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Life on Mars: A Definite Possibility

Was Mars once a living world? Does life continue, even today, in a holding pattern, waiting until the next global warming event comes along? Many people would like to believe so. Scientists are no exception. But so far no evidence has been found that convinces even a sizable minority of the scientific community that the red planet was ever home to life. What the evidence does indicate, though, is that Mars was once a habitable world . Life, as we know it, could have taken hold there.

The discoveries made by NASA ’s Opportunity rover at Eagle Crater earlier this year (and being extended now at Endurance Crater) leave no doubt that the area was once ‘drenched’ in water . It might have been shallow water. It might not have stuck around for long. And billions of years might have passed since it dried up. But liquid water was there, at the martian surface, and that means that living organisms might have been there, too.

So suppose that Eagle Crater – or rather, whatever land formation existed in its location when water was still around – was once alive. What type of organism might have been happy living there?

Probably something like bacteria. Even if life did gain a foothold on Mars, it’s unlikely that it ever evolved beyond the martian equivalent of terrestrial single-celled bacteria. No dinosaurs; no redwoods; no mosquitoes – not even sponges, or tiny worms. But that’s not much of a limitation, really. It took life on Earth billions of years to evolve beyond single-celled organisms. And bacteria are a hardy lot. They are amazingly diverse, various species occupying extreme niches of temperature from sub-freezing to above-boiling; floating about in sulfuric acid; getting along fine with or without oxygen. In fact, there are few habitats on Earth where one or another species of bacterium can’t survive.

What kind of microbe, then, would have been well adapted to the conditions that existed when Eagle Crater was soggy? Benton Clark III , a Mars Exploration Rover ( MER ) science team member, says his “general favorite” candidates are the sulfate-reducing bacteria of the genus Desulfovibrio . Microbiologists have identified more than 40 distinct species of this bacterium.

Eating Rocks

We tend to think of photosynthesis as the engine of life on Earth. After all, we see green plants nearly everywhere we look and virtually the entire animal kingdom is dependent on photosynthetic organisms as a source of food. Not only plants, but many microbes as well, are capable of carrying out photosynthesis. They’re photoautotrophs: they make their own food by capturing energy directly from sunlight.

But Desulfovibrio is not a photoautotroph; it’s a chemoautotroph. Chemoautotrophs also make their own food, but they don’t use photosynthesis to do it. In fact, photosynthesis came relatively late in the game of life on Earth. Early life had to get its energy from chemical interactions between rocks and dirt, water, and gases in the atmosphere. If life ever emerged on Mars, it might never have evolved beyond this primitive stage.

Desulfovibrio makes its home in a variety of habitats. Many species live in soggy soils, such as marshes and swamps. One species was discovered all snug and cozy in the intestines of a termite. All of these habitats have two things in common: there’s no oxygen present; and there’s plenty of sulfate available.

Sulfate reducers, like all chemoautotrophs, get their energy by inducing chemical reactions that transfer electrons between one molecule and another. In the case of Desulfovibrio, hydrogen donates electrons, which are accepted by sulfate compounds. Desulfovibrio, says Clark, uses “the energy that it gets by combining the hydrogen with the sulfate to make the organic compounds” it needs to grow and to reproduce.

The bedrock outcrop in Eagle Crater is chock full of sulfate salts. But finding a suitable electron donor for all that sulfate is a bit more troublesome. “My calculations indicate [that the amount of hydrogen available is] probably too low to utilize it under present conditions,” says Clark. “But if you had a little bit wetter Mars, then there [would] be more water in the atmosphere, and the hydrogen gas comes from the water” being broken down by sunlight.

So water was present; sulfate and hydrogen could have as an energy source. But to survive, life as we know it needs one more ingredient carbon. Many living things obtain their carbon by breaking down the decayed remains of other dead organisms. But some, including several species of Desulfovibrio, are capable of creating organic material from scratch, as it were, drawing this critical ingredient of life directly from carbon dioxide (CO 2 ) gas. There’s plenty of that available on Mars.

All this gives reason to hope that life that found a way to exist on Mars back in the day when water was present. No one knows how long ago that was. Or whether such a time will come again. It may be that Mars dried up billions of years ago and has remained dry ever since. If that is the case, life is unlikely to have found a way to survive until the present.

Tilting toward Life

But Mars goes through cycles of obliquity, or changes in its orbital tilt. Currently, Mars is wobbling back and forth between 15 and 35 degrees’ obliquity, on a timescale of about 100,000 years. But every million years or so, it leans over as much as 60 degrees. Along with these changes in obliquity come changes in climate and atmosphere. Some scientists speculate that during the extremes of these obliquity cycles, Mars may develop an atmosphere as thick as Earth’s, and could warm up considerably. Enough for dormant life to reawaken.

“Because the climate can change on long terms,” says Clark, ice in some regions on Mars periodically could “become liquid enough that you would be able to actually come to life and do some things – grow, multiply, and so forth – and then go back to sleep again” when the thaw cycle ended. There are organisms on Earth that, when conditions become unfavorable, can form “spores which are so resistant that they can last for a very long time. Some people think millions of years, but that’s a little controversial.”

Desulfovibrio is not such an organism. It doesn’t form spores. But its bacterial cousin, Desulfotomaculum, does. “Usually the spores form because there’s something missing, like, for example, if hydrogen’s not available, or if there’s too much [oxygen], or if there’s not sulfate. The bacteria senses that the food source is going away, and it says, ‘I’ve got to hibernate,’ and will form the spores. The spores will stay dormant for extremely long periods of time. But they still have enough machinery operative that they can actually sense that nutrients are available. And then they’ll reconvert again in just a matter of hours, if necessary, to a living, breathing bacterium, so to speak. It’s pretty amazing,” says Clark.

That is not to say that future Mars landers should arrive with life-detection equipment tuned to zero in on species of Desulfovibrio or Desulfotomaculum. There is no reason to believe that life on Mars, if it ever emerged, evolved along the same lines as life on Earth, let alone that identical species appeared on the two planets. Still, the capabilities of various organisms on Earth indicate that life on Mars – including dormant organisms that could spring to life again in another few hundred thousand years – is certainly possible.

Clark says that he doesn’t “know that there’s any organism on Earth that could really operate on Mars, but over a long period of time, as the martian environment kept changing, what you would expect is that whatever life had started out there would keep adapting to the environment as it changed.”

Detecting such organisms is another matter. Don’t look for it to happen any time soon. Spirit and Opportunity were not designed to search for signs of life, but rather to search for signs of habitability. They could be rolling over fields littered with microscopic organisms in deep sleep and they’d never know it. Even future rovers will have a tough time identifying the martian equivalent of dormant bacterial spores.

“The spores themselves are so inert,” Clark says, “it’s a question, if you find a spore, and you’re trying to detect life, how do you know it’s a spore, [and not] just a little particle of sand? And the answer is: You don’t. Unless you can find a way to make the spore do what’s called germinating, going back to the normal bacterial form.” That, however, is a challenge for another day.

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Kate Howells • Feb 15, 2021

Life on Mars: Your Questions Answered

Is there life on Mars ? 

We humans have long been fascinated by this question. In 1895, astronomer Percival Lowel  mistakenly documented  what he believed were a series of artificial canals crisscrossing the planet. The idea that our neighboring planet might be home to intelligent beings captured imaginations around the world and spurred numerous visions of Mars , some peaceful and others malevolent. 

Fast-forward to the present day when humans have sent more spacecraft to study Mars than any other planet beyond Earth. To this day there is no evidence of life on Mars, but the search hasn’t stopped. Just as life itself evolves, so too have the ways we look for it. Today, the red planet is still a prime target in the search for life .

What is Mars like today?

Mars is on average inhospitably cold, with average temperatures of -63 ° C (-81 ° F). Summer highs occasionally reach 30°C (86° F), but it's still no picnic; the planet’s atmosphere is 95.3% carbon dioxide, and without a magnetic field its surface is bombarded by the Sun’s radiation. The low atmospheric pressure combined with cold temperatures also mean liquid water is not stable at the surface. Life as we know it cannot exist in these conditions. 

What was Mars like in the past?

Mars wasn't always this inhospitable to life. We think Mars once had a molten core that generated a magnetic field. This, in turn, protected the surface from radiation and supported a thicker atmosphere that kept the planet warm. 

There is also strong evidence that between 3 and 4 billion years ago , Mars had water on its surface. We can see valleys carved by rivers, pebbles that formed in streams, and piles of sediment that could have come from basins and deltas. Under these conditions, life could have been possible. 

About 3 billion years ago, Mars lost its protective magnetic field. Solar radiation stripped off most of the planet’s atmosphere , the liquid water disappeared, and Mars turned into the cold, dry desert we see today. 

Did life exist on Mars in the past?

Space missions like NASA’s Curiosity rover have determined that some portions of Mars were habitable for at least some periods of time long ago. But just because something could live there didn’t mean anything did. Without direct evidence of past life, we can't know whether Mars was ever inhabited. 

NASA’s Perseverance rover is searching for just that. It is exploring Jezero crater, a former lakebed and river delta, to look for ancient life immortalized in microscopic fossils. Perseverance is also stowing samples for future missions to return to Earth , where laboratories around the world will be able to study them in greater depth.

Does life exist on Mars now?

There is a slim chance that microbial life exists on Mars today, perhaps under the planet’s ice caps or in subsurface lakes detected by spacecraft like the European Space Agency’s Mars Express. Locations like these could protect life from the harsh conditions on the planet's surface. 

Because the kind of life that we think could exist on Mars today is microbial, it wouldn’t be spotted by the cameras of an orbiting spacecraft. Instead, there are ways we could detect it indirectly through chemical signatures linked to life called biosignatures. 

One such biosignature is methane, which can be created by both biological and geological processes. Curiosity has detected methane near its landing site in Gale Crater, but this isn't conclusive; the European Space Agency’s Trace Gas Express Orbiter has not found signs of the chemical in Mars’ atmosphere.

Could humans bring life to Mars?

When sending spacecraft to Mars to look for signs of life, it’s extremely important to make sure we don’t bring microbes along with us. Even though it takes months for a spacecraft to travel to Mars, hardy microorganisms could potentially survive the journey .

Every mission that lands on Mars must be thoroughly sterilized before it leaves Earth. Otherwise, instruments looking for signs of life might be fooled by life that came along with the spacecraft. Even worse, there is a slim but real possibility that Earthling microbes could survive and thrive on Mars, potentially interfering with any lifeforms that might already exist there.

The risk of contaminating Mars with Earthling microbes becomes even greater when considering future human missions to Mars. Human bodies are teeming with microbes, and it would be nearly impossible to contain them within a crewed Martian outpost. NASA, international space agencies, and private companies must work together to create planetary protection guidelines that balance the benefits of human exploration with the risk of contamination.

Could life on Earth have come from Mars?

We don’t know exactly how life on Earth began . The panspermia hypothesis suggests that life could have started elsewhere in the universe and traveled to Earth via asteroids, comets, and other small worlds . If Mars was indeed once home to life, it could have seeded our own planet with microbes embedded in Martian rocks that were knocked off the planet by another impactor.

