbital altitude increases from 4 to 100 km, the perturbation acceleration provided by Deimos decreases, while that provided by Mars gradually increases. Starting from an orbital altitude of about 24 km, the perturbation acceleration provided by Mars surpasses that of Deimos. Moreover, the perturbation accelerations provided by solar radiation pressure (“SRP”) and relativistic effects (“Rel”) remain almost unchanged, while those provided by natural celestial bodies (“NB”) slightly increase (mainly from Phobos).

Then, we explored the orbital characteristics of the spacecraft in such a perturbation environment. Figure 3 illustrates the magnitudes of accelerations experienced by the spacecraft in the initial orbits with altitudes of 4 km, 8 km, 12 km, and 30 km during a forward integration of 24 h in the orbiting scenario.

Figure 3 . Acceleration magnitude of the spacecraft’s 24-h orbit in different initial orbital altitudes.

As shown in Figure 3 , the accelerations caused by solar radiation pressure and general relativistic effects for orbits at different altitudes are relatively stable. However, the perturbation acceleration caused by natural celestial bodies undergoes some variations over time. When the initial orbit height is 4 km, the spacecraft can stably orbit Deimos during this period. As the orbit altitude increases, the spacecraft gradually fails to stably orbit Deimos, and it may escape from the orbit after some time of natural motion, transitioning to a state of accompanying or flyby around Deimos. Besides, orbits may also exhibit an accompanying state when the spacecraft makes a very close flyby.

After comprehensive analysis, we adopted a simulation approach based on multi-arc joint adjustment. Different arc lengths were used in the flyby and orbital scenarios to simulate and predict spacecraft’s close-distance exploration of Deimos with maximum fidelity and anticipate data quality. Additionally, in the simulation experiments, prior constraints need to be imposed on several parameters. Table 4 provides the prior constraint configurations for the estimated parameters used in this study.

Table 4 . Priori constraint settings for parameters.

As shown in Table 4 , we assume that these prior constraints can be achieved before the exploration mission phase. After experimental validation, it was found that the numerical values of these prior constraints were relatively loose, with minimal impact on the theoretically calculable results and experimental conclusions. The purpose of setting prior constraints is to ensure the success rate of experimental calculations, improve computational efficiency, especially in comparative experiments.

3.2 Results in the flyby scenario

In the flyby scenario, considering Deimos’ average radius of 6.24 km and the minimum flyby distance of 33 km achieved in historical exploration missions like Viking 2, many simulations were conducted to select instances where the distance from the spacecraft to the center of Deimos falls between 32 km and 48 km. These selected moments served as the initial times for each flyby segment, with the orbital state of Deimos at these initial times being used as the initial orbit state for each segment, resulting in six simulated flyby segments.

The subsatellite point refers to the projection of a spacecraft on the surface of Deimos at a given moment. These points are directly situated along the line connecting the spacecraft and the center of Deimos. The location of the subsatellite points to some extent reflects the coverage of the spacecraft’s orbit over Deimos, which affects the precision of the solution results and the order of the gravitational field that can be solved. In Figure 4 , we have depicted the distribution of the subsatellite points of the spacecraft’s orbit in the flyby scenario. We set the longitude range of the Deimos-fixed frame to be from −180° to 180°, and the latitude range to be from −90° to 90°.

Figure 4 . Distribution of spacecraft’ subsatellite points in the flyby scenario.

As shown in Figure 4 , subsatellite points with an orbit altitude less than 100 km are plotted in the flyby scenario, and only their corresponding orbital data are involved in subsequent calculations. It is observed that in the flyby scenario, the subsatellite points cover a longitude range of approximately ±180°, while ±45° in latitude.

Parameters such as the initial orbit state of each segment, solar radiation pressure coefficient (Cr), etc., were considered as local parameters, while Deimos’ GM and gravity field coefficients were treated as global parameters for computation. A combined approach similar to the method described in Liu. (2022) was used for solving the normal equations, leading to the determination of Deimos gravity field through a joint adjustment. Table 5 presents partial results in the flyby scenario.

Table 5 . Partial results in the flyby scenario.

As shown in Table 5 , the precision of the orbit determination results, denoted by “Formal error”, and their deviation “True error” from reference values demonstrate that the calculation outcomes are favorable. This underpins the premise of the reliability in the gravitational field coefficient computation by this method. The calculation results of Deimos’ GM value and some gravitational field coefficients in this paper are consistent with those in the paper of Rubincam et al. (1995) , and there was an improvement in the calculation precision. Figure 5 illustrates the power spectra of the gravity field solution for Deimos in the flyby scenario.

Figure 5 . Power spectra of the gravity field solution in the flyby scenario.

The “Ref coefficients” in Figure 5 is equivalent to “ σ n ” in Figure 1 , which represents the variance of the gravity field coefficients of Deimos. The trend of the power spectrum lines and their intersections indicate that only up to the 3rd-degree coefficients of the gravitational field of Deimos can be solvable and reliably estimated in the flyby scenario. In this paper, we set the maximum degree on the x -axis of the power spectra figure to the solvable degree plus 1 or 2 to highlight the solution results.

The results in Figure 5 show that, even under relatively ideal experimental conditions and with efforts to maximize the span of closer flyby data, the two-way Doppler data between ground stations and the spacecraft provided constraints only on the lower-degree coefficients of Deimos’ gravity field. The higher-degree coefficients are largely unconstrained. We speculate that this is primarily related to both spacecraft altitude and to a very sparse spatial coverage of the surface, which does not allow for highly-resolved probing of the gravity field in the flyby scenario.

3.3 Results in the orbiting scenario

If more accurate gravity field data of Deimos is required through spacecraft orbit inversion, it is necessary to consider scenarios where the spacecraft orbits around Deimos. When conducting simulation experiments in the orbiting scenario, it is considered that the spacecraft may not be able to orbit Deimos continuously and stably for a long time as the orbital altitude increases. Therefore, the adopted scheme for obtaining simulation segments was as follows. From the simulation period, 30 simulation moments spaced 12 h apart were selected. And at these moments, initial orbit state at specified orbital altitudes were generated by our design functions. We performed orbit integration separately for each set of initial orbit state for 12 h, resulting in 30 orbiting segments. Figure 6 depicts the distribution of subsatellite points in the orbiting scenario.

Figure 6 . Distribution of spacecraft’ subsatellite points in the flyby scenario.

As shown in Figure 6 , in the orbiting scenario, the subsatellite points cover a latitude range of approximately −80°–70°, while achieving full coverage in longitude. Compared to in the flyby scenario, the distribution of orbiting subsatellite points is more uniform. This indicates that the orbital data in the orbiting scenario is more effective and reliable.

Similar to in the flyby scenario, the parameters of each segment in the orbiting scenario were divided into local and global parameters for computation. The least squares method was employed to solve the gravity field of Deimos by combining the normal equations of multiple segments. Table 6 presents partial results of the gravity field of Deimos obtained in the orbiting scenario, with the spacecraft’s initial orbit altitude approximately 4 km.

Table 6 . Partial results in the orbiting scenario.

As shown in Table 6 , Deimos’ calculated GM is 9.61541e-5 ± 5.94597e-9 km 3 ·s-2, C20 is −0.107897 ± 3.97807e-6, C22 is 3.08143e-2 ± 4.60863e-6, et al. Using accuracy metrics as the evaluation criterion, the computational results in the orbiting scenario are superior to those in the flyby scenario. Figure 7 shows the corresponding results’ power spectra.

Figure 7 . Power spectra of the gravity field solution in the orbiting scenario.

As shown in Figure 7 , the orbit state with an initial orbit altitude of 4 km can calculate up to the 10th degree. Figures 5 , 7 indicate that the accuracy of the Deimos gravity field coefficient calculation in the orbiting scenario is generally better and more stable compared to in the flyby scenario. The improvement in accuracy is particularly noticeable in the calculation of lower-degree coefficients, and can make it easier to confirm the effective degrees of the gravity model.

Additionally, Table 7 summarizes the Deimos GM calculation results from this study and selected literature. As shown in Table 7 , the Deimos GM calculation results from this study are consistent with previously published findings, with significantly improved accuracy.

Table 7 . Solutions for the gravitational constants (GM) of Deimos.

3.4 Analysis of influential factors

We adjusted the parameters outlined in Table 3 for comparative experiments and the influence of various factors on the experimental outcomes was explored. Considering that in the orbiting scenario, the precision of the calculated results significantly surpassed which in the flyby scenario, and the former demonstrated greater sensitivity to changes in influencing factors than the latter, only comparative experimental outcomes in the orbiting scenario were presented. As the formal error δ n is simultaneously influenced by a substantial accumulation of observations, the coefficient error variance Δ n was prioritized as the evaluation criterion.

Initially, the impact of the initial orbit altitude on the calculation outcomes was investigated. Typically, in the orbiting scenario, the spacecraft’s initial orbit altitude largely determined the range of integrated orbit altitudes. Meanwhile the integrated orbit altitudes may fall below the initial orbit altitude. Based on safety considerations and experimental validation, this study ultimately selected 4 km as the minimum simulated orbit altitude. Figure 6 illustrates the power spectra under different initial orbit altitudes.