A discovery in 1996 made panspermia seem particularly possible. Scientists studying a Martian meteorite known as ALH84001 found what looked like microbial fossils similar to ones found on Earth . Most experts ultimately agreed that alternative explanations for the structures were possible and that the meteorite was not a definitive indication of life. Nevertheless, the discovery arguably yielded a positive side effect: public excitement spurred investment in Mars research that continues to yield amazing discoveries today.

The Time is Now.

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Addressing the possibility of life on Mars

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In 2018, millions of people around the world caught glimpses of the planet Mars, discernible as a bright red dot in the summer’s night skies. Every 26 months or so, the red planet reaches a point in its elliptical orbit closest to Earth, setting the stage for exceptional visibility. This proximity also serves as an excellent opportunity for launching exploratory Mars missions, the next of which will occur in 2020 when a global suite of rovers will take off from Earth. 

The red planet was hiding behind the overcast, drizzling Boston sky on Oct. 11, when Mars expert John Grotzinger gave audiences a different perspective, taking them through an exploration of Mars' geologic history. Grotzinger, the Fletcher Jones Professor of Geology at the Caltech and a former professor in the MIT Department of Earth, Atmospheric and Planetary Sciences (EAPS), also used the eighth annual John Carlson Lecture to talk to the audience gathered at the New England Aquarium about the ongoing search for life on Mars.

Specializing in sedimentology and geobiology, Grotzinger has made significant contributions to understanding the early environmental history of the Earth and Mars and their habitability. In addition to involvement with the Mars Exploration Rover (MER) mission and the High Resolution Science Experiment (HiRISE) onboard the Mars Reconnaissance Orbiter (MRO), Grotzinger served as project scientist of the Mars Science Laboratory mission, which operates the Curiosity roving laboratory. Curiosity explores the rocks, soils, and air of the Gale Crater to find out whether Mars ever hosted an environment that was habitable for microbial life during its nearly 4.6-billion-year history.

“What I’d like to do is give you a very broad perspective of how we as scientists go about exploring a planet like Mars, with the rather audacious hypothesis that there could have been once life there,” he told the audience. “This is a classic mission of exploration where a team of scientists heads out into the unknown.”

“Simple one-celled microorganisms we know have existed on Earth for the last three-and-a-half billion years — a long time. They originated, they adapted, they evolved, and they didn’t change very much until you had the emergence of animals just 500 million years ago,” Grotzinger said. “For basically 3 billion years, the planet was pretty much alone with microbes. So, the question is: Could Mars have done something similar?”

Part of the research concerning whether or not Mars ever hosted ancient life involves identifying the environmental characteristics necessary for the survival of living organisms, including liquid water. Currently, the thin atmosphere around Mars prevents the accumulation of a standing body of water, but that may not always have been the case. Topographic features documented by orbiters and landers suggest the presence of ancient river channels, deltas and possibly even an ocean on Mars, “just like we see on Earth,” Grotzinger said. “This tells us that, at least, for some brief period of time if you want to be conservative, or maybe a long period of time, water was there [and] the atmosphere was denser. This is a good thing for life.”

To describe how scientists search for evidence of past habitability on Mars, Grotzinger told the story of stratigraphy — a discipline within geology that focuses on the sequential deposition and layering of sediments and igneous rocks. The changes that occur layer-to-layer indicate shifts in the environmental conditions under which different layers were deposited. In that manner, interpreting stratigraphic records is simple, he said.

“It’s like reading a book. You start at the bottom and you get to the first chapter, and you get to the top and you get to the last chapter,” Grotzinger said. “Sedimentary rocks are records of environmental change … what we want to do is explore this record on Mars.”

While Grotzinger and Curiosity both continue their explorations of Mars, scientists from around the world are working on pinpointing new landing sites for future Mars rovers which will expand the search for ancient life. This past summer, the SAM (Sample Analysis on Mars) instrument aboard the Curiosity rover detected evidence of complex organic matter in Gale Crater, a discovery which further supports the notion that Mars may have been habitable once.

“We know that Earth teems with life and we have enough of a fossil record to know that it’s been that way since we get to the oldest, well-preserved rocks on Earth. But yet, when you go to those rocks, you almost never find evidence of life,” Grotzinger said, leaving space for hope. “And that’s because, in the conversion of the sedimentary environment to the rock, there are enough mineralogic processes that are going on that the record of life gets erased. And so, I think we’re going to have to try over and over again.”

Following the lecture, members and friends of EAPS attended a reception in the main aquarium that featured some of the research currently taking place in the department. Posters and demonstrations were arranged around the aquarium’s cylindrical 200,000-gallon tank simulating a Caribbean coral reef, and attendees were able to chat with presenters and admire aquatic life while learning about current EAPS projects.

EAPS graduate student, postdoc, and research scientist presenters included Tyler Mackey, Andrew Cummings, Marjorie Cantine, Athena Eyster, Adam Jost, and Julia Wilcots from the Bergmann group; Kelsey Moore and Lily Momper from the Bosak group; Eric Beaucé, Ekaterina Bolotskaya, and Eva Golos from the Morgan group; Jonathan Lauderdale and Deepa Rao from the Follows group; Sam Levang from the Flierl group; Joanna Millstein and Kasturi Shah from the Minchew group; and Ainara Sistiaga, Jorsua Herrera, and Angel Mojarro from the Summons group.

The John H. Carlson Lecture series communicates exciting new results in climate science to general audiences. Free of charge and open to the general public, the annual lecture is made possible by a generous gift from MIT alumnus John H. Carlson to the Lorenz Center in the Department of Earth, Atmospheric and Planetary Sciences.

Anyone interested in join the invitation list for next year’s Carlson Lecture is encouraged to contact Angela Ellis .

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Signs of Life on Mars? NASA’s Perseverance Rover Begins the Hunt

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The robotic arm on NASA’s Perseverance rover reached out to examine rocks in an area on Mars nicknamed the “Cratered Floor Fractured Rough” area in this image captured on July 10, 2021 (the 138th sol, or Martian day, of its mission).

After testing a bristling array of instruments on its robotic arm, NASA’s latest Mars rover gets down to business: probing rocks and dust for evidence of past life.

NASA’s Mars 2020 Perseverance rover has begun its search for signs of ancient life on the Red Planet. Flexing its 7-foot (2-meter) mechanical arm, the rover is testing the sensitive detectors it carries, capturing their first science readings. Along with analyzing rocks using X-rays and ultraviolet light, the six-wheeled scientist will zoom in for closeups of tiny segments of rock surfaces that might show evidence of past microbial activity.

NASA’s Perseverance Mars rover took this close-up of a rock target nicknamed “Foux” using its WATSON camera on the end of the rover’s robotic arm. The image was taken July 11, 2021, the 139th Martian day, or sol, of the mission.

Called PIXL , or Planetary Instrument for X-ray Lithochemistry, the rover’s X-ray instrument delivered unexpectedly strong science results while it was still being tested, said Abigail Allwood, PIXL’s principal investigator at NASA’s Jet Propulsion Laboratory in Southern California. Located at the end of the arm, the lunchbox-size instrument fired its X-rays at a small calibration target – used to test instrument settings – aboard Perseverance and was able to determine the composition of Martian dust clinging to the target.

“We got our best-ever composition analysis of Martian dust before it even looked at rock,” Allwood said.

That’s just a small taste of what PIXL, combined with the arm’s other instruments, is expected to reveal as it zeroes in on promising geological features over the weeks and months ahead.

Scientists say Jezero Crater was a crater lake billions of years ago, making it a choice landing site for Perseverance. The crater has long since dried out, and the rover is now picking its way across its red, broken floor .

“If life was there in Jezero Crater, the evidence of that life could be there,” said Allwood, a key member of the Perseverance “arm science” team.

PIXL, one of seven instruments aboard NASA's Perseverance Mars rover, is equipped with light diodes circling its opening to take pictures of rock targets in the dark. Using artificial intelligence, PIXL relies on the images to determine how far away it is from a target to be scanned.

To get a detailed profile of rock textures, contours, and composition, PIXL’s maps of the chemicals throughout a rock can be combined with mineral maps produced by the SHERLOC instrument and its partner, WATSON. SHERLOC – short for Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals – uses an ultraviolet laser to identify some of the minerals in the rock, while WATSON takes closeup images that scientists can use to determine grain size, roundness, and texture, all of which can help determine how the rock was formed.

Early WATSON closeups have already yielded a trove of data from Martian rocks, the scientists said, such as a variety of colors, sizes of grains in the sediment, and even the presence of “cement” between the grains. Such details can provide important clues about formation history, water flow, and ancient, potentially habitable Martian environments. And combined with those from PIXL, they can provide a broader environmental and even historical snapshot of Jezero Crater.

“What is the crater floor made out of? What were the conditions like on the crater floor?” asks Luther Beegle of JPL, SHERLOC’s principal investigator. “That does tell us a lot about the early days of Mars, and potentially how Mars formed. If we have an idea of what the history of Mars is like, we’ll be able to understand the potential for finding evidence of life.”

This data shows chemicals detected within a single rock on Mars by PIXL, one of the instruments on the end of the robotic arm aboard NASA’s Perseverance Mars rover. PIXL allows scientists to study where specific chemicals can be found within an area as small as a postage stamp.

The Science Team

While the rover has significant autonomous capabilities, such as driving itself across the Martian landscape, hundreds of earthbound scientists are still involved in analyzing results and planning further investigations.

“There are almost 500 people on the science team,” Beegle said. “The number of participants in any given action by the rover is on the order of 100. It’s great to see these scientists come to agreement in analyzing the clues, prioritizing each step, and putting together the pieces of the Jezero science puzzle.”

That will be critical when the Mars 2020 Perseverance rover collects its first samples for eventual return to Earth. They’ll be sealed in superclean metallic tubes on the Martian surface so that a future mission could collect them and send back to the home planet for further analysis.

Despite decades of investigation on the question of potential life, the Red Planet has stubbornly kept its secrets.

“Mars 2020, in my view, is the best opportunity we will have in our lifetime to address that question,” said Kenneth Williford, the deputy project scientist for Perseverance.

The geological details are critical, Allwood said, to place any indication of possible life in context, and to check scientists’ ideas about how a second example of life’s origin could come about.

Combined with other instruments on the rover, the detectors on the arm, including SHERLOC and WATSON, could make humanity’s first discovery of life beyond Earth.

More About the Mission

A key objective for Perseverance’s mission on Mars is astrobiology , including the search for signs of ancient microbial life. The rover will characterize the planet’s geology and past climate, pave the way for human exploration of the Red Planet, and be the first mission to collect and cache Martian rock and regolith (broken rock and dust).

Subsequent NASA missions, in cooperation with ESA (European Space Agency), would send spacecraft to Mars to collect these sealed samples from the surface and return them to Earth for in-depth analysis.

The Mars 2020 Perseverance mission is part of NASA’s Moon to Mars exploration approach, which includes Artemis missions to the Moon that will help prepare for human exploration of the Red Planet.

JPL, which is managed for NASA by Caltech in Pasadena, California, built and manages operations of the Perseverance rover.