As shown in Figure 8 , it is worth noting that with the increase in the initial orbit altitude within a certain range, the perturbation force provided by Deimos decreased, while the perturbation effect from Mars gradually became more significant, leading to a gradual reduction in the accuracy of gravity field and the solvable degree of calculation. In our experiments, as the spacecraft’s initial orbit increased from 4 km to 8 km, the maximum degree of Deimos’ gravity field that could be calculated decreased by approximately 2–3°. Furthermore, due to the extremely weak gravity field of Deimos, the spacecraft may gradually fail to sustain long-term orbiting in its natural state, and may even escape Deimos’ orbit, transitioning to a state of flyby or accompanying. In fact, it can also be roughly inferred that the enhancement in calculation accuracy from the flyby scenario to the orbiting scenario primarily stemmed from the reduction in orbit altitude. Taking these factors into consideration, attention should be paid to the orbital altitude threshold when designing orbiting trajectories, with altitudes of 4–8 km above Deimos’ surface being deemed more appropriate.

Figure 8 . Power spectra in case 1 listed in Table 3 (Different initial orbital altitudes).

The observation noise determines the quality of the observation data, thereby affecting the precision of gravity field calculation results. Therefore, it was necessary to investigate the influence of observation data noise level on the calculation. In this comparative experiment, we set the observation noise level to three levels: 1e-6, 1e-7, and 1e-8 km/s Figure 7 depicted the power spectra of the calculation results obtained using observation data with different noise levels.

As shown in Figure 9 , when the observation noise level decreased from 1e-6 km/s to 1e-8 km/s, the calculation precision improved by approximately five orders of magnitude. Gaussian white noise of 1e-7 km/s represented the current conventional X-band tracking precision level and was also the default level added in all other experiments. Filtering can reduce the noise level of observation data with large noise, but the ability to reduce noise level is limited by the current level of miniaturization and physical characteristics of onboard electronic devices. Therefore, the settings of 1e-6 and 1e-8 km/s noise levels were only indicative.

Figure 9 . Power spectra in case 2 listed in Table 3 (Different noise levels).

In the simulations described above, the state of Deimos relative to Mars was directly obtained from JPL’s MAR097 ephemeris, assuming that there were no errors in the Deimos ephemeris. However, estimating the effect of ephemeris errors on parameter estimation is a crucial consideration. In the simulation experiments, following the approach of Gao et al. (2021a) and Sun et al. (2023) , experiments were conducted by introducing different levels of errors along the trajectory direction of Deimos to investigate the impact of ephemeris errors. In this study, errors were introduced into the Deimos ephemerides at magnitudes of 0, 0.5, 1, and 2 km, respectively. Figure 8 illustrates the power spectra of the calculation results using Deimos ephemerides with different error magnitudes.

As shown in Figure 10 , in cases where the ephemeris error is less than 0.5 km, the differences in the power spectra of gravity field coefficients are relatively small. However, in cases with ephemeris error of 1 km, deviations in the high-degree gravity field can be observed. While ephemeris error rises to 2 km, even the calculation of the low-degree coefficients shows obvious deviation. The results indicate that Deimos ephemeris errors of more than 0.5 km could affect the solution of higher degree coefficients, while ephemeris errors of more than 1 km will significantly deteriorate the precision of gravity field estimation. Therefore, it is important to ensure that the ephemeris error of Deimos is less than 0.5 km in practical measurements. We need to ensure that the ephemeris error is less than 1 km, which is realistic and feasible indicated in the work of Gao et al. (2021a) .

Figure 10 . Power spectra in Case 3 listed in Table 3 (Different Deimos ephemeris errors).

The sunlight radiation impinging on the surface of the spacecraft exerts pressure, thereby influencing its orbit. In this study, a simplified approach was employed, treating the spacecraft as spherical and assuming that the sunlight rays are always perpendicular to the spacecraft surface for modeling solar radiation pressure. The simplified equation for calculating solar radiation pressure is shown in Eq. 9 :

where C r is the SRP coefficient, primarily determined by the spacecraft’s surface material, typically treated as an estimated parameter in precise orbit determination, r represents the position vector of the Sun relative to the spacecraft, P s denotes the solar radiation pressure per unit area at a distance r , typically taken as 4.56 × 10 −6 N m −2 , A and m are the surface area and mass of the spacecraft.

It is necessary to note that the spacecraft is not always fully exposed to solar radiation, and shadowing due to celestial bodies needs to be considered. In such cases, Formula 7 should be multiplied by a shadowing coefficient v .

In this study, the numerical value of Cr was set to 1.2. In comparative experiments, errors of 0%, 10%, 20%, and 30% were respectively added to the Cr values to investigate the impact of Cr errors on the calculation results. Figure 11 illustrates the power spectra of the calculation results with the aforementioned errors added to Cr.

Figure 11 . Power spectra in Case 4 listed in Table 3 (Different Cr errors).

As shown in Figure 11 , the addition of Cr errors has a relatively small impact on the variance of the true error of the gravitational field coefficients, and it hardly affects the formal error. In the orbiting scenario, the perturbation force provided by solar radiation pressure is much smaller and relatively stable compared to that provided by Mars and Deimos.

4 Discussion and conclusion

This paper addresses gravity field recovery at Deimos under multiple exploration scenarios, with a focus on Martian moon exploration missions. Based on simulated ground tracking data, the paper conducts precise orbit determination of spacecraft with close orbit around Deimos and inversely estimates the gravity field model of Deimos. The main work and innovations of this paper are summarized as follows.

Based on the available low-order gravity field coefficients of Deimos and rescaled gravity field coefficients of Phobos, we constructed of a 20th-degree gravity field model of Deimos, and the Kaula criterion was applied for validation and adjustment. Simulated analyses were conducted separately in the flyby and orbiting scenarios around Deimos, establishing force models and observation models for spacecraft. Then we analyzed and evaluated the calculated results to determine the effective degrees for inversion of the Deimos gravity field. Factors affecting the accuracy of the calculation and their respective influences were studied and analyzed through comparative experiments. From the experiment results of this study, it is evident that, based on the current technological capabilities, the altitude of the spacecraft relative to Deimos has the greatest impact on the accuracy of the calculations. Under the influence of Martian perturbations, increasing the spacecraft’s altitude leads to a sharp decrease in the accuracy of the calculations and the feasible degree of gravity field coefficients. Then, the level of noise in the observation data and the errors in Deimos’ ephemeris play significant roles, but the former can be addressed through improvements in observation methods and equipment, while the latter can be constrained by precise orbit determination of Deimos. Conversely, errors in the solar radiation pressure coefficient have a relatively minor impact on the calculation results. Furthermore, this paper compared the calculated GM with existing findings, indicating that a targeted mission would significantly reduce error bars of GM. Additionally, various parameter evaluation criteria were employed to demonstrate the reliability of the results obtained in this study.

This study utilized simulated data, and the orbit state around Deimos were conducted at relatively close distances. Moreover, in the processing of actual radio tracking data, besides minor effects from modeling factors like solar radiation pressure, there are significant long-term impacts from errors in rotation models and celestial ephemerides ( Liu et al., 2023 ). Due to the simplifications made during the simulation, the results of the study may be somewhat idealized. However, the experimental process and data processing methods still hold relevant reference value. In future real data processing endeavors, finer adjustments or modeling efforts will be planned to achieve high precision outcomes.

The gravity field of Deimos is of significant importance for scientific research and deep space exploration within the Martian system. The computational results presented in this paper can serve as a priori gravity field models for Martian moon exploration missions, providing theoretical foundations for spacecraft navigation and landing orbit determination. Additionally, they offer valuable insights for the planning and implementation of future exploration missions to Mars and its satellites by various countries.

Data availability statement

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Author contributions

WS: Data curation, Formal Analysis, Software, Writing–original draft. JY: Conceptualization, Funding acquisition, Supervision, Writing–review and editing. SS: Software, Writing–review and editing. YY: Validation, Writing–review and editing. SL: Validation, Writing–review and editing. ZW: Supervision, Visualization, Writing–review and editing. J-PB: Supervision, Writing–review and editing.

The author(s) declare that financial support was received for the research, authorship, and/or publication of this article. This work is supported by the National Key Research and Development Program of China (No. 2022YFF0503202) and the National Natural Science Foundation of China (42241116). JY is supported by the Macau Science and Technology Development Fund [No. SKL-LPS(MUST)-2021-2023] and the 2022 Project of Xinjiang Uygur Autonomous Region of China for Heaven Lake Talent Program; ZW is supported by the Chinese Academy of Sciences Foundation of the young scholars of western (2020-XBQNXZ-019) and the open project of the Key Laboratory in Xinjiang Uygur Autonomous Region of China (2023D04058); and J-PB is supported by a DAR grant in planetology from the French Space Agency (CNES).

Acknowledgments

We sincerely appreciate the reviewers and the editor for their constructive comments, which greatly improved our submission manuscript.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

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As shown in Table A1 , in the Appendix , we give the reference gravity field model of Deimos that is generated from the shape model. The gravity field model of Deimos is given up to degree and order of 4.

TABLE A1 . The reference gravity field model of Deimos.

Keywords: Deimos, gravity field, flyby, orbiting, accuracy

Citation: Su W, Yan J, Sun S, Yang Y, Liu S, Wang Z and Barriot J-P (2024) Simulated gravity field estimation for Deimos based on spacecraft tracking data. Front. Astron. Space Sci. 11:1411703. doi: 10.3389/fspas.2024.1411703

Received: 03 April 2024; Accepted: 24 July 2024; Published: 13 August 2024.

Reviewed by:

Copyright © 2024 Su, Yan, Sun, Yang, Liu, Wang and Barriot. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Jianguo Yan, [email protected]

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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Research Article

Archaeology in space: The Sampling Quadrangle Assemblages Research Experiment (SQuARE) on the International Space Station. Report 1: Squares 03 and 05

Roles Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Visualization, Writing – original draft, Writing – review & editing

* E-mail: [email protected]

Affiliations Department of Art, Chapman University, Orange, CA, United States of America, Space Engineering Research Center, University of Southern California, Marina del Rey, CA, United States of America

Roles Data curation, Formal analysis, Investigation, Methodology, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing

Affiliation Department of History, Carleton University, Ottawa, ON, United States of America

Roles Conceptualization, Data curation, Methodology, Project administration, Supervision, Writing – review & editing

Affiliation College of Humanities, Arts and Social Sciences, Flinders University, Adelaide, Australia

Roles Software, Writing – original draft

Roles Investigation, Writing – original draft

Affiliation Archaeology Research Center, University of Southern California, Los Angeles, CA, United States of America

• Justin St. P. Walsh, 
• Shawn Graham, 
• Alice C. Gorman, 
• Chantal Brousseau, 
• Salma Abdullah

• Published: August 7, 2024
• https://doi.org/10.1371/journal.pone.0304229
• Reader Comments

Between January and March 2022, crew aboard the International Space Station (ISS) performed the first archaeological fieldwork in space, the Sampling Quadrangle Assemblages Research Experiment (SQuARE). The experiment aimed to: (1) develop a new understanding of how humans adapt to life in an environmental context for which we are not evolutionarily adapted, using evidence from the observation of material culture; (2) identify disjunctions between planned and actual usage of facilities on a space station; (3) develop and test techniques that enable archaeological research at a distance; and (4) demonstrate the relevance of social science methods and perspectives for improving life in space. In this article, we describe our methodology, which involves a creative re-imagining of a long-standing sampling practice for the characterization of a site, the shovel test pit. The ISS crew marked out six sample locations (“squares”) around the ISS and documented them through daily photography over a 60-day period. Here we present the results from two of the six squares: an equipment maintenance area, and an area near exercise equipment and the latrine. Using the photographs and an innovative webtool, we identified 5,438 instances of items, labeling them by type and function. We then performed chronological analyses to determine how the documented areas were actually used. Our results show differences between intended and actual use, with storage the most common function of the maintenance area, and personal hygiene activities most common in an undesignated area near locations for exercise and waste.

Citation: Walsh JSP, Graham S, Gorman AC, Brousseau C, Abdullah S (2024) Archaeology in space: The Sampling Quadrangle Assemblages Research Experiment (SQuARE) on the International Space Station. Report 1: Squares 03 and 05. PLoS ONE 19(8): e0304229. https://doi.org/10.1371/journal.pone.0304229

Editor: Peter F. Biehl, University of California Santa Cruz, UNITED STATES OF AMERICA

Received: March 9, 2024; Accepted: May 7, 2024; Published: August 7, 2024

Copyright: © 2024 Walsh et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the paper and its Supporting Information files.

Funding: JW was the recipient of funding from Chapman University’s Office of Research and Sponsored Programs to support the activities of Axiom Space as implementation partner for the research presented in this article. There are no associated grant numbers for this financial support. Axiom Space served in the role of a contractor hired by Chapman University for the purpose of overseeing logistics relating to our research. In-kind support in the form of ISS crew time and access to the space station’s facilities, also awarded to JW from the ISS National Laboratory, resulted from an unsolicited proposal, and therefore there is no opportunity title or number associated with our work. No salary was received by any of the investigators as a result of the grant support. No additional external funding was received for this study.

Competing interests: The authors have declared that no competing interests exist.

Introduction

The International Space Station Archaeological Project (ISSAP) aims to fill a gap in social science investigation into the human experience of long-duration spaceflight [ 1 – 3 ]. As the largest, most intensively inhabited space station to date, with over 270 visitors from 23 countries during more than 23 years of continuous habitation, the International Space Station (ISS) is the ideal example of a new kind of spacefaring community—“a microsociety in a miniworld” [ 4 ]. While it is possible to interview crew members about their experiences, the value of an approach focused on material culture is that it allows identification of longer-term patterns of behaviors and associations that interlocutors are unable or even unwilling to articulate. In this respect, we are inspired by previous examples of contemporary archaeology such as the Tucson Garbage Project and the Undocumented Migration Project [ 5 – 7 ]. We also follow previous discussions of material culture in space contexts that highlight the social and cultural features of space technology [ 8 , 9 ].

Our primary goal is to identify how humans adapt to life in a new environment for which our species has not evolved, one characterized by isolation, confinement, and especially microgravity. Microgravity introduces opportunities, such as the ability to move and work in 360 degrees, and to carry out experiments impossible in full Earth gravity, but also limitations, as unrestrained objects float away. The most routine activities carried out on Earth become the focus of intense planning and technological intervention in microgravity. By extension, our project also seeks to develop archaeological techniques that permit the study of other habitats in remote, extreme, or dangerous environments [ 10 , 11 ]. Since it is too costly and difficult to visit our archaeological site in person, we have to creatively re-imagine traditional archaeological methods to answer key questions. To date, our team has studied crew-created visual displays [ 12 , 13 ], meanings and processes associated with items returned to Earth [ 14 ], distribution of different population groups around the various modules [ 15 ], and the development of machine learning (ML) computational techniques to extract data about people and places, all from historic photographs of life on the ISS [ 16 ].

From January to March 2022, we developed a new dataset through the first archaeological work conducted off-Earth. We documented material culture in six locations around the ISS habitat, using daily photography taken by the crew which we then annotated and studied as evidence for changes in archaeological assemblages of material culture over time. This was the first time such data had been captured in a way that allowed statistical analysis. Here, we present the data and results from Squares 03 and 05, the first two sample locations to be completed.

Materials and methods

Square concept and planning.

Gorman proposed the concept behind the investigation, deriving it from one of the most traditional terrestrial archaeological techniques, the shovel test pit. This method is used to understand the overall characteristics of a site quickly through sampling. A site is mapped with a grid of one-meter squares. Some of the squares are selected for initial excavation to understand the likely spatial and chronological distribution of features across the entire site. In effect, the technique is a way to sample a known percentage of the entire site systematically. In the ISS application of this method, we documented a notional stratigraphy through daily photography, rather than excavation.

Historic photography is a key dataset for the International Space Station Archaeological Project. Tens of thousands of images have been made available to us, either through publication [ 17 ], or through an arrangement with the ISS Research Integration Office, which supplied previously unpublished images from the first eight years of the station’s habitation. These photographs are informative about the relationships between people, places, and objects over time in the ISS. However, they were taken randomly (from an archaeological perspective) and released only according to NASA’s priorities and rules. Most significantly, they were not made with the purpose of answering archaeological questions. By contrast, the photographs taken during the present investigation were systematic, representative of a defined proportion of the habitat’s area, and targeted towards capturing archaeology’s primary evidence: material culture. We were interested in how objects move around individual spaces and the station, what these movements revealed about crew adherence to terrestrial planning, and the creative use of material culture to make the laboratory-like interior of the ISS more habitable.

Access to the field site was gained through approval of a proposal submitted to the Center for the Advancement of Science in Space (also known as the ISS National Laboratory [ISS NL]). Upon acceptance, Axiom Space was assigned as the Implementation Partner for carriage of the experiment according to standard procedure. No other permits were required for this work.

Experiment design

Since our work envisioned one-meter sample squares, and recognizing the use of acronyms as a persistent element of spacefaring culture, we named our payload the Sampling Quadrangle Assemblages Research Experiment (SQuARE). Permission from the ISS NL to conduct SQuARE was contingent on using equipment that was already on board the space station. SQuARE required only five items: a camera, a wide-angle lens, adhesive tape (for marking the boundaries of the sample locations), a ruler (for scale), and a color calibration card (for post-processing of the images). All of these were already present on the ISS.

Walsh performed tests on the walls of a terrestrial art gallery to assess the feasibility of creating perfect one-meter squares in microgravity. He worked on a vertical surface, using the Pythagorean theorem to determine where the corners should be located. The only additional items used for these tests were two metric measuring tapes and a pencil for marking the wall (these were also already on the ISS). While it was possible to make a square this way, it also became clear that at least two people were needed to manage holding the tape measures in position while marking the points for the corners. This was not possible in the ISS context.