For more about Perseverance:

mars.nasa.gov/mars2020/

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Possible signs of Mars life: Astrobiologist explains Perseverance rover's exciting find

"This is not a slam dunk by any means — there's multiple lifetimes of questions to address."

The search for extraterrestrial life is as much about basic biology, geology and chemistry as it is about seeking to understand our place in the universe. The former came into the spotlight last month, when NASA's Perseverance rover found a rock with features and chemistry that could have been produced by ancient microbial life on Mars.

On July 21, the rover sampled an arrow-shaped rock, which scientists have nicknamed Cheyava Falls after the highest waterfall in Arizona's Grand Canyon, and found that it hosts organic compounds , which are the building blocks of life as we know it. Wisping through the length of the rock are veins of calcium sulfate, whose presence suggest a fluid — very likely water — once flowed through the rock. Finally, the rock is speckled with white spots with black rims, in which the rover's instruments detected iron phosphate molecules. On Earth, similar "leopard spots" are indicative of fossilized records of microbes. In the Cheyava Falls Mars rock, they may be signs of chemical reactions that occurred billions of years ago, which could have served as an energy source for ancient microbial life, the Perseverance science team shared in a NASA statement on July 25.

Taken together, these features are a potential biosignature — intriguing signs that the rock was once home to conditions typically linked to microbial life. While scientists on the Perseverance team are very excited about the rock, they stressed that they did not detect anything that could be fossilized organisms. It is also worth noting that the Perseverance rover isn't designed to detect and confirm alien life ; it's collecting samples of scientific interest that will be returned to Earth for further scrutiny.

Perhaps the Cheyava Falls rock could one day address a question that has existed for as long as humans have looked skyward: Are we alone in the universe ? 

Related: NASA's Perseverance Mars rover finds possible signs of ancient Red Planet life

The answer may very well land on Earth before the end of next decade, if NASA's troubled Mars Sample Return program pans out and delivers those precious samples home, where scientists can scrutinize them with a greater variety and complexity of instruments than Perseverance can carry.

"The discovery of life beyond Earth is so profound, so paradigm-shifting, you have to get it right," Amy Williams , an astrobiologist at the University of Florida who's on the Perseverance science team, told Space.com in a recent interview. "Once you cross that line, you can't come back."

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Space.com sat down with Williams to discuss what makes the Cheyava Falls sample so special, alternate explanations to alien life being considered by the mission team and the role Mars Sample Return would play in vetting the discovery.

The interview has been edited for length and clarity.

Space.com: What is it about Cheyava Falls that makes it so exciting in the search for alien life?

Amy Williams: This is the most compelling organics signal detection the rover has made so far. [The presence of organics] is always going to be a way for us to triage samples of interest; organic carbon makes up all life as we know it on Earth . But it's important to note that organic carbon can be made abiotically, i.e., without life. It can be made by geologic processes, and it's made on meteorites that were delivered to the surface of Mars over its history.

The leopard spots' texture is one of the things that can also help us identify a region or rock of interest. These spots are circular features of white mineral, and they've got a rim of a dark mineral around them. Using our instrument suite, we're able to determine it contains iron phosphate, and these kinds of features are often associated with microbial life on Earth. Seeing a texture like that, where you have these different redox phases in close proximity to each other, catches our attention, because that is the kind of thing that life could use as an energy source.

We often see calcium sulfate veins cross cutting across a variety of rocks on Mars. It might be that fluids were flowing through the rocks and they deposited those veins; we just drove up off of a delta fan structure, so we know that there was water here in the ancient past . 

All of these together are giving us this sense for an environment that was habitable in the ancient past, and some aspects of these features could be consistent with things we see on Earth that are associated with microbial life. That's why the excitement is here, and why we want to explore these rocks more.

Related: NASA's Perseverance rover confirms presence of ancient lake on Mars, and it may hold clues to past life

Space.com: Why can't Perseverance conclusively detect life on Mars?

Williams: The instrument suite onboard Perseverance is meant to triage samples for collection and return to Earth. There are no life-detection instruments onboard the rover.

There are a lot of parties that discuss what it would mean to have conclusive evidence for life on Mars . There are a lot of ways to approach it, and people want to be very conservative about it because once you cross that line, you can't come back. The discovery of life beyond Earth is so profound, so paradigm-shifting, you have to get it right. That's why it's so exciting to see a sample like this, because we have an opportunity to explore that space, to see if we found that evidence.

The instrument [suite] onboard Perseverance is not made to make that detection and confirmation; it's really the analyses that we can perform back on Earth. For the first time in our history of Mars exploration, we really have a good chance of being able to say something about whether there is evidence for ancient life on Mars or not.

Space.com: What's the mood like within the Perseverance team?

Williams: There's excitement in the team of finding something novel, whether or not there's evidence of life in this rock. It brings fresh energy to the team when we're working on something that has potential to reveal so much about Mars. There's always excitement when we collect a sample , and this sample in particular has been awe-inspiring — you take a moment to think about the amazing stuff that this team has been doing and NASA has been doing on Mars and other planetary bodies, so it's a cool time to step back and appreciate what we're all working toward.

Space.com: What alternate explanations is the team considering for the newfound features in the Cheyava Falls rock?

Williams: We're still trying to understand the environmental context for the rock in which this sample came from. For example, we found it close to where two rocks come together, and we're trying to understand that relationship. We don't know if these rocks were heated at all in the past — could that have driven any kind of rezoning of the elements? Nearby to those samples are these veins that contain a mineral called olivine — a big crystal made in magmas. Is that related to something that was way up the river valley and was brought in? Is it primary, in which case, how do you reconcile an environment that would be hot enough to have a magma but then also would have this organic carbon? If it were biologic, how do you reconcile that? These are questions that we are certainly grappling with now.

Our goal with the mission has always been to collect the most interesting samples for return to address these profound questions. This is not a slam dunk by any means. There's multiple lifetimes of questions to address.

Related: Possible sign of Mars life? Curiosity rover finds 'tantalizing' Red Planet organics

Space.com: What instruments on Earth could help us find ancient life on Mars?

Williams: We basically have every instrument that the global scientific community can lend. 

If you want to look at organic carbon, there are so many ways to detect organic carbon and to learn details about its structure that Perseverance doesn't have right now. You can do mass spectrometry analyzes to learn more about organic carbon present in that signal we're getting from SHERLOC [one of Perseverance's instruments]. Then, you have the potential to say something about the origin of that material: "This is so complex that maybe life made it because we don't know about abiotic process that can make it," or "This looks just like what you would see in a meteorite, [so] there's no reason that it would be been made by life," or [perhaps] you still cannot say either way. 

When you bring samples back, depending on what they're made of, we should be able to get ages on them. You can [then] tell something about when water was flowing on Mars. If we did think there was life, you can potentially be able to say how long ago it might have been there. There's all these paths you can go down and start to extrapolate. That's just on the astrobiology side of things — the tiniest wedge of things that I do and am excited about — but there's this whole pie of exciting science that we get to do with these samples if we can have them returned.

Space.com: We don't know what alien life looks like, so what would the search for it entail? For instance, would it be an elimination game where we rule out abiotic processes, or do we have a comprehensive catalog of signals from living organisms to tally the Cheyava Falls sample with?

Williams: The concept of life as we don't know it is always around the corner, and something that we should consider — even on a world that is seemingly as similar to Earth as Mars is.

What you're looking at is [whether] you see multiple lines of evidence that all point in either a biotic direction or an abiotic direction. In some ways, the most challenging answer would be both, because then it's still an ambiguous answer and you can't dissociate between the two. That is science.

Do we have a catalog of, "This is what biologic looks like, and this is what abiotic processes make?" Yes, and it's still evolving. I predict that if you bring a Mars sample home, scientific energy and research will turn in the direction of how you can separate out the gray areas of abiotic and biotic, and how we can refine how that space is determined to be able to say something specific about these extraordinary samples from Jezero Crater.

Related: Perseverance rover's Mars rock sample may contain best evidence of possible ancient life

— The search for alien life

— Perseverance rover's Mars rock sample may contain best evidence of possible ancient life

— Perseverance Mars rover digs into intriguing 'Bright Angel' rock formation (photo)

Space.com: How is the Perseverance rover doing? What's next for the mission?

Williams: I like to think that she's a happy rover, that she gets some joy from doing this. 

The rover is performing fantastic. We are finishing up the margin of Jezero Crater. Our plan has always been to climb out of the Jezero Crater and explore this really ancient Noachian terrain — one of the earliest time periods on Mars where there was water. Getting into a timeframe that we really haven't explored in situ before is extremely exciting.

It's great to have this excitement and momentum behind this. It makes everyone recognize the important contributions that we are making to the scientific community. It also gives me a lot of inspiration and hope about the kind of motivation for future scientists if these samples can come back. I just talked with a group of high schoolers, and I said, "You all are of the age where you can be the scientists working on these samples." That's incredible to me. 

These samples will be revolutionary. They're volumetrically small, but their importance dwarfs their size. So many future generations will learn extraordinary things about Earth from Mars, Mars about Mars, exoplanets … the list keeps going. There are questions we don't even know to ask yet that these samples give us the opportunity to do so.

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Sharmila Kuthunur is a Seattle-based science journalist covering astronomy, astrophysics and space exploration. Follow her on X @skuthunur.

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How We Land on Mars

Parachutes, airbags, heat shields— all these and more fill NASA's toolkit for getting spacecraft through the challenging, ultra-thin Martian atmosphere, then around mountains, cliffs, and rocks to a safe landing on the surface.

‘Seven Minutes of Terror’

The prospect of landing on Mars, long considered the stuff of science fiction, has become a reality over the past half century, thanks to human imagination, expertise, and persistence.

NASA has led the way with multiple missions that have landed safely on the Red Planet. Some of the landings have dispatched rovers to travel around the Martian surface, and some have served as stationary explorers, each gathering data and images from a specific landing site. They all have one thing in common: landing them on Mars requires intensive planning and expertise, to maximize the prospects of a safe and successful arrival. 

A whole host of things have to go precisely as planned for landing success. This tense process, known as Entry, Descent, and Landing, or EDL, has been referred to with such phrases as “seven minutes of terror.”

‘It is the result of reasoned engineering thought. But it still looks crazy.’

NASA engineers who designed the Curiosity Mars rover's entry, descent, and landing system talk candidly about its features, including a new element — the sky crane — and describe the challenges of the rover's final moments before touchdown.

Choosing How and Where to Land

“Each new lander or rover mission has presented new landing-system design challenges not faced by the ones that came before," said Rob Manning, an engineering fellow at NASA’s Jet Propulsion Laboratory in Southern California. Manning has worked on all NASA Mars rovers and landers since Pathfinder in 1997. 

"The Viking team had minimal landing-site information before sending the spacecraft to Mars. After their success, the next challenge was lowering the costs, which spawned the idea of using air bags for Mars Pathfinder, and that success then also enabled the Spirit and Opportunity rovers to land,” he said. After that, for Curiosity and Perseverance, “bigger rovers with grander capabilities, we had to invent the sky crane maneuver, and then new navigation techniques that enabled us to land at sites previously considered too risky."