Walsh and Gorman identified seven locations for the placement of squares. Five of these were in the US Orbital Segment (USOS, consisting of American, European, and Japanese modules) and two in the Russian Orbital Segment. Unfortunately, tense relations between the US and Russian governments meant we could only document areas in the USOS. The five locations were (with their SQuARE designations):

• 01—an experimental rack on the forward wall, starboard end, of the Japanese Experiment Module
• 02—an experimental rack on the forward wall, port end, of the European laboratory module Columbus
• 03—the starboard Maintenance Work Area (workstation) in the US Node 2 module
• 04—the wall area “above” (according to typical crew body orientation) the galley table in the US Node 1 module
• 05—the aft wall, center location, of the US Node 3 module

Our square selection encompassed different modules and activities, including work and leisure. We also asked the crew to select a sixth sample location based on their understanding of the experiment and what they thought would be interesting to document. They chose a workstation on the port wall of the US laboratory module, at the aft end, which they described in a debriefing following their return to Earth in June 2022 as “our central command post, like our shared office situation in the lab.” Results from the four squares not included here will appear in future publications.

Walsh worked with NASA staff to determine payload procedures, including precise locations for the placement of the tape that would mark the square boundaries. The squares could not obstruct other facilities or experiments, so (unlike in terrestrial excavations, where string is typically used to demarcate trench boundaries) only the corners of each square were marked, not the entire perimeter. We used Kapton tape due to its bright yellow-orange color, which aided visibility for the crew taking photographs and for us when cropping the images. In practice, due to space constraints, the procedures that could actually be performed by crew in the ISS context, and the need to avoid interfering with other ongoing experiments, none of the locations actually measured one square meter or had precise 90° corners like a trench on Earth.

On January 14, 2022, NASA astronaut Kayla Barron set up the sample locations, marking the beginning of archaeological work in space ( S1 Movie ). For 30 days, starting on January 21, a crew member took photos of the sample locations at approximately the same time each day; the process was repeated at a random time each day for a second 30-day period to eliminate biases. Photography ended on March 21, 2022. The crew were instructed not to move any items prior to taking the photographs. Walsh led image management, including color and barrel distortion correction, fixing the alignment of each image, and cropping them to the boundaries of the taped corners.

Data processing—Item tagging, statistics, visualizations

We refer to each day’s photo as a “context” by analogy with chronologically-linked assemblages of artifacts and installations at terrestrial archaeological sites ( S1 and S2 Datasets). As previously noted, each context represented a moment roughly 24 hours distant from the previous one, showing evidence of changes in that time. ISS mission planners attempted to schedule the activity at the same time in the first month, but there were inevitable changes due to contingencies. Remarkably, the average time between contexts in Phase 1 was an almost-perfect 24h 0m 13s. Most of the Phase 1 photos were taken between 1200 and 1300 GMT (the time zone in which life on the ISS is organized). In Phase 2, the times were much more variable, but the average time between contexts during this period was still 23h 31m 45s. The earliest Phase 2 photo was taken at 0815 GMT, and the latest at 2101. We did not identify any meaningful differences between results from the two phases.

Since the “test pits” were formed of images rather than soil matrices, we needed a tool to capture information about the identity, nature, and location of every object. An open-source image annotator platform [ 18 ] mostly suited our needs. Brousseau rebuilt the platform to work within the constraints of our access to the imagery (turning it into a desktop tool with secure access to our private server), to permit a greater range of metadata to be added to each item or be imported, to autosave, and to export the resulting annotations. The tool also had to respect privacy and security limitations required by NASA.

The platform Brousseau developed and iterated was rechristened “Rocket-Anno” ( S1 File ). For each context photograph, the user draws an outline around every object, creating a polygon; each polygon is assigned a unique ID and the user provides the relevant descriptive information, using a controlled vocabulary developed for ISS material culture by Walsh and Gorman. Walsh and Abdullah used Rocket-Anno to tag the items in each context for Squares 03 and 05. Once all the objects were outlined for every context’s photograph, the tool exported a JSON file with all of the metadata for both the images themselves and all of the annotations, including the coordinate points for every polygon ( S3 Dataset ). We then developed Python code using Jupyter “notebooks” (an interactive development environment) that ingests the JSON file and generates dataframes for various facets of the data. Graham created a “core” notebook that exports summary statistics, calculates Brainerd-Robinson coefficients of similarity, and visualizes the changing use of the square over time by indicating use-areas based on artifact types and subtypes ( S2 File ). Walsh and Abdullah also wrote detailed square notes with context-by-context discussions and interpretations of features and patterns.

We asked NASA for access to the ISS Crew Planner, a computer system that shows each astronaut’s tasks in five-minute increments, to aid with our interpretation of contexts, but were denied. As a proxy, we use another, less detailed source: the ISS Daily Summary Reports (DSRs), published on a semi-regular basis by NASA on its website [ 19 ]. Any activities mentioned in the DSRs often must be connected with a context by inference. Therefore, our conclusions are likely less precise than if we had seen the Crew Planner, but they also more clearly represent the result of simply observing and interpreting the material culture record.

The crew during our sample period formed ISS Expedition 66 (October 2021-March 2022). They were responsible for the movement of objects in the sample squares as they carried out their daily tasks. The group consisted of two Russians affiliated with Roscosmos (the Russian space agency, 26%), one German belonging to the European Space Agency (ESA, 14%), and four Americans employed by NASA (57%). There were six men (86%) and one woman (14%), approximately equivalent to the historic proportions in the ISS population (84% and 16%, respectively). The Russian crew had their sleeping quarters at the aft end of the station, in the Zvezda module. The ESA astronaut slept in the European Columbus laboratory module. The four NASA crew slept in the US Node 2 module (see below). These arrangements emphasize the national character of discrete spaces around the ISS, also evident in our previous study of population distributions [ 15 ]. Both of the sample areas in this study were located in US modules.

Square 03 was placed in the starboard Maintenance Work Area (MWA, Fig 1 ), one of a pair of workstations located opposite one another in the center of the Node 2 module, with four crew berths towards the aft and a series of five ports for the docking of visiting crew/cargo vehicles and two modules on the forward end ( Fig 2 ). Node 2 (sometimes called “Harmony”) is a connector that links the US, Japanese, and European lab modules. According to prevailing design standards when the workstation was developed, an MWA “shall serve as the primary location for servicing and repair of maximum sized replacement unit/system components” [ 20 ]. Historic images published by NASA showing its use suggested that its primary function was maintenance of equipment and also scientific work that did not require a specific facility such as a centrifuge or furnace.

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An open crew berth is visible at right. The yellow dotted line indicates the boundaries of the sample area. Credit: NASA/ISSAP.

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Credit: Tor Finseth, by permission, modified by Justin Walsh.

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Square 03 measured 90.3 cm (top) x 87.8 (left) x 89.4 (bottom) x 87.6 (right), for an area of approximately 0.79 m 2 . Its primary feature was a blue metal panel with 40 square loop-type Velcro patches arranged in four rows of ten. During daily photography, many items were attached to the Velcro patches (or held by a clip or in a resealable bag which had its own hook-type Velcro). Above and below the blue panel were additional Velcro patches placed directly on the white plastic wall surface. These patches were white, in different sizes and shapes and irregularly arranged, indicating that they had been placed on the wall in response to different needs. Some were dirty, indicating long use. The patches below the blue panel were rarely used during the sample period, but the patches above were used frequently to hold packages of wet wipes, as well as resealable bags with electrostatic dispersion kits and other items. Outside the sample area, the primary features were a crew berth to the right, and a blue metal table attached to the wall below. This table, the primary component of the MWA, “provides a rigid surface on which to perform maintenance tasks,” according to NASA [ 21 ]. It is modular and can be oriented in several configurations, from flat against the wall to horizontal ( i . e ., perpendicular to the wall). A laptop to the left of the square occasionally showed information about work happening in the area.

In the 60 context photos of Square 03, we recorded 3,608 instances of items, an average of 60.1 (median = 60.5) per context. The lowest count was 24 in context 2 (where most of the wall was hidden from view behind an opaque storage bag), and the highest was 75 in both contexts 20 and 21. For comparison between squares, we can also calculate the item densities per m 2 . The average count was 76.1/m 2 (minimum = 30, maximum = 95). The count per context ( Fig 3(A)) began much lower than average in the first three contexts because of a portable glovebag and a stowage bag that obscured much of the sample square. It rose to an above-average level which was sustained (with the exception of contexts 11 and 12, which involved the appearance of another portable glovebag) until about context 43, when the count dipped again and the area seemed to show less use. Contexts 42–59 showed below-average numbers, as much as 20% lower than previously.

(a) Count of artifacts in Square 03 over time. (b) Proportions of artifacts by function in Square 03. Credit: Rao Hamza Ali.

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74 types of items appeared at least once here, belonging to six categories: equipment (41%), office supplies (31%), electronic (17%), stowage (9%), media (1%), and food (<1%). To better understand the significance of various items in the archaeological record, we assigned them to functional categories ( Table 1 , Fig 3(B)) . 35% of artifacts were restraints, or items used for holding other things in place; 12% for tools; 9% for containers; 9% for writing items; 6% for audiovisual items; 6% for experimental items; 4% for lights; 4% for safety items; 4% for body maintenance; 4% for power items; 3% for computing items; 1% for labels; and less than 1% drinks. We could not identify a function for two percent of the items.

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One of the project goals is understanding cultural adaptations to the microgravity environment. We placed special attention on “gravity surrogates,” pieces of (often simple) technology that are used in space to replicate the terrestrial experience of things staying where they are placed. Gravity surrogates include restraints and containers. It is quite noticeable that gravity surrogates comprise close to half of all items (44%) in Square 03, while the tools category, which might have been expected to be most prominent in an area designated for maintenance, is less than one-third as large (12%). Adding other groups associated with work, such as “experiment” and “light,” only brings the total to 22%.

Square 05 (Figs 2 and 4 ) was placed in a central location on the aft wall of the multipurpose Node 3 (“Tranquility”) module. This module does not include any specific science facilities. Instead, there are two large pieces of exercise equipment, the TVIS (Treadmill with Vibration Isolation Stabilization System, on the forward wall at the starboard end), and the ARED (Advanced Resistive Exercise Device, on the overhead wall at the port end). Use of the machines forms a significant part of crew activities, as they are required to exercise for two hours each day to counteract loss of muscle mass and bone density, and enable readjustment to terrestrial gravity on their return. The Waste and Hygiene Compartment (WHC), which includes the USOS latrine, is also here, on the forward wall in the center of the module, opposite Square 05. Finally, three modules are docked at Node 3’s port end. Most notable is the Cupola, a kind of miniature module on the nadir side with a panoramic window looking at Earth. This is the most popular leisure space for the crew, who often describe the hours they spend there. The Permanent Multipurpose Module (PMM) is docked on the forward side, storing equipment, food, and trash. In previous expeditions, some crew described installing a curtain in the PMM to create a private space for changing clothes and performing body maintenance activities such as cleaning oneself [ 22 , 23 ], but it was unclear whether that continued to be its function during the expedition we observed. One crew member during our sample period posted a video on Instagram showing the PMM interior and their efforts to re-stow equipment in a bag [ 24 ]. The last space attached to Node 3 is an experimental inflatable module docked on the aft side, called the Bigelow Expandable Activity Module (BEAM), which is used for storage of equipment.

The yellow dotted line indicates the boundaries of the sample area. The ARED machine is at the far upper right, on the overhead wall. The TVIS treadmill is outside this image to the left, on the forward wall. The WHC is directly behind the photographer. Credit: NASA/ISSAP.

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Square 05 was on a mostly featureless wall, with a vertical handrail in the middle. Handrails are metal bars located throughout the ISS that are used by the crew to hold themselves in place or provide a point from which to propel oneself to another location. NASA’s most recent design standards acknowledge that “[t]hey also serve as convenient locations for temporary mounting, affixing, or restraint of loose equipment and as attachment points for equipment” [ 25 ]. The handrail in Square 05 was used as an impromptu object restraint when a resealable bag filled with other bags was squeezed between the handrail and the wall.

The Brine Processing Assembly (BPA), a white plastic box which separates water from other components of urine for treatment and re-introduction to the station’s drinkable water supply [ 26 ], was fixed to the wall outside the square boundaries at lower left. A bungee cord was attached to both sides of the box; the one on the right was connected at its other end to the handrail attachment bracket. Numerous items were attached to or wedged into this bungee cord during the survey, bringing “gravity” into being. A red plastic duct ran through the square from top center into the BPA. This duct led from the latrine via the overhead wall. About halfway through the survey period, in context 32, the duct was wrapped in Kapton tape. According to the DSR for that day, “the crew used duct tape [ sic ] to make a seal around the BPA exhaust to prevent odor permeation in the cabin” [ 27 ], revealing an aspect of the crew’s experience of this area that is captured only indirectly in the context photograph. Permanently attached to the wall were approximately 20 loop-type Velcro patches in many shapes and sizes, placed in a seemingly random pattern that likely indicates that they were put there at different times and for different reasons.

Other common items in Square 05 were a mirror, a laptop computer, and an experimental item belonging to the German space agency DLR called the Touch Array Assembly [ 28 ]. The laptop moved just three times, and only by a few centimeters each time, during the sample period. The Touch Array was a black frame enclosing three metal surfaces which were being tested for their bacterial resistance; members of the crew touched the surfaces at various moments during the sample period. Finally, and most prominent due to its size, frequency of appearance, and use (judged by its movement between context photos) was an unidentified crew member’s toiletry kit.

By contrast with Square 03, 05 was the most irregular sample location, roughly twice as wide as it was tall. Its dimensions were 111 cm (top) x 61.9 (left) x 111.4 (bottom) x 64.6 (right), for an area of approximately 0.7 m 2 , about 89% of Square 03. We identified 1,830 instances of items in the 60 contexts, an average of 30.5 (median = 32) per context. The minimum was 18 items in context 5, and the maximum was 39 in contexts 24, 51, and 52. The average item density was 43.6/m 2 (minimum = 26, maximum = 56), 57% of Square 03.

The number of items trended upward throughout the sample period ( Fig 5(A)) . The largest spike occurred in context 6 with the appearance of the toiletry kit, which stored (and revealed) a number of related items. The kit can also be linked to one of the largest dips in item count, seen from contexts 52 to 53, when it was closed (but remained in the square). Other major changes can often be attributed to the addition and removal of bungee cords, which had other items such as carabiners and brackets attached. For example, the dip seen in context 25 correlates with the removal of a bungee cord with four carabiners.

(a) Count of artifacts and average count in Square 05 over time. (b) Proportions of artifacts by function in Square 05. Credit: Rao Hamza Ali.

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41 different item types were found in Square 05, about 55% as many as in Square 03. These belonged to five different categories: equipment (63%), electronic (17%), stowage (10%), office supplies (5%), and food (2%). The distribution of function proportions was quite different in this sample location ( Table 2 and Fig 5(B)) . Even though restraints were still most prominent, making up 32% of all items, body maintenance was almost as high (30%), indicating how strongly this area was associated with the activity of cleaning and caring for oneself. Computing (8%, represented by the laptop, which seems not to have been used), power (8%, from various cables), container (7%, resealable bags and Cargo Transfer Bags), and hygiene (6%, primarily the BPA duct) were the next most common items. Experiment was the function of 4% of the items, mostly the Touch Array, which appeared in every context, followed by drink (2%) and life support (1%). Safety, audiovisual, food, and light each made up less than 1% of the functional categories.

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Tracking changes over time is critical to understanding the activity happening in each area. We now explore how the assemblages change by calculating the Brainerd-Robinson Coefficient of Similarity [ 29 , 30 ] as operationalized by Peeples [ 31 , 32 ]. This metric is used in archaeology for comparing all pairs of the contexts by the proportions of categorical artifact data, here functional type. Applying the coefficient to the SQuARE contexts enables identification of time periods for distinct activities using artifact function and frequency alone, independent of documentary or oral evidence.

Multiple phases of activities took place in the square. Moments of connected activity are visible as red clusters in contexts 0–2, 11–12, 28–32, and 41 ( Fig 6(A)) . Combining this visualization with close observation of the photos themselves, we argue that there are actually eight distinct chronological periods.