When choosing a landing site, scientists conduct a rigorous pre-launch process to identify a location with terrain safe for landing, but with the right features to address mission goals of science discovery and help pave the way for future robotic missions, and potentially, future Mars astronauts. This “Mars in a Minute” video explains:

Stationary Landers

Viking 1 and viking 2.

The twin Vikings were the first two U.S. spacecraft to land safely on Mars. Each was transported separately to the Red Planet by its own orbiting spacecraft, which released the lander it was carrying when it was time to begin the landing process. Both landers touched down north of the Mars equator, with Viking 1 in Chryse Planitia, and Viking 2 in Utopia Planitia. Renowned astronomer Carl Sagan helped choose the landing sites. Viking 1 landed on Mars on July 20, 1976, followed by Viking 2 on Sept. 3, 1976. 

Each Viking had three triangular leg structures. Each leg was configured as an inverted tripod with three struts, and a skirted footpad. Once each orbiter was safely in orbit around Mars, the orbiter dropped the lander, and lifting aeroshells helped lengthen the entry, descent, and landing timeline. To slow the descent, the Vikings used the same type of parachutes we still use on Mars missions. Liquid-fueled, adjustable rocket engines were used for the final descent, while Doppler radars controlled the speed at crucial points in the landing process.

The Vikings' successful landings created a heritage adapted for future landers. While Mars Phoenix and Mars Insight appear to be closest to the Vikings' heritage, all the subsequent NASA Mars landers have been heavily influenced by the Viking design — from entry (heat shields), to descent (parachutes), terminal descent (radars), and landing.

Mars Phoenix Lander

The Mars Phoenix lander , designed to search for evidence of past or present microbial life, touched down in the Martian arctic area of Vastitas Borealis on May 25, 2008, using technologies inherited from the Viking spacecraft, with some upgrades. It was, in fact, the first successful landing of a stationary soft-lander on Mars since Viking 2 landed 32 years earlier.

Phoenix was designed with 12 on/off pulsed thrusters mounted around its bottom edge, to slow descent during the final 30 seconds before the legs touched the Martian surface.

Mars InSight

The Mars InSight Lander , which safely touched down on Mars' Elysium Planitia on Nov. 26, 2018, borrowed heavily from past NASA Mars missions, especially the Mars Phoenix Lander 10 years prior. But the entry, descent, and landing system was modified a bit for InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport): It used a thicker heat shield, partly because it was landing during dust-storm season — autumn in the Martian northern hemisphere. And its parachute suspension lines used stronger material.

Mars Landings With Rovers

Mars pathfinder.

July 4, 1997, had an especially exciting element added to the traditional fireworks and gatherings of America's Independence Day celebration. NASA's Mars Pathfinder spacecraft touched down on the Red Planet that day, toting humankind's first-ever Mars rover, Sojourner. The internet, still in its infancy, added an additional layer of interest, providing an opportunity for people around the world to watch fresh images from Mars and live feeds from mission control at NASA's Jet Propulsion Laboratory in Southern California, as history was made.

To land safely with its precious cargo, Pathfinder used a brand-new landing system, much different than its predecessors more than 20 years earlier, Vikings 1 and 2. As Pathfinder descended through the treacherous Martian atmosphere, a parachute and then rockets slowed the lander to a stop, dropping it about 66 feet (20 meters) above the Martian surface. This allowed a giant system of airbags to cushion the landing impact. Pathfinder bounced like a cluster of giant beach balls, more than 16 times and up to 50 feet (15 meters) high. Pathfinder stopped bouncing and settled on the Mars surface about 2½ minutes later, more than half a mile from the initial point of impact. Later, the world continued to watch excitedly as Pathfinder opened its ramp petals and the Sojourner rover rolled down onto the Mars surface.

Mars Exploration Rovers: Spirit and Opportunity

Inspired by the success of Pathfinder and Sojourner, NASA developed twin rovers, Spirit and Opportunity , to land on opposite sides of Mars on two different days — Spirit on Jan. 3, 2004, at Gusev Crater, and Opportunity on Jan. 24, 2004, at Meridiani Planum. The twin rovers used an entry, descent, and landing protocol nearly identical to that used by Pathfinder — with a lander assisted by a parachute, an aeroshell lowering the lander on a tether, firing rockets, inflated airbags to cushion the lander, and deployment of each rover rolling off its lander.

Mars Science Laboratory: Curiosity

The next generation of rovers — Mars Science Laboratory: Curiosity and Mars 2020: Perseverance — used existing entry, descent, and landing technologies, with a new addition. Both eliminated the use of air bags and added an innovative and daring element known as a sky crane. 

Due to the size and weight of these new, massive, science-laden rovers (more than a ton, or about 1,000 kilograms), an air bag-assisted landing would simply not be an option. Likewise, the complexity of getting a massive rover off a large-legged lander would make that choice too difficult and too heavy. Instead, engineers combined the best features of a propulsively controlled lander, like Viking, and the separation of the rover from the descent propulsion, used by Pathfinder, Spirit, and Opportunity. As a result, Curiosity and Perseverance used the sky crane maneuver. A new, separate, propulsive descent stage was placed above the rover to help guide the vehicle during entry, but also to serve as a payload delivery system, lowering the rover to the surface directly and softly onto its wheels. This method is very similar to the way helicopters maneuver heavy payloads on Earth.

On landing day, Aug. 5, 2012 PDT (Aug. 6 EDT), the sky crane maneuver lowered Curiosity to the Mars surface from the descent stage on three cables. This added element occurred during a crucial time, with only seven minutes to get from the top of the Martian atmosphere to the Mars surface — going from 13,000 mph to zero, with perfect sequence, choreography, and timing, all done autonomously by a computer. Thus, the name "Seven Minutes of Terror," as the mission engineers described the daring process required to deliver Curiosity safely to Gale Crater on Mars.

Mars 2020: Perseverance

For the Mars 2020 Perseverance rover , which landed Feb. 18, 2021 in Jezero Crater, engineers chose to reuse the sky crane system that had successfully landed the Curiosity rover in 2012. 

One additional factor came into play: The Jezero Crater landing site was in the most challenging Mars terrain ever targeted, with an ancient river delta, steep cliffs, sand dunes, boulder fields, and smaller impact craters. Landing in such a treacherous site required greater precision and a way to assure safe touchdown, with the reward of exploring an area that scientists believe may have been hospitable to ancient life.

Two new entry, descent, and landing technologies were needed.

The first addition was called Range Trigger. As the time during entry when parachute deployment neared, the onboard software autonomously updated the parachute deployment time based on its position. 

With the craft flying nearly sideways at supersonic speeds, the parachute could serve as a brake — when opened at the exact moment — to stop the horizontal motion precisely over the landing target. This trick enabled the science team to consider smaller, more precise, more daring landing sites such as Jezero Crater.

To find a safe place to land in a hazardous region, a second addition was needed. For the first time, a Mars lander needed to "look out the window" to figure out where it was on an onboard map. Enter another new technology: Terrain-Relative Navigation. It took pictures while descending to autonomously recognize Mars landmark features, estimate spacecraft position, and re-target the craft for precise, safe landing. The system also included the Lander Vision System, to capture and analyze a rapid series of photos to pinpoint the spacecraft's location, matching them to patterns in its map and helping to differentiate between safe sites and hazardous sites.

As Perseverance's descent stage slowed about 12 seconds and 66 feet (20 meters) above the Martian surface, it initiated the sky-crane maneuver. The descent stage lowered the rover on cables, and when the rover sensed that its wheels had touched the ground, it quickly cut the cables to the descent stage, which flew off to land at a safe distance from the rover.

The signals relaying all that took 11 minutes to reach the control room at NASA JPL. Then, amid the cheers and elation of her colleagues, Swati Mohan, the Mars 2020 guidance, navigation, and control operations lead announced to the world: “Touchdown confirmed. Perseverance safely on the surface of Mars, ready to begin seeking the signs of past life.”

‘Tango Delta. Touchdown confirmed!’

Views and commentary from mission control at NASA's Jet Propulsion Laboratory on Feb. 18, 2021, as the Mars 2020 Perseverance mission lands on Mars. Video includes footage from cameras on the spacecraft's entry, descent, and landing suite as it approached the Martian surface.

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Sean McMahon has received funding from Nasa.

The University of Edinburgh provides funding as a member of The Conversation UK.

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Nasa has announced the first detection of possible biosignatures in a rock on the surface of Mars. The rock contains the first martian organic matter to be decisively detected by the Perseverance rover , as well as curious discoloured spots that could indicate the past activity of microorganisms.

Ken Farley, project scientist on the mission, has called this “the most puzzling, complex, and potentially important rock yet investigated by Perseverance”.

Perseverance is part of Mars 2020, the first mission since Viking that is explicitly designed to seek life on Mars (officially, to “search for potential evidence of past life using observations regarding habitability and preservation as a guide”). Arguably, that objective has now been achieved: potential evidence for past life has been found. But much more work is needed to test this interpretation of the data. Here’s what we do know.

Since landing in Jezero crater a few years ago, Perseverance has traversed a series of rocks formed nearly four billion years before present. Mars back then was far more habitable than the cold, dry, toxic red planet of today.

There were thousands of rivers and lakes, a thick atmosphere, and comfortable temperatures and chemical conditions for life. Many of the rocks in Jezero are sedimentary: mud, silt and sand dumped by a river flowing into a lake.

The new discovery concerns one of these rocks. Informally named “Cheyava Falls” (a waterfall in Arizona), it is a small reddish block of what looks like a mudstone, enriched with organic molecules. The rock is also laced with parallel white veins. Between the veins are millimetre-scale whitish spots with dark rims. For an astrobiologist, all these features are intriguing. Let’s take them one-by-one.

First, “organic molecules” , are made of carbon and hydrogen (commonly with sulphur, oxygen or nitrogen as well). Examples include the proteins, fats, sugars, and nucleic acids from which all life as we know it is constructed.

Organic matter is common in rocks on Earth, most of it derived from the remains of ancient organisms. But the term “organic” is slightly misleading: such molecules can also be produced by non-biological reactions (in fact, we know this was happening four billion years ago on Mars).

Simple non-biological organic molecules are common in the universe, and Nasa’s Curiosity rover already found them in mudstones in Gale Crater. They were also reportedly detected by Perseverance in Jezero crater last year.

Nevertheless, Ken Farley considers the new observation the first truly “compelling detection” of organics made by Perseverance. Nasa has not told us which types of organic molecules are actually present in Cheyava Falls, so it is hard to evaluate their origins. They could turn out to be biological, but a full analysis using laboratories on Earth would be needed to settle this question.

Next, the veins. These are composed of calcium sulphate, which precipitated like limescale when liquid water ran along fractures in the subsurface. Veins like these are common in Martian sedimentary rocks (Curiosity saw plenty of them), and of course they are not “biosignatures” even though they normally represent habitable conditions.

My own work has shown that microorganisms inhabiting subsurface fractures can produce chemical fossils that get trapped in calcium sulphate veins. Strangely, however, the veins in Cheyava Falls also contain olivine, an igneous mineral. This might suggest that the water was injected at temperatures too high for life. We need more data to know one way or the other.