• Contexts 0–2: Period 1 (S1 Fig in S3 File ) is a three-day period of work involving a portable glovebag (contexts 0–1) and a large blue stowage bag (context 2). It is difficult to describe trends in functional types because the glovebag and stowage bag obstruct the view of many objects. Items which appear at the top of the sample area, such as audiovisual and body maintenance items, are overemphasized in the data as a result. It appears that some kind of science is happening here, perhaps medical sample collection due to the presence of several small resealable bags visible in the glovebag. The work appears particularly intense in context 1, with the positioning of the video camera and light to point into the glovebag. These items indicate observation and oversight of crew activities by ground control. A white cargo transfer bag for storage and the stowage bag for holding packing materials in the context 2 photo likely relate to the packing of a Cargo Dragon vehicle that was docked to Node 2. The Dragon departed from the ISS for Earth, full of scientific samples, equipment, and crew personal items, a little more than three hours after the context 2 photo was taken [ 33 ].
• Contexts 3–10: Period 2 (S2 Fig in S3 File ) was a “stable” eight-day period in the sample, when little activity is apparent, few objects were moved or transferred in or out the square, and the primary function of the area seems to be storage rather than work. In context 6, a large Post-It notepad appeared in the center of the metal panel with a phone number written on it. This number belonged to another astronaut, presumably indicating that someone on the ISS had been told to call that colleague on the ground (for reasons of privacy, and in accordance with NASA rules for disseminating imagery, we have blurred the number in the relevant images). In context 8, the same notepad sheet had new writing appear on it, this time reading “COL A1 L1,” the location of an experimental rack in the European lab module.
• Contexts 11–12: Period 3 (S3 Fig in S3 File ) involves a second appearance of a portable glovebag (a different one from that used in contexts 0–1, according to its serial number), this time for a known activity, a concrete hardening experiment belonging to the European Space Agency [ 34 , 35 ]. This two-day phase indicates how the MWA space can be shared with non-US agencies when required. It also demonstrates the utility of this flexible area for work beyond biology/medicine, such as material science. Oversight of the crew’s activities by ground staff is evident from the positioning of the video camera and LED light pointing into the glovebag.
• Contexts 13–27: Period 4 (S4 Fig in S3 File ) is another stable fifteen-day period, similar to Period 2. Many items continued to be stored on the aluminum panel. The LED light’s presence is a trace of the activity in Period 3 that persists throughout this phase. Only in context 25 can a movement of the lamp potentially be connected to an activity relating to one of the stored items on the wall: at least one nitrile glove was removed from a resealable bag behind the lamp. In general, the primary identifiable activity during Period 4 is storage.
• Contexts 28–32: Period 5 (S5 Fig in S3 File ), by contrast, represents a short period of five days of relatively high and diverse activity. In context 28, a Microsoft Hololens augmented reality headset appeared. According to the DSR for the previous day, a training activity called Sidekick was carried out using the headset [ 36 ]. The following day, a Saturday, showed no change in the quantity or type of objects, but many were moved around and grouped by function—adhesive tape rolls were placed together, tools were moved from Velcro patches into pouches or straightened, and writing implements were placed in a vertical orientation when previously they were tilted. Context 29 represents a cleaning and re-organization of the sample area, which is a common activity for the crew on Saturdays [ 37 ]. Finally, in context 32, an optical coherence tomography scanner—a large piece of equipment for medical research involving crew members’ eyes—appeared [ 38 ]. This device was used previously during the sample period, but on the same day as the ESA concrete experiment, so that earlier work seems to have happened elsewhere [ 39 ].
• Contexts 33–40: Period 6 (S6 Fig in S3 File ) is the third stable period, in which almost no changes are visible over eight days. The only sign of activity is a digital timer which was started six hours before the context 39 image was made and continued to run at least through context 42.
• Context 41: Period 7 (S7 Fig in S3 File ) is a single context in which medical sample collection may have occurred. Resealable bags (some holding others) appeared in the center of the image and at lower right. One of the bags at lower right had a printed label reading “Reservoir Containers.” We were not able to discern which type of reservoir containers the label refers to, although the DSR for the day mentions “[Human Research Facility] Generic Saliva Collection,” without stating the location for this work [ 40 ]. Evidence from photos of other squares shows that labeled bags could be re-used for other purposes, so our interpretation of medical activity for this context is not conclusive.
• Contexts 42–60: Period 8 (S8 Fig in S3 File ) is the last and longest period of stability and low activity—eighteen days in which no specific activity other than the storage of items can be detected. The most notable change is the appearance for the first time of a foil water pouch in the central part of the blue panel.

Visualization of Brainerd-Robinson similarity, compared context-by-context by item function, for (a) Square 03 and (b) Square 05. The more alike a pair of contexts is, the higher the coefficient value, with a context compared against itself where a value of 200 equals perfect similarity. The resulting matrix of coefficients is visualized on a scale from blue to red where blue is lowest and red is highest similarity. The dark red diagonal line indicates complete similarity, where each context is compared to itself. Dark blue represents a complete difference. Credit: Shawn Graham.

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In the standards used at the time of installation, “stowage space” was the sixth design requirement listed for the MWA after accessibility; equipment size capability; scratch-resistant surfaces; capabilities for electrical, mechanical, vacuum, and fluid support during maintenance; and the accommodation of diagnostic equipment [ 20 ]. Only capabilities for fabrication were listed lower than stowage. Yet 50 of the 60 contexts (83%) fell within stable periods where little or no activity is identifiable in Square 03. According to the sample results, therefore, this area seems to exist not for “maintenance,” but primarily for the storage and arrangement of items. The most recent update of the design standards does not mention the MWA, but states, “Stowage location of tool kits should be optimized for accessibility to workstations and/or maintenance workbenches” [ 25 ]. Our observation confirms the importance of this suggestion.

The MWA was also a flexible location for certain science work, like the concrete study or crew health monitoring. Actual maintenance of equipment was hardly in evidence in the sample (possibly contexts 25, 39, and 44), and may not even have happened at all in this location. Some training did happen here, such as review of procedures for the Electromagnetic Levitator camera (instructions for changing settings on a high-speed camera appeared on the laptop screen; the day’s DSR shows that this camera is part of the Electromagnetic Levitator facility, located in the Columbus module [ 41 ]. The training required the use of the Hololens system (context 28 DSR, cited above).

Although many item types were represented in Square 03, it became clear during data capture how many things were basically static, unmoving and therefore unused, especially certain tools, writing implements, and body maintenance items. The MWA was seen as an appropriate place to store these items. It may be the case that their presence here also indicates that their function was seen as an appropriate one for this space, but the function(s) may not be carried out—or perhaps not in this location. Actualization of object function was only visible to us when the state of the item changed—it appeared, it moved, it changed orientation, it disappeared, or, in the case of artifacts that were grouped in collections rather than found as singletons, its shape changed or it became visibly smaller/lesser. We therefore have the opportunity to explore not only actuality of object use, but also potentiality of use or function, and the meaning of that quality for archaeological interpretation [ 42 , 43 ]. This possibility is particularly intriguing in light of the archaeological turn towards recognizing the agency of objects to impact human activity [ 44 , 45 ]. We will explore these implications in a future publication.

We performed the same chronological analysis for Square 05. Fig 6(B) represents the analysis for both item types and for item functions. We identified three major phases of activity, corresponding to contexts 0–5, 6–52, and 53–59 (S9-S11 Figs in S3 File ). The primary characteristics of these phases relate to an early period of unclear associations (0–5) marked by the presence of rolls of adhesive tape and a few body maintenance items (toothpaste and toothbrush, wet wipes); the appearance of a toiletry kit on the right side of the sample area, fully open with clear views of many of the items contained within (6–52); and finally, the closure of the toiletry kit so that its contents can no longer be seen (53–59). We interpret the phases as follows:

• Contexts 0–5: In Period 1 (six days, S9 Fig in S3 File ), while items such as a mirror, dental floss picks, wet wipes, and a toothbrush held in the end of a toothpaste tube were visible, the presence of various other kinds of items confounds easy interpretation. Two rolls of duct tape were stored on the handrail in the center of the sample area, and the Touch Array and laptop appeared in the center. Little movement can be identified, apart from a blue nitrile glove that appeared in context 1 and moved left across the area until it was wedged into the bungee cord for contexts 3 and 4. The tape rolls were removed prior to context 5. A collection of resealable bags was wedged behind the handrail in context 3, remaining there until context 9. Overall, this appears to be a period characterized by eclectic associations, showing an area without a clear designated function.
• Contexts 6–52: Period 2 (S10 Fig in S3 File ) is clearly the most significant one for this location due to its duration (47 days). It was dominated by the number of body maintenance items located in and around the toiletry kit, especially a white hand towel (on which a brown stain was visible from context 11, allowing us to confirm that the same towel was present until context 46). A second towel appeared alongside the toiletry kit in context 47, and the first one was fixed at the same time to the handrail, where it remained through the end of the sample period. A third towel appeared in context 52, attached to the handrail together with the first one by a bungee cord, continuing to the end of the sample period. Individual body maintenance items moved frequently from one context to the next, showing the importance of this type of activity for this part of Node 3. For reasons that are unclear, the mirror shifted orientation from vertical to diagonal in context 22, and then was put back in a vertical orientation in context 31 (a Monday, a day which is not traditionally associated with cleaning and organization). Collections of resealable bags appeared at various times, including a large one labeled “KYNAR BAG OF ZIPLOCKS” in green marker at the upper left part of the sample area beginning of context 12 (Kynar is a non-flammable plastic material that NASA prefers for resealable bags to the generic commercial off-the-shelf variety because it is non-flammable; however, its resistance to heat makes it less desirable for creating custom sizes, so bags made from traditional but flammable low-density polyethylene still dominate on the ISS [ 14 ]). The Kynar bag contained varying numbers of bags within it over time; occasionally, it appeared to be empty. The Touch Array changed orientation on seven of 47 days in period 2, or 15% of the time (12% of all days in the survey), showing activity associated with scientific research in this area. In context 49, a life-support item, the Airborne Particulate Monitor (APM) was installed [ 46 ]. This device, which measures “real-time particulate data” to assess hazards to crew health [ 47 ], persisted through the end of the sample period.
• Contexts 53–59: Period 3 (S11 Fig in S3 File ) appears as a seven-day phase marked by low activity. Visually, the most notable feature is the closure of the toiletry kit, which led to much lower counts of body maintenance items. Hardly any of the items on the wall moved at all during this period.