Finally, what about those whitish, discoloured spots? These look like the “reduction spots”, also called “leopard spots”, commonly seen in red sedimentary rocks on Earth. Such rocks are rusty-red because they contain an oxidised form of iron. When chemical reactions modify the iron to a less oxidised state, it becomes soluble. Water carries the pigment away leaving a bleached spot behind.

On Earth, these reactions are often driven by subsurface-dwelling bacteria. They use the oxidised iron as a source of energy, just as you and I use oxygen in the air. On Mars, bacteria-like organisms could have used the organic matter in the rock to complete the reaction (just as we use glucose from the food we eat).

Reduction spots haven’t been seen before on Mars, although bleached linear “halos” observed by Curiosity in Gale crater are somewhat similar. As one of the few astrobiologists to have studied reduction spots on Earth – and found evidence for biological processes within them – I am personally delighted. But as ever, caution is needed.

Potential non-biological causes need to be explored and ruled out. Iron-dissolving reactions can and do happen in sedimentary rocks without life. The dark margins of the Cheyava Falls spots are enriched in both iron and phosphate, an association previously suggested to occur around some calcium sulphate veins on Mars. This observation is consistent with life, but also with chemical reactions driven by acidic fluids.

The new findings will nevertheless embolden those calling on Nasa and the European Space Agency to proceed with the troubled multi-billion-dollar sample retrieval programme , which Perseverance was supposed to begin. The rover has now cored out a piece of the Cheyava Falls rock. If current plans are realised – a big if – then future spacecraft will collect this piece (and others) and bring it to Earth.

It will then be analysed in state-of-the-art laboratories far more capable than the instruments aboard Perseverance. Until that happens, we cannot be sure whether Perseverance has really found fossils of ancient life on Mars. The evidence so far is not definitive, but it is certainly tantalising.

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Life on Mars?

It’s hard enough to identify fossilized microbes on Earth. How would we ever recognize them on Mars?

Carl Zimmer

On August 7, 1996, reporters, photographers and television camera operators surged into NASA headquarters in Washington, D.C. The crowd focused not on the row of seated scientists in NASA’s auditorium but on a small, clear plastic box on the table in front of them. Inside the box was a velvet pillow, and nestled on it like a crown jewel was a rock—from Mars. The scientists announced that they’d found signs of life inside the meteorite. NASA administrator Daniel Goldin gleefully said it was an “unbelievable” day. He was more accurate than he knew.

The rock, the researchers explained, had formed 4.5 billion years ago on Mars, where it remained until 16 million years ago, when it was launched into space, probably by the impact of an asteroid. The rock wandered the inner solar system until 13,000 years ago, when it fell to Antarctica. It sat on the ice near AllanHills until 1984, when snowmobiling geologists scooped it up.

Scientists headed by David McKay of the JohnsonSpaceCenter in Houston found that the rock, called ALH84001, had a peculiar chemical makeup. It contained a combination of minerals and carbon compounds that on Earth are created by microbes. It also had crystals of magnetic iron oxide, called magnetite, which some bacteria produce. Moreover, McKay presented to the crowd an electron microscope view of the rock showing chains of globules that bore a striking resemblance to chains that some bacteria form on Earth. “We believe that these are indeed microfossils from Mars,” McKay said, adding that the evidence wasn’t “absolute proof” of past Martian life but rather “pointers in that direction.”

Among the last to speak that day was J. William Schopf, a University of California at Los Angeles paleobiologist, who specializes in early Earth fossils. “I’ll show you the oldest evidence of life on this planet,” Schopf said to the audience, and displayed a slide of a 3.465 billion-year-old fossilized chain of microscopic globules that he had found in Australia. “These are demonstrably fossils,” Schopf said, implying that NASA’s Martian pictures were not. He closed by quoting the astronomer Carl Sagan: “Extraordinary claims require extraordinary evidence.”

Despite Schopf’s note of skepticism, the NASA announcement was trumpeted worldwide. “Mars lived, rock shows Meteorite holds evidence of life on another world,” said the New York Times. “Fossil from the red planet may prove that we are not alone,” declared The Independent of London .

Over the past nine years, scientists have taken Sagan’s words very much to heart. They’ve scrutinized the Martian meteorite (which is now on view at the Smithsonian’s National Museum of Natural History), and today few believe that it harbored Martian microbes.

The controversy has prompted scientists to ask how they can know whether some blob, crystal or chemical oddity is a sign of life—even on Earth. Adebate has flared up over some of the oldest evidence for life on Earth, including the fossils that Schopf proudly displayed in 1996. Major questions are at stake in this debate, including how life first evolved on Earth. Some scientists propose that for the first few hundred million years that life existed, it bore little resemblance to life as we know it today.

NASA researchers are taking lessons from the debate about life on Earth to Mars. If all goes as planned, a new generation of rovers will arrive on Mars within the next decade. These missions will incorporate cutting-edge biotechnology designed to detect individual molecules made by Martian organisms, either living or long dead.

The search for life on Mars has become more urgent thanks in part to probes by the two rovers now roaming Mars’ surface and another spaceship that is orbiting the planet. In recent months, they’ve made a series of astonishing discoveries that, once again, tempt scientists to believe that Mars harbors life—or did so in the past. At a February conference in the Netherlands, an audience of Mars experts was surveyed about Martian life. Some 75 percent of the scientists said they thought life once existed there, and of them, 25 percent think that Mars harbors life today.

The search for the fossil remains of primitive single- celled organisms like bacteria took off in 1953, when Stanley Tyler, an economic geologist at the University of Wisconsin, puzzled over some 2.1 billion-year-old rocks he’d gathered in Ontario, Canada. His glassy black rocks known as cherts were loaded with strange, microscopic filaments and hollow balls. Working with Harvard paleobotonist Elso Barghoorn, Tyler proposed that the shapes were actually fossils, left behind by ancient life-forms such as algae. Before Tyler and Barghoorn’s work, few fossils had been found that predated the Cambrian Period, which began about 540 million years ago. Now the two scientists were positing that life was present much earlier in the 4.55 billion-year history of our planet. How much further back it went remained for later scientists to discover.

In the next decades, paleontologists in Africa found 3 billion- year-old fossil traces of microscopic bacteria that had lived in massive marine reefs. Bacteria can also form what are called biofilms, colonies that grow in thin layers over surfaces such as rocks and the ocean floor, and scientists have found solid evidence for biofilms dating back 3.2 billion years.

But at the time of the NASA press conference, the oldest fossil claim belonged to UCLA’s William Schopf, the man who spoke skeptically about NASA’s finds at the same conference. During the 1960s, ’70s and ’80s, Schopf had become a leading expert on early life-forms, discovering fossils around the world, including 3 billion-year-old fossilized bacteria in South Africa. Then, in 1987, he and some colleagues reported that they had found the 3.465 billion-yearold microscopic fossils at a site called Warrawoona in the Western Australia outback—the ones he would display at the NASA press conference. The bacteria in the fossils were so sophisticated, Schopf says, that they indicate “life was flourishing at that time, and thus, life originated appreciably earlier than 3.5 billion years ago.”

Since then, scientists have developed other methods for detecting signs of early life on Earth. One involves measuring different isotopes, or atomic forms, of carbon; the ratio of the isotopes indicates that the carbon was once part of a living thing. In 1996, a team of researchers reported that they had found life’s signature in rocks from Greenland dating back 3.83 billion years.

The signs of life in Australia and Greenland were remarkably old, especially considering that life probably could not have persisted on Earth for the planet’s first few hundreds of millions of years. That’s because asteroids were bombarding it, boiling the oceans and likely sterilizing the planet’s surface before about 3.8 billion years ago. The fossil evidence suggested that life emerged soon after our world cooled down. As Schopf wrote in his book Cradle of Life, his 1987 discovery “tells us that early evolution proceeded very far very fast.”

A quick start to life on Earth could mean that life could also emerge quickly on other worlds—either Earth-like planets circling other stars, or perhaps even other planets or moons in our own solar system. Of these, Mars has long looked the most promising.

The surface of Mars today doesn’t seem like the sort of place hospitable to life. It is dry and cold, plunging down as far as -220 degrees Fahrenheit. Its thin atmosphere cannot block ultraviolet radiation from space, which would devastate any known living thing on the surface of the planet. But Mars, which is as old as Earth, might have been more hospitable in the past. The gullies and dry lake beds that mark the planet indicate that water once flowed there. There’s also reason to believe, astronomers say, that Mars’ early atmosphere was rich enough in heat-trapping carbon dioxide to create a greenhouse effect, warming the surface. In other words, early Mars was a lot like early Earth. If Mars had been warm and wet for millions or even billions of years, life might have had enough time to emerge. When conditions on the surface of Mars turned nasty, life may have become extinct there. But fossils may have been left behind. It’s even possible that life could have survived on Mars below the surface, judging from some microbes on Earth that thrive miles underground.

When Nasa’s Mckay presented his pictures of Martian fossils to the press that day in 1996, one of the millions of people who saw them on television was a young British environmental microbiologist named Andrew Steele. He had just earned a PhD at the University of Portsmouth, where he was studying bacterial biofilms that can absorb radioactivity from contaminated steel in nuclear facilities. An expert at microscopic images of microbes, Steele got McKay’s telephone number from directory assistance and called him. “I can get you a better picture than that,” he said, and convinced McKay to send him pieces of the meteorite. Steele’s analyses were so good that soon he was working for NASA.

Ironically, though, his work undercut NASA’s evidence: Steele discovered that Earthly bacteria had contaminated the Mars meteorite. Biofilms had formed and spread through cracks into its interior. Steele’s results didn’t disprove the Martian fossils outright—it’s possible that the meteorite contains both Martian fossils and Antarctic contaminants— but, he says, “The problem is, how do you tell the difference?” At the same time, other scientists pointed out that nonliving processes on Mars also could have created the globules and magnetite clumps that NASA scientists had held up as fossil evidence.

But McKay stands by the hypothesis that his microfossils are from Mars, saying it is “consistent as a package with a possible biological origin.” Any alternative explanation must account for all of the evidence, he says, not just one piece at a time.

The controversy has raised a profound question in the minds of many scientists: What does it take to prove the presence of life billions of years ago? in 2000, oxford paleontologistMartin Brasier borrowed the original Warrawoona fossils from the NaturalHistoryMuseum in London, and he and Steele and their colleagues have studied the chemistry and structure of the rocks. In 2002, they concluded that it was impossible to say whether the fossils were real, essentially subjecting Schopf’s work to the same skepticism that Schopf had expressed about the fossils from Mars. “The irony was not lost on me,” says Steele.

In particular, Schopf had proposed that his fossils were photosynthetic bacteria that captured sunlight in a shallow lagoon. But Brasier and Steele and co-workers concluded that the rocks had formed in hot water loaded with metals, perhaps around a superheated vent at the bottom of the ocean—hardly the sort of place where a sun-loving microbe could thrive. And microscopic analysis of the rock, Steele says, was ambiguous, as he demonstrated one day in his lab by popping a slide from the Warrawoona chert under a microscope rigged to his computer. “What are we looking at there?” he asks, picking a squiggle at random on his screen. “Some ancient dirt that’s been caught in a rock? Are we looking at life? Maybe, maybe. You can see how easily you can fool yourself. There’s nothing to say that bacteria can’t live in this, but there’s nothing to say that you are looking at bacteria.”

Schopf has responded to Steele’s criticism with new research of his own. Analyzing his samples further, he found that they were made of a form of carbon known as kerogen, which would be expected in the remains of bacteria. Of his critics, Schopf says, “they would like to keep the debate alive, but the evidence is overwhelming.”

The disagreement is typical of the fast-moving field. Geologist Christopher Fedo of George Washington University and geochronologist Martin Whitehouse of the Swedish Museum of Natural History have challenged the 3.83 billionyear- old molecular trace of light carbon from Greenland, saying the rock had formed from volcanic lava, which is much too hot for microbes to withstand. Other recent claims also are under assault. Ayear ago, a team of scientists made headlines with their report of tiny tunnels in 3.5 billion-year-old African rocks. The scientists argued that the tunnels were made by ancient bacteria around the time the rock formed. But Steele points out that bacteria might have dug those tunnels billions of years later. “If you dated the London Underground that way,” says Steele, “you’d say it was 50 million years old, because that’s how old the rocks are around it.”

Such debates may seem indecorous, but most scientists are happy to see them unfold. “What this will do is get a lot of people to roll up their sleeves and look for more stuff,” says MIT geologist John Grotzinger. To be sure, the debates are about subtleties in the fossil record, not about the existence of microbes long, long ago. Even a skeptic like Steele remains fairly confident that microbial biofilms lived 3.2 billion years ago. “You can’t miss them,” Steele says of their distinctive weblike filaments visible under a microscope. And not even critics have challenged the latest from Minik Rosing, of the University of Copenhagen’s Geological Museum, who has found the carbon isotope life signature in a sample of 3.7 billion-year-old rock from Greenland—the oldest undisputed evidence of life on Earth.

At stake in these debates is not just the timing of life’s early evolution, but the path it took. This past September, for example, Michael Tice and Donald Lowe of StanfordUniversity reported on 3.416 billion-year-old mats of microbes preserved in rocks from South Africa. The microbes, they say, carried out photosynthesis but didn’t produce oxygen in the process. A small number of bacterial species today do the same—anoxygenic photosynthesis it’s called—and Tice and Lowe suggest that such microbes, rather than the conventionally photosynthetic ones studied by Schopf and others, flourished during the early evolution of life. Figuring out life’s early chapters will tell scientists not only a great deal about the history of our planet. It will also guide their search for signs of life elsewhere in the universe—starting with Mars.

In January 2004, the NASA rovers Spirit and Opportunity began rolling across the Martian landscape. Within a few weeks, Opportunity had found the best evidence yet that water once flowed on the planet’s surface. The chemistry of rock it sampled from a plain called Meridiani Planum indicated that it had formed billions of years ago in a shallow, long-vanished sea. One of the most important results of the rover mission, says Grotzinger, a member of the rover science team, was the robot’s observation that rocks on Meridiani Planum don’t seem to have been crushed or cooked to the degree that Earth rocks of the same age have been— their crystal structure and layering remain intact. A paleontologist couldn’t ask for a better place to preserve a fossil for billions of years.

The past year has brought a flurry of tantalizing reports. An orbiting probe and ground-based telescopes detected methane in the atmosphere of Mars. On Earth, microbes produce copious amounts of methane, although it can also be produced by volcanic activity or chemical reactions in the planet’s crust. In February, reports raced through the media about a NASA study allegedly concluding that the Martian methane might have been produced by underground microbes. NASA headquarters quickly swooped in—perhaps worried about a repeat of the media frenzy surrounding the Martian meteorite—and declared that it had no direct data supporting claims for life on Mars.

But just a few days later, European scientists announced that they had detected formaldehyde in the Martian atmosphere, another compound that, on Earth, is produced by living things. Shortly thereafter, researchers at the European Space Agency released images of the Elysium Plains, a region along Mars’ equator. The texture of the landscape, they argued, shows that the area was a frozen ocean just a few million years ago—not long, in geological time. Afrozen sea may still be there today, buried under a layer of volcanic dust. While water has yet to be found on Mars’ surface, some researchers studying Martian gullies say that the features may have been produced by underground aquifers, suggesting that water, and the life-forms that require water, might be hidden below the surface.

Andrew Steele is one of the scientists designing the next generation of equipment to probe for life on Mars. One tool he plans to export to Mars is called a microarray, a glass slide onto which different antibodies are attached. Each antibody recognizes and latches onto a specific molecule, and each dot of a particular antibody has been rigged to glow when it finds its molecular partner. Steele has preliminary evidence that the microarray can recognize fossil hopanes, molecules found in the cell walls of bacteria, in the remains of a 25 million- year-old biofilm.

This past September, Steele and his colleagues traveled to the rugged Arctic island of Svalbard, where they tested the tool in the area’s extreme environment as a prelude to deploying it on Mars. As armed Norwegian guards kept a lookout for polar bears, the scientists spent hours sitting on chilly rocks, analyzing fragments of stone. The trip was a success: the microarray antibodies detected proteins made by hardy bacteria in the rock samples, and the scientists avoided becoming food for the bears.

Steele is also working on a device called MASSE (Modular Assays for Solar System Exploration), which is tentatively slated to fly on a 2011 European Space Agency expedition to Mars. He envisions the rover crushing rocks into powder, which can be placed into MASSE, which will analyze the molecules with a microarray, searching for biological molecules.

Sooner, in 2009, NASA will launch the Mars Science Laboratory Rover. It’s designed to inspect the surface of rocks for peculiar textures left by biofilms. The Mars lab may also look for amino acids, the building blocks of proteins, or other organic compounds. Finding such compounds wouldn’t prove the existence of life on Mars, but it would bolster the case for it and spur NASA scientists to look more closely.

Difficult as the Mars analyses will be, they’re made even more complex by the threat of contamination. Mars has been visited by nine spacecraft, from Mars 2, a Soviet probe that crashed into the planet in 1971, to NASA’s Opportunity and Spirit. Any one of them might have carried hitchhiking Earth microbes. “It might be that they crash-landed and liked it there, and then the wind could blow them all over the place,” says Jan Toporski, a geologist at the University of Kiel, in Germany. And the same interplanetary game of bumper cars that hurtled a piece of Mars to Earth might have showered pieces of Earth on Mars. If one of those terrestrial rocks was contaminated with microbes, the organisms might have survived on Mars—for a time, at least—and left traces in the geology there. Still, scientists are confident they can develop tools to distinguish between imported Earth microbes and Martian ones.

Finding signs of life on Mars is by no means the only goal. “If you find a habitable environment and don’t find it inhabited, then that tells you something,” says Steele. “If there is no life, then why is there no life? The answer leads to more questions.” The first would be what makes life-abounding Earth so special. In the end, the effort being poured into detecting primitive life on Mars may prove its greatest worth right here at home.

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The 5 possibilities for life on mars.

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While Mars is known as a frozen, red planet today, it has all the evidence we could ask for of a ... [+] watery past, lasting for approximately the first 1.5 billion years of the Solar System. Could it have been Earth-like, even to the point of having had life on it, for the first third of our Solar System's history?

For as long as humanity has been watching the skies, we’ve been fascinated with the possibility that other worlds — much like Earth — might contain living organisms. While our visits to the Moon taught us that it’s completely barren and uninhabited, other worlds within our Solar System remain full of potential. Venus might have life in its cloud-tops . Europa and Enceladus might have life teeming in a sub-surface ocean of liquid water. Even Titan’s liquid hydrocarbon lakes provide a fascinating place to search for exotic living organisms.

But by far, the most fascinating possibility is the red planet: Mars. This smaller, colder, more distant cousin of Earth most certainly had a wet past, where liquid water clearly flowed on the surface for more than a billion years. Circumstantial evidence has pointed to the plausibility of life on Mars, not only in the ancient past, but possibly still living, and perhaps occasionally active, even today. There are five possibilities for life on Mars. Here’s what we know so far.

Oxbow bends only occur in the final stages of a slowly flowing river's life, and this one is found ... [+] on Mars. While many of Mars's channel-like features originate from a glacial past, there is ample evidence of a history of liquid water on the surface, such as this dried-up riverbed.

With the information we’ve obtained from various orbiters, landers, and rovers, we’ve made a slew of fascinating discoveries on Mars. We see dried-up riverbeds and evidence of ancient glacial events on the Martian surface. We find tiny hematite spheres on Mars as well as copious evidence for sedimentary rock, both of which only form on Earth in aqueous environments. And we’ve observed solid sub-surface ice, snows, and even frozen surface water on Mars in real-time.

We’ve even observed what’s likely to be briny surface water actively flowing down the walls of various craters, although that result is still controversial. All the raw ingredients that are required for life on Earth were abundant on early Mars as well, including a thick atmosphere and liquid water on its surface. Although Mars no longer appears as though it’s teeming with life today, there are three pieces of evidence that past or even present life might be a possibility.

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The hematite spheres (or 'Martian blueberries') as imaged by the Mars Exploration Rover. These are ... [+] almost certainly evidence of past liquid water on Mars, and possibly of past life. NASA scientists must be certain that this site -- and this planet -- are not contaminated by the very act of our observing. As of yet, there is no surefire evidence for either past or present Martian life.

The first compelling piece of evidence came from the instruments on board NASA’s Mars Viking landers in 1976. There were three biology experiments performed: a gas exchange experiment, a labeled release experiment, and a pyrolytic release experiment, followed-up by a gas chromatograph mass spectrometer experiment. The labeled release experiment yielded a positive result when performed on both Viking landers, but only the first time the test occurred. All other experiments came back negative.

The second piece of evidence came when a fragment of a Martian meteorite — Allan Hills 84001 — was recovered on December 27, 1984. As it turns out, approximately 3% of all meteorites that fall to Earth originate from Mars, but this one was particularly large: nearly 2 kilograms (over 4 pounds) heavy. It originally formed on Mars some 4 billion years ago, and landed on Earth only some 13,000 years ago. When we looked inside of it in 1996, it appears to contain material that could be the remnants of fossilized organic life forms , although they could have arisen from inorganic processes as well.

Most recently, the Mars Curiosity rover detected Methane vents on Mars, which could have been ... [+] produced either organically or inorganically. If it's organics, the author will lose a bet with physicist Robert Garisto!

And finally, the third piece of evidence came out with NASA’s latest Mars rover: Curiosity. As the seasons changed on Mars, Curiosity detected “burps” of methane emitted from specific underground locations, but only at the end of Martian winter and with the onset of spring. This is, again, an ambiguous signal at best, as inorganic, geochemical processes could be seasonal and result in the release of methane, but organic, biological processes could cause this as well.

When we look at the full suite of evidence — at everything we’ve learned about Mars — there are five possibilities for the history of life on the Red Planet. It could be an eternally barren world; it could be a world where life thrived for a time but then hit a dead-end; it could have extant life on it today; it could have been seeded by Earth life early on; or it could only have Earth-based organisms that made their way there since the dawn of the space age.

Here’s what each possibility would mean.

Mars, along with its thin atmosphere, as photographed from the Viking orbiter. From afar as well as ... [+] up close, there are no obvious, compelling signs of past or present life on the planet, although there are some ambiguous points that could either favor or disfavor life.

1.) Mars never had life on it . Despite having the same raw ingredients as early Earth and similar, watery conditions, the necessary circumstances that enable life to form simply never occurred on Mars. All the geological and chemical processes that occur inorganically still happened, but nothing organic. Then, a little more than three billion years ago, Mars’s atmosphere was stripped away by the Sun, drying up any liquid surface water and leading to Mars’s current appearance.

This is the most conservative stance, and would require that all three of the purported “positive” tests have either an inorganic or contamination-based resolution. This is eminently possible, and remains — in the mind of many — the default assumption. Until some very compelling evidence comes along that robustly points to either past or present life on Mars, this will likely remain the leading hypothesis.

Seasonal frozen lakes appear throughout Mars, showing evidence of (not liquid) water on the surface. ... [+] These are just a few of the many lines of evidence that point to a watery past on Mars. Whether water indicates life or not has not yet been determined.

2.) Mars had life early on, but it died out . This scenario, in many ways, is just as compelling as the prior one. It’s very easy to imagine that a world with:

• a thick atmosphere similar to early Earth’s,
• stable, liquid water on its surface,
• continents with rich geological diversity,
• a magnetic field,
• a day similar in length to our own,
• and temperatures only marginally cooler than Earth’s today,

could lead to life. To many, it’s virtually impossible to imagine that these conditions — after more than a billion years — wouldn’t lead to life, considering that life arose on Earth no more than a few hundred million years after its formation.

However, the loss of the Martian atmosphere had a profound effect on the planet, and could have resulted in the extinction of all life on Mars. Drilling down into the sedimentary rock of Mars and searching for fossilized life forms, or even metamorphosed carbon-rich inclusions, could potentially reveal the evidence necessary to validate this scenario.

Recurring slope lineae, like this one on the south-facing slope of a crater on the floor of Melas ... [+] Chasma, have not only been shown to grow over time and then fade away as the martian landscape fills them in with dust, but are known to be caused by the flowing of briny, liquid water. Perhaps, in those flows, life processes are occurring.

3.) Mars had early life, and it still persists in a mostly-dormant form beneath the surface . This is the most optimistic, but still scientifically viable, view of life on Mars. Perhaps life took hold early on, and when Mars lost its atmosphere, a few extremophiles remained in a sort of frozen, suspended-animation state. When the right conditions emerged — perhaps underground, where liquid water can occasionally flow — that life “wakes up” and begins performing its critical biological functions.

If this is the case, then there are still organisms to be found beneath the Martian surface, perhaps in the shallow sands just a few feet or even mere inches below our spacecraft. We’re likely only talking about single-celled life, perhaps not even reaching the complexity of a eukaryotic cell, but life on any world other than Earth would still be a revolution for science. NASA’s Perseverance rover, which launched successfully on July 30, 2020 , will collect critical soil samples to attempt to test this hypothetical scenario.

A planetoid colliding with Earth, larger than even the asteroid strike that wiped out the dinosaurs, ... [+] could easily kick up sufficient amounts of material that some of it would make it to Mars, possibly contaminating the ancient Red Planet with Earth-like material, as well as Earth-based biological organisms.

4.) Mars didn’t have life until Earth seeded it, naturally . 65 million years ago, a very large, fast-moving body impacted Earth, creating Chixulub crater and kicking up enough material to blanket the Earth in a cloud of debris, leading to the fifth great mass extinction in Earth’s history. And, like many massive impacts, this one likely kicked up small pieces of Earth all the way into space, the same way that impactors on the Moon or Mars send meteors throughout the Solar System, where some of them eventually land on Earth.

Well, a few impacts likely go the other way as well: sending Earth-borne material to other worlds, including Mars. It seems unreasonable that the material in Earth’s crust, rich in organic life, wouldn’t make it to Mars at all. Instead, it’s eminently plausible that Earth-based organisms made it to Mars and began reproducing there, whether they thrived or not. Perhaps someday, we’ll be able to know the full history of life on Mars, and determine whether any of it has the same common ancestor that all extant Earth life is descended from. It’s a fascinating possibility that isn’t easy to dismiss.

The first truly successful landers, Viking 1 and 2, returned data and images for years, including ... [+] providing a controversial signal that may have indicated life's presence on the red planet.

5.) Our modern space program spread Earth-based life to Mars . And, finally, perhaps Mars truly was a barren, lifeless planet — at least for billions of years — until the dawn of the space age. Perhaps spaceborne materials that weren’t 100% decontaminated or sterilized landed on the Martian surface, bringing modern Earth organisms with them as stowaways.

It’s the ultimate nightmare of astrobiologists: that there’s a fascinating history of life to uncover on another world, but we’ll contaminate it with our own organisms before we ever learn the true history of life on that world. In the worst case scenario, it could be the case that was surviving simple life on Mars of Martian origin, but that Earth life arrived and out-competed it, driving it to a rapid extinction. This very real, healthy fear is why we’re frequently so conservative, from a biological perspective, when we explore other planets and foreign worlds.

An Atlas V rocket with NASA's Perseverance Mars rover launches from pad 41 at Cape Canaveral Air ... [+] Force Station. The Mars 2020 mission plans to land the Perseverance rover on the Red Planet in February 2021, where it will seek signs of ancient life and collect rock and soil samples for possible return to Earth. (Paul Hennessy/SOPA Images/LightRocket via Getty Images)

There is a tremendous hope that current and future generations of Mars rovers and orbiters will help us finally puzzle out whether Mars — either now or at any point in its past — has ever harbored life. If the answer to that question is affirmative, then it leads to an important follow-up question: is that life related to or independent of life on Earth? It is possible that life originated on Earth and seeded Mars with life; it’s possible that life originated on Mars and then seeded Earth; it’s even possible that life predated both Earth and Mars, and early forms of it took hold on both planets.

But at this point in time, we have no overwhelming evidence that life ever existed on Mars at all. We have a few hints that could be indicators of past or present life there, but entirely inorganic processes could explain each and every one of those observed results.

As always, the only way we’ll find out the truth is by conducting more and better science with superior instruments and techniques. As NASA’s Perseverance rover moves ahead to collect a variety of soil samples, the next step will be returning them to Earth for laboratory analysis. If we succeed at that, we could know for certain, within the next decade, which of these five possibilities is most consistent with the truth about Mars.

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April 5, 2023

NASA’s Perseverance Rover May Already Have Evidence of Ancient Martian Life

A half-kilogram’s worth of samples gathered by NASA’s Perseverance rover for eventual return to Earth holds weighty implications for life on Mars

By Jonathan O'Callaghan

NASA’s Perseverance Mars rover took a selfie with several of the 10 sample tubes it deposited at a sample depot it is creating within an area of Jezero Crater nicknamed Three Forks.

NASA/JPL-Caltech/MSSS

If life ever existed on Mars, we may already have the answer at hand. In January NASA’s Perseverance rover deposited 10 tubes on the surface of Mars. Each contains a sample of Martian rock that was carefully selected for its potential to clarify chapters of the planet’s still-murky history. Those tubes “are capable of telling us whether Mars was habitable,” says Mitch Schulte, Perseverance’s program scientist at NASA Headquarters in Washington, D.C. “We see evidence of particular minerals that tell us there was water. Some of these minerals indicate there was organic material.”

But to know for sure, scientists need to bring these tubes back to Earth for closer study—an audacious endeavor known as Mars Sample Return (MSR), which is slated for the early 2030s via a follow-up robotic mission . These 10 tubes are only the opening course in a bigger awaiting feast, a backup cache in case Perseverance breaks down before it can fill and deliver the 33 additional tubes that it carries. These tubes will hold samples sourced from the area in and around Jezero Crater, the site of a four-billion-year-old river delta and the locale where the rover landed on February 18, 2021. Although many of the samples are yet to be gathered for a journey to Earth that remains years in the future, those already collected have whetted researchers’ appetite for their return home.

Scientists targeted Jezero for Perseverance because, on our planet, sprawling river systems like that found in the Martian crater build up enormous deposits of sediments. Washed in from a sizable swath of the surrounding landscape, these deposits contain various minerals that can be used to chart the Red Planet’s past geology. Also most anywhere water is found on Earth, life accompanies it. The same might hold true for Mars, meaning Jezero’s sediments could conceivably harbor biological remains. “We’re looking for signs of habitability—liquid water and the raw materials of life,” says Mark Sephton of Imperial College London, a member of the rover’s sampling team.

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A close-up of one of the Perseverance Mars rover’s 43 sample tubes, deposited for future retrieval on the surface of Mars. Credit: NASA/JPL-Caltech/MSSS

Perseverance collects most of its samples using a small drill, producing chalk-stick-sized specimens that each fit within cigarlike tubes measuring less than 15 centimeters long. Of the 43 sample tubes, 38 are slated for samples from the surface, with the remaining five being “witness tubes” to catch whiffs of Martian air and check for any contaminating gases that might vent from the rover. Collected in September 2021 , the rover’s first sample is thought to be igneous rock from an ancient lava flow. Studying this material should allow scientists to date the crater more precisely. Since then, the rover has filled nearly half of its remaining tubes as it journeys several kilometers further up the ancient river’s channels toward Jezero Crater’s rim.

As a contingency, 10 of the samples are duplicates, each paired with another sample taken from the same location. These are the tubes Perseverance dropped on the surface as backup for potential future retrieval. In December 2022, in one of the last decisions he’d make at the space agency before reentering the private sector, NASA’s then science chief Thomas Zurbuchen made the call to drop that cache at a location called Three Forks. The surface drop-off was completed at the end of January, around the same time Perseverance officially began the “extended” phase of its mission—and after the science team agreed that those 10 samples alone could answer the question of past habitability if needed. MSR’s optimal plan calls for the rover to carry its remaining tubes to a yet-to-be-built lander slated to touch down in Jezero’s vicinity around 2030. Once the lander has secured those samples, it will launch them on a rocket back to Earth .

“We want the ones on the rover to come back,” Zurbuchen says. “But even the ones on the surface check all the boxes.” That includes igneous rock to date the crater and sedimentary rock and clays that may contain biosignatures, perhaps even fossilized evidence of microbial life. “They’re already worth the $10-billion investment,” Zurbuchen says, citing the MSR program’s estimated total cost. Some of the most promising samples are from a location called Wildcat Ridge, a meter-wide rock that contains evidence of sulfates. “Those are the ones we’re most excited about in terms of potential biosignatures,” says Kathleen Benison of West Virginia University, who is part of Perseverance’s sampling team. “Sulfate minerals can grow from groundwater. On Earth, those kinds of waters tend to have a lot of microbial life,” which can be entombed and preserved in sulfate minerals.

Besides sulfates, life-seeking scientists are particularly eager to grab samples from mudstones—fine-grained sedimentary rocks that the Curiosity rover has seen in Gale Crater but that Perseverance has not yet spotted. “Microbe cells are tiny,” says Tanja Bosak of the Massachusetts Institute of Technology, who is also part of the sampling team. “The mineral grain size should be even finer to preserve the [fossil] shape instead of destroying it. If you roll a boulder over a person, you will smush that person into something unrecognizable. For a microbe, everything is a boulder—unless you’re talking about mudstones.” The team members are also keen to sample carbonates, similar to things like chalk and limestone on Earth, which could preserve biosignatures as well. “If there had been microbial life in the lake, [the carbonates] could have trapped microbial matter in it,” says Sanjeev Gupta of Imperial College London, who is one of the “long-term planners” who plot out the rover’s path. On March 30, Perseverance collected its first carbonate sample, from a rock named “Berea” thought to have formed from material washed into Jezero by the ancient river.

Taken on March 30, 2023, this image shows the rocky outcrop the Perseverance science team calls “Berea” after the NASA Mars rover extracted a carbonate rock core ( right ) and abraded a circular patch ( left ). Credit: NASA/JPL-Caltech

While Perseverance has been hard at work collecting samples on Mars, the return phase of the mission remains in flux. Originally, NASA had planned for a European-built “fetch” rover to land on Mars around 2030, collect the samples from Perseverance and return them to a capsule on the lander for launch. Once in orbit, the sample capsule would rendezvous with a European orbiter, which would ferry the samples back to Earth for a landing in 2033. These plans were complicated, however, by Russia’s invasion of Ukraine in 2022. In response to Russia’s aggression, European Space Agency (ESA) officials chose to step back from a partnership with the nation on another long-simmering Mars mission, the Rosalind Franklin ExoMars rover. Russia had been due to provide the rover’s nuclear power source, as well as the launch vehicle and landing platform. NASA has now agreed to supply such missing pieces and has sought funding to do so in its budgetary request to Congress last month. But this unanticipated assistance comes at the cost of the fetch rover. “We couldn’t do both,” Zurbuchen says. “We could not individually land the fetch rover and do ExoMars.”

The ExoMars mission, most everyone agrees, is eminently worth saving. The Rosalind Franklin rover will carry a drill that can augur two meters beneath the Martian surface, accessing a subterranean habitat for past and present life that is considerably less hostile than the surface. “Nobody has ever done that on Mars,” Zurbuchen says. “Our science community thinks it’s really important.”

Jorge Vago, ESA’s ExoMars project scientist in the Netherlands, was glad that NASA stepped in. To hit a target launch date of 2028, set forth by European member states in order to save the mission, “we need the American contributions,” Vago says. “It’s an amazing mission. If we find super interesting stuff that’s suggestive of a possible biological origin, I would expect we may want to have another sample return mission and bring back samples from the subsurface.”

NASA’s current MSR plan faces its own challenges. In a mid-March town hall hosted by NASA’s Science Mission Directorate, Jeff Gramling, MSR program director at NASA Headquarters, said that some aspects of the mission may need to be “descoped.” This would be a preventative measure to keep budgets under control. NASA’s annual request of nearly $1 billion for MSR is expected to grow in the next few years, raising fears that unchecked increases could force the space agency to siphon funds from unrelated missions. Descoping options include removing one of two “Marscopters” planned for MSR, which had been included to build on the wildly successful Ingenuity rotorcraft that is now approaching 50 flights on Mars . Among other tasks, MSR’s helicopters were added as a backup option for collecting the 10-tube sample cache at Three Forks. “The mission remains complex,” Gramling said during the town hall. “We’re working to our earliest possible launch date.”

Despite the overwhelmingly intricate logistics of seeking life on Mars, the scientific riches on offer have lost none of their luster. Perseverance’s returned samples will cumulatively be only about half a kilogram, but the weight of their implications is immeasurable. Will they reveal that a second genesis of life in the universe has unfolded on the surface of Mars? For that matter, will Rosalind Franklin, once it arrives, validate the long-held suspicion that Mars’s subsurface was—or still is—habitable, too? In our winding quest to determine if we are alone in the universe, the answer may be practically within our grasp, merely waiting for us to reach out to claim it. “We won’t know until we get the samples back,” Bosak says.

NASA just scored a badly needed win: The best potential evidence of alien life yet

• NASA's Perseverance rover has found potential evidence of ancient microbial life on Mars .
• Scientists must bring the rock to Earth for further study, but three key features make it promising.
• The discovery is a crucial win for NASA after a series of budget cuts and mission setbacks.

NASA has snagged a chunk of rock on Mars that could someday prove to be the first clear evidence of alien life .

To be clear, NASA is not declaring that it's discovered Martian life. Rather, its Perseverance rover has drilled a sample from a rock with attributes that could have come from ancient microbial activity, the agency announced Thursday.

To confirm their suspicions, scientists would need to bring the rock sample to Earth and study it in more detail.

"This is exactly the kind of sample that we wanted to find," Katie Stack Morgan, a lead scientist on the Perseverance mission , told Business Insider.

3 key features could point to alien life

The rock, nicknamed Cheyava Falls, has three critical features:

• First, white veins of calcium sulfate are clear evidence that water once ran through it.
• Second, the rock tested positive for organic compounds, which are the carbon-based building blocks of life, as we know it.
• Third, it's speckled with tiny "leopard spots" that point to chemical reactions that are associated with microbial life here on Earth.

However, both the organic material and the leopard spots could have come from non-biological processes. That's why scientists need to study the sample more closely on Earth to know for sure.

The rover has reached the limit of what it can learn about the rock.

"We're not saying there's life on Mars, but we're seeing something that is compelling as a potential biosignature," Stack Morgan said.

A biosignature is any feature that points to the presence of life .

Related stories

"This is a very significant discovery," she added.

It's a much-needed win for the space agency. In recent months, NASA has taken hit after hit from budget limitations and technical errors across missions.

NASA needs this win

Earlier this year, the agency's first attempt to return to the moon since 1972 failed. The NASA-funded Peregrine moon mission, by the company Astrobotic suffered a fuel leak shortly after launch, forcing it to return to Earth and burn up in the atmosphere. (The next attempt, a mission by the company Intuitive Machines , also funded by NASA, successfully landed on the moon.)

Then, new budgeting decisions came down. NASA's budget proposal for 2025 effectively defunds the Chandra X-ray Observatory , which is still a highly productive and functional mission.

And just last week, NASA officials announced they were scrapping the VIPER moon rover that the agency has already spent $450 million to build. NASA plans to disassemble it and reuse some of the parts for future moon missions.

Meanwhile, two astronauts have been stuck on the International Space Station for 51 days because the NASA-funded Boeing spaceship that carried them there is leaking helium and having thruster malfunctions.

Even Perseverance wasn't spared. In April, NASA announced it was canceling its $11 billion plan to send a follow-up mission, called Mars Sample Return, to collect the rover's tubes of Martian rock and carry them back to Earth. That was the plan that could've brought scientists the Cheyava Falls rock sample.

Instead, NASA is asking companies to step in and propose their own cheaper, faster versions of the mission.

The Cheyava Falls rock especially needs the extra studying.

"This rock is also one of the most complex rocks we've seen on the surface of Mars. There is a lot going on in this rock," Stack Morgan said.

I s it aliens? Check the CoLD scale

For now, this discovery is just a "step one" on the seven-step "confidence of life detection" (CoLD) scale.

The CoLD scale is a rough rating of scientific confidence in any potential alien-life discovery.

"We've taken us up to the start of that scale, and I think that's what the rover was sent to Mars to do," Stack Morgan said.

A possible biosignature can climb to higher levels of confidence as evidence builds. For example, if scientists can confirm that known non-biological processes didn't create the leopard spots, the Cheyava Falls rock might ascend to step two or three.

But they need to get the sample to Earth first. And NASA needs to figure out how to do that.

"We're hoping that our most recent sample can play into the conversation about whether this effort is worth it," Stack Morgan said. "And we believe that it is."

Watch: This asteroid dirt might explain the origins of life on Earth

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Exploring the Possibility of Living on Mars

May 11, 2017 James Miller News & Events , Space Missions 0

The Red Planet has garnered a lot of attention in recent times, as scientists obsess about the possibility of discovering evidence of life on Mars. Added to this, NASA and SpaceX plan to make humans visit to the planet within the next decade or so, but one of the biggest questions still remains unanswered concerning the long-term sustainability of human habituation on Mars.

Physical Challenges

• A low average surface temperature of -55 °C (-67 °F), and an atmosphere composed 95% of carbon dioxide lowers the possibility of creating sustainable life on the Mars.

• Having a gravity a mere 38% that of the Earth creates obvious mobility challenges for humans, as well as wreaking havoc on our cells, bones, and muscles, ultimately making a healthy return back to Earth unlikely.

• The atmosphere of Mars is around just 1% that of the Earth’s, meaning it offers no protection from the harmful radiation coming from the Sun.

Journey and Landing

Lets now explore the amount of time astronauts would take to reach Mars, and the possible ways scientists have devised for landing on the planet’s surface upon arrival. While the distance between the Earth and Mars ranges between 33.9 million miles (54.6m km) and 250 million miles (401m km), at their shortest point (perihelion) the journey to Mars may take just 260 days to complete. Considering this relatively short travel time, scientists have come up and implemented quite a few possible landing ideas over the years, although with the advent of technology scientists from NASA are currently exploring the possibility of a lander deep diving into the planet’s thick surface atmosphere before skirting close to its surface using jets.

Creating a Habitat

Studies on the subject of human habitation on Mars have concluded that the most suitable habitats on the planet need to be self-sustaining with the capability of supporting life for extended periods without any support from Earth. There is still a lot of work that needs to be done in this direction, but NASA has already selected six American companies to help develop full-sized prototypes for these ground habitats. As Richard McGuire Davis, co-leader of NASA’s Mars Human Landing Sites Study, explains:

“The International Space Station has really taught us a tremendous amount of what is needed in a deep space habitat. We’ll need things like environmental control and life support systems (ECLSS), power systems, docking ports, [and] air locks so that crew can perform space walks to repair things that break or to add new capabilities.”

Plant Growth

The first goal of colonization is learning how to live on the planet as survival is the biggest priority. Having learned the survival basics, there is a world of things to explore in time such as the possibility of farming, how to utilize water from the ice-capped poles of Mars , managing plant growth and so much more.

Having sufficient food and medicine supplies stocked on Mars is a good idea, but the planet’s thin atmosphere and reduced sunlight will make it a challenge for anything to grow. There are a number of suggestions to cope with this significant challenge, including the use of artificial leaves made of silicone rubber that can absorb some of the sunlight and turn it into enough power to initiate the chemical reactions necessary for creating “pharmaceuticals, agrochemcials or solar fuels.”

While the Martian soil contains minerals, it has none of the organics biological materials that plants need to grow, though, and in the distant future, the planet’s soil inside green houses will need to be detoxified, while water from the Martian ice-caps will need to be utilized in order to support intensive farming activities.

With rapid advancements in science and technology, scientists and space organizations are rapidly gaining valuable insights into the possibility of life in the universe, with the planet Mars providing a unique case study. It will be interesting to see how things move forwards over the next few years, especially with Mars having been a source of great fascination and inspiration for the human imagination over our entire history.

• Planets and Moons

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Mars Sample Return: Issues and Recommendations (1997)

Chapter: 2 the possibility of extant life on mars