While body maintenance in the form of cleaning and caring for oneself could be an expected function for an area with exercise and excretion facilities, it is worth noting that the ISS provides, at most, minimal accommodation for this activity. A description of the WHC stated, “To provide privacy…an enclosure was added to the front of the rack. This enclosure, referred to as the Cabin, is approximately the size of a typical bathroom stall and provides room for system consumables and hygiene item stowage. Space is available to also support limited hygiene functions such as hand and body washing” [ 48 ]. A diagram of the WHC in the same publication shows the Cabin without a scale but suggests that it measures roughly 2 m (h) x .75 (w) x .75 (d), a volume of approximately 1.125 m 3 . NASA’s current design standards state that the body volume of a 95th percentile male astronaut is 0.99 m 3 [ 20 ], meaning that a person of that size would take up 88% of the space of the Cabin, leaving little room for performing cleaning functions—especially if the Cabin is used as apparently intended, to also hold “system consumables and hygiene item[s]” that would further diminish the usable volume. This situation explains why crews try to adapt other spaces, such as storage areas like the PMM, for these activities instead. According to the crew debriefing statement, only one of them used the WHC for body maintenance purposes; it is not clear whether the toiletry kit belonged to that individual. But the appearance of the toiletry kit in Square 05—outside of the WHC, in a public space where others frequently pass by—may have been a response to the limitations of the WHC Cabin. It suggests a need for designers to re-evaluate affordances for body maintenance practices and storage for related items.

Although Square 03 and 05 were different sizes and shapes, comparing the density of items by function shows evidence of their usage ( Table 3 ). The typical context in Square 03 had twice as many restraints and containers, but less than one-quarter as many body maintenance items as Square 05. 03 also had many tools, lights, audiovisual equipment, and writing implements, while there were none of any of these types in 05. 05 had life support and hygiene items which were missing from 03. It appears that flexibility and multifunctionality were key elements for 03, while in 05 there was emphasis on one primary function (albeit an improvised one, designated by the crew rather than architects or ground control), cleaning and caring for one’s body, with a secondary function of housing static equipment for crew hygiene and life support.

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As this is the first time such an analysis has been performed, it is not yet possible to say how typical or unusual these squares are regarding the types of activities taking place; but they provide a baseline for eventual comparison with the other four squares and future work on ISS or other space habitats.

Some general characteristics are revealed by archaeological analysis of a space station’s material culture. First, even in a small, enclosed site, occupied by only a few people over a relatively short sample period, we can observe divergent patterns for different locations and activity phases. Second, while distinct functions are apparent for these two squares, they are not the functions that we expected prior to this research. As a result, our work fulfills the promise of the archaeological approach to understanding life in a space station by revealing new, previously unrecognized phenomena relating to life and work on the ISS. There is now systematically recorded archaeological data for a space habitat.

Squares 03 and 05 served quite different purposes. The reasons for this fact are their respective affordances and their locations relative to activity areas designated for science and exercise. Their national associations, especially the manifestation of the control wielded by NASA over its modules, also played a role in the use of certain materials, the placement of facilities, and the organization of work. How each area was used was also the result of an interplay between the original plans developed by mission planners and habitat designers (or the lack of such plans), the utility of the equipment and architecture in each location, and the contingent needs of the crew as they lived in the station. This interplay became visible in the station’s material culture, as certain areas were associated with particular behaviors, over time and through tradition—over the long duration across many crews (Node 2, location of Square 03, docked with the ISS in 2007, and Node 3, location of Square 05, docked in 2010), and during the specific period of this survey, from January to March 2022. During the crew debriefing, one astronaut said, “We were a pretty organized crew who was also pretty much on the same page about how to do things…. As time went on…we organized the lab and kind of got on the same page about where we put things and how we’re going to do things.” This statement shows how functional associations can become linked to different areas of the ISS through usage and mutual agreement. At the same time, the station is not frozen in time. Different people have divergent ideas about how and where to do things. It seems from the appearance of just one Russian item—a packet of generic wipes ( salfetky sukhiye ) stored in the toiletry kit throughout the sample period—that the people who used these spaces and carried out their functions did not typically include the ISS’s Russian crew. Enabling greater flexibility to define how spaces can be used could have a significant impact on improving crew autonomy over their lives, such as how and where to work. It could also lead to opening of all spaces within a habitat to the entire crew, which seems likely to improve general well-being.

An apparent disjunction between planned and actual usage appeared in Square 03. It is intended for maintenance as well as other kinds of work. But much of the time, there was nobody working here—a fact that is not captured by historic photos of the area, precisely because nothing is happening. The space has instead become the equivalent of a pegboard mounted on a wall in a home garage or shed, convenient for storage for all kinds of items—not necessarily items being used there—because it has an enormous number of attachment points. Storage has become its primary function. Designers of future workstations in space should consider that they might need to optimize for functions other than work, because most of the time, there might not be any work happening there. They could optimize for quick storage, considering whether to impose a system of organization, or allow users to organize as they want.

We expected from previous (though unsystematic) observation of historic photos and other research, that resealable plastic bags (combined with Velcro patches on the bags and walls) would be the primary means for creating gravity surrogates to control items in microgravity. They only comprise 7% of all items in Square 03 (256 instances). There are more than twice as many clips (572—more than 9 per context) in the sample. There were 193 instances of adhesive tape rolls, and more than 100 cable ties, but these were latent (not holding anything), representing potentiality of restraint rather than actualization. The squares showed different approaches to managing “gravity.” While Square 03 had a pre-existing structured array of Velcro patches, Square 05 showed a more expedient strategy with Velcro added in response to particular activities. Different needs require different affordances; creating “gravity” is a more nuanced endeavor than it initially appears. More work remains to be done to optimize gravity surrogates for future space habitats, because this is evidently one of the most critical adaptations that crews have to make in microgravity (44% of all items in Square 03, 39% in 05).

Square 05 is an empty space, seemingly just one side of a passageway for people going to use the lifting machine or the latrine, to look out of the Cupola, or get something out of deep storage in one of the ISS’s closets. In our survey, this square was a storage place for toiletries, resealable bags, and a computer that never (or almost never) gets used. It was associated with computing and hygiene simply by virtue of its location, rather than due to any particular facilities it possessed. It has no affordances for storage. There are no cabinets or drawers, as would be appropriate for organizing and holding crew personal items. A crew member decided that this was an appropriate place to leave their toiletry kit for almost two months. Whether this choice was appreciated or resented by fellow crew members cannot be discerned based on our evidence, but it seems to have been tolerated, given its long duration. The location of the other four USOS crew members’ toiletry kits during the sample period is unknown. A question raised by our observations is: how might a function be more clearly defined by designers for this area, perhaps by providing lockers for individual crew members to store their toiletries and towels? This would have a benefit not only for reducing clutter, but also for reducing exposure of toiletry kits and the items stored in them to flying sweat from the exercise equipment or other waste particles from the latrine. A larger compartment providing privacy for body maintenance and a greater range of motion would also be desirable.

As the first systematic collection of archaeological data from a space site outside Earth, this analysis of two areas on the ISS as part of the SQuARE payload has shown that novel insights into material culture use can be obtained, such as the use of wall areas as storage or staging posts between activities, the accretion of objects associated with different functions, and the complexity of using material replacements for gravity. These results enable better space station design and raise new questions that will be addressed through analysis of the remaining four squares.

Supporting information

S1 movie. nasa astronaut kayla barron installs the first square for the sampling quadrangle assemblages research experiment in the japanese experiment module (also known as kibo) on the international space station, january 14, 2022..

She places Kapton tape to mark the square’s upper right corner. Credit: NASA.

https://doi.org/10.1371/journal.pone.0304229.s001

S1 Dataset.

https://doi.org/10.1371/journal.pone.0304229.s002

S2 Dataset.

https://doi.org/10.1371/journal.pone.0304229.s003

S3 Dataset. The image annotations are represented according to sample square in json formatted text files.

The data is available in the ‘SQuARE-notebooks’ repository on Github.com in the ‘data’ subfolder at https://github.com/issarchaeologicalproject/SQuARE-notebooks/tree/main ; archived version of the repository is at Zenodo, DOI: 10.5281/zenodo.10654812 .

https://doi.org/10.1371/journal.pone.0304229.s004

S1 File. The ‘Rocket-Anno’ image annotation software is available on Github at https://github.com/issarchaeologicalproject/MRE-RocketAnno .

The archived version of the repository is at Zenodo, DOI: 10.5281/zenodo.10648399 .

https://doi.org/10.1371/journal.pone.0304229.s005

S2 File. The computational notebooks that process the data json files to reshape the data suitable for basic statistics as well as the computation of the Brainerd-Robinson coefficients of similarity are in the.ipynb notebook format.

The code is available in the ‘SQuARE-notebooks’ repository on Github.com in the ‘notebooks’ subfolder at https://github.com/issarchaeologicalproject/SQuARE-notebooks/tree/main ; archived version of the repository is at Zenodo, DOI: 10.5281/zenodo.10654812 . The software can be run online in the Google Colab environment ( https://colab.research.google.com ) or any system running Jupyter Notebooks ( https://jupyter.org/ ).

https://doi.org/10.1371/journal.pone.0304229.s006

https://doi.org/10.1371/journal.pone.0304229.s007

Acknowledgments

We thank Chapman University’s Office of Research and Sponsored Programs, and especially Dr. Thomas Piechota and Dr. Janeen Hill, for funding the Implementation Partner costs associated with the SQuARE payload. Chapman’s Leatherby Libraries’ Supporting Open Access Research and Scholarship (SOARS) program funded the article processing fee for this publication. Ken Savin and Ken Shields at the ISS National Laboratory gave major support by agreeing to sponsor SQuARE and providing access to ISS NL’s allocation of crew time. David Zuniga and Kryn Ambs at Axiom Space were key collaborators in managing payload logistics. NASA staff and contractors were critical to the experiment’s success, especially Kristen Fortson, Jay Weber, Crissy Canerday, Sierra Wolbert, and Jade Conway. We also gratefully acknowledge the help and resources provided by Dr. Erik Linstead, director of the Machine Learning and Affiliated Technology Lab at Chapman University. Aidan St. P. Walsh corrected the color and lens barrel distortion in all of the SQuARE imagery. Rao Hamza Ali produced charts using accessible color combinations for Figs 3 and 5 . And finally, of course, we are extremely appreciative of the efforts of the five USOS members of the Expedition 66 crew on the ISS—Kayla Barron, Raja Chari, Thomas Marshburn, Matthias Maurer, and Mark Vande Hei—who were the first archaeologists in space.

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Mars Anomaly Research Society

You have reached the official website of the Mars Anomaly Research Society (MARS).

This is the web portal to receive news and information about the world's leading research, education, disclosure, and advocacy organization dedicated to fostering the study and protection of the ecology and civilization of Mars.

Featured Papers

• MARS - Basiago makes "Startling Discovery" of Striding Gremlin near Martian "Trees" - 1/17/10
• MARS - Andrew D. Basiago - Human Forms found in Glass Tubes on Mars - 10/31/09
• MARS - Andrew D. Basiago - The Face of a Pharaoh found on a Stone on Mars - 9/12/09
• MARS - Andrew D. Basiago - New Discovery - MARS IDs Transitional Phase of ID - 9/10/09
• MARS - Clif High identifies Andy as Planetary Whistle Blower predicted by ALTA - 9/18/09
• MARS - Andrew D. Basiago - The Discovery of Life on Mars - 12/12/08

Coast-to-Coast AM with George Noory, 11/11/09 Andrew D. Basiago: Project Pegasus

Introduction

Tonight, in a major disclosure event, the US time travel cover-up ends, as one of America’s early time-space explorers steps forward to reveal what he experienced and what he learned during the early years of time travel research and development by the United States government.

Our guest, Andrew D. Basiago, lawyer, writer, Mars researcher, and planetary whistle blower, brings his truth campaign to Coast-to-Coast AM, as he relates his childhood experiences in DARPA’s Project Pegasus, and shares with us the true history of the US time-space program.

Stay tuned, as tonight, we go in search of the past and the future, and discuss Project Pegasus, the real Philadelphia Experiment!

Andrew D. Basiago is a lawyer in private practice in Washington State, a writer, and a 21st century visionary.

He holds five academic degrees, including a BA in History from UCLA and a Master of Philosophy from the University of Cambridge.

Andy is an emerging figure in the Truth Movement, who is leading a campaign to lobby the United States government to disclose such controversial truths as the fact that Mars harbors life and that the United States has achieved “quantum access” to past and future events.

He has been identified as the first of two major planetary whistle blowers predicted by ALTA, the Web Bot project that analyzes the content of the World Wide Web to discern future trends.

Andy’s writings place him at the forefront of contemporary Mars research. His paper The Discovery of Life on Mars, published in 2008, was the first work to prove that Mars is an inhabited planet. After publishing his landmark paper, Andy founded the Mars Anomaly Research Society.

Andy is also one of America’s time travel pioneers. In the late 1960s and early 1970s, he was a child participant in the secret US time-space program, Project Pegasus.

He was the first American child to teleport and took part in probes to past and future events utilizing different forms of time travel then being researched and developed by DARPA.

For ten years, Andy has investigated his experiences in Project Pegasus on a quest to prove them and communicate them to others.

Next year, he will publish a tell-all book that will describe his awe-inspiring and terrifying experiences in Project Pegasus and the true story of the emergence of time travel in the US defense community 40 years ago.

Tonight, we will discuss Andy’s childhood experiences in Project Pegasus and his crusade as a lawyer to have the US government disclose its time travel secrets.

He will share with us the people, the places, the technologies, and the experiences that he encountered as a child time traveler in Project Pegasus, at the dawn of the time-space age!

Scientists lay out revolutionary method to warm Mars

Uchicago, northwestern study suggests new approach to warm mars could be 5,000 times more efficient than previous proposals.

Ever since we learned that the surface of planet Mars is cold and dead, people have wondered if there is a way to make it friendlier to life.

In a groundbreaking study published Aug. 7 in Science Advances , researchers from the University of Chicago, Northwestern University, and the University of Central Florida have proposed a revolutionary approach towards terraforming Mars. This new method, using engineered dust particles released to the atmosphere, could potentially warm the Red Planet by more than 50 degrees Fahrenheit, to temperatures suitable for microbial life—a crucial first step towards making Mars habitable.

The proposed method is over 5,000 times more efficient than previous schemes to globally warm Mars, representing a significant leap forward in our ability to modify the Martian environment.

What sets this approach apart is its use of resources readily available on Mars, making it far more feasible than earlier proposals that relied on importing materials from Earth or mining rare Martian resources.

This strategy would take decades. But it appears logistically easier than other plans proposed so far.

“This suggests that the barrier to warming Mars to allow liquid water is not as high as previously thought,” said Edwin Kite, an associate professor of geophysical sciences at the University of Chicago and corresponding author on the study. The lead author was Samaneh Ansari, a graduate student in Prof. Hooman Mohseni's group at Northwestern University.

Astronauts still won’t be able to breathe Mars' thin air; making the planet suitable for humans to walk on the surface unaided requires much more work. But perhaps groundwork could be laid, by making the planet habitable for microbes and food crops that could gradually add oxygen to the atmosphere—much as they have done for Earth during its geologic history.

A new approach to an age-old dream

There is a rich history of proposals to make Mars habitable; Carl Sagan himself came up with one back in 1971. These have ranged from outright daydreams, such as science fiction writers depicting turning one of Mars’ moons into a sun , to more recent and scientifically plausible ideas, such as engineering transparent gel tiles to trap heat .

Any plan to make Mars habitable must address several hurdles, including deadly UV rays and salty soil. But the biggest is the planet’s temperature; the surface of Mars averages about -80 degrees Fahrenheit.

One strategy to warm the planet could be the same method that humans are unintentionally using here on Earth: releasing material into the atmosphere, which would enhance Mars' natural greenhouse effect, trapping solar heat at the surface.

The trouble is that you would need tons of these materials—literally. Previous schemes depended on bringing gases from Earth to Mars, or attempting to mine Mars for a large mass of ingredients that aren’t very common there—both are costly and difficult propositions. But the team wondered whether it could be done by processing materials that already exist abundantly on Mars.

We know from rovers like Curiosity that dust on Mars is rich in iron and aluminum. By themselves, those dust particles aren’t suitable to warm the planet; their size and composition mean they tend to cool the surface slightly rather than warm it. But if we engineered dust particles that had different shapes or compositions, the researchers hypothesized, perhaps they could trap heat more efficiently.

The researchers designed particles shaped like short rods—similar in size to commercially available glitter. These particles are designed to trap escaping heat and scatter sunlight towards the surface, enhancing Mars' natural greenhouse effect.

“How light interacts with sub-wavelength objects is fascinating. Importantly, engineering nanoparticles can lead to optical effects that far exceed what is conventionally expected from such small particles,” said Ansari. Mohseni, who is a co-author, believes that they have just scratched the surface: “We believe it is possible to design nanoparticles with higher efficiency, and even those that can dynamically change their optical properties.”

“You'd still need millions of tons to warm the planet, but that’s five thousand times less than you would need with previous proposals to globally warm Mars,” said Kite. “This significantly increases the feasibility of the project.”

Calculations indicate that if the particles were released into Mars’ atmosphere continuously at 30 liters per second, the planet would warm by more than 50 degrees Fahrenheit—and the effect could be noticeable within as soon as months. Similarly, the warming would be reversible, stopping within a few years if release was switched off.

Potential impact and future research

Much work remains to be done, the scientists said. We don’t know exactly how fast the engineered dust would cycle out of Mars’ atmosphere, for example. Mars does have water and clouds, and, as the planet warms, it’s possible that water would increasingly start to condense around the particles and fall back to the surface as rain.

"Climate feedbacks are really difficult to model accurately," Kite cautioned. "To implement something like this, we would need more data from both Mars and Earth, and we'd need to proceed slowly and reversibly to ensure the effects work as intended."

While this method represents a significant leap forward in terraforming research, the researchers emphasize that the study focuses on warming Mars to temperatures suitable for microbial life and possibly growing food crops—not on creating a breathable atmosphere for humans.

“This research opens new avenues for exploration and potentially brings us one step closer to the long-held dream of establishing a sustainable human presence on Mars,” said Kite.

Other coauthors of the study were Ramses Ramirez of the University of Central Florida and Liam Steele, formerly a postdoctoral researcher at UChicago, now with the European Center for Medium-Range Weather Forecasts.

The authors used the Quest high-performance computing facility at Northwestern and the University of Chicago Research Computing Center.

Citation: “ Feasibility of keeping Mars warm with nanoparticles .” Ansari et al, Science Advances, August 7, 2024.

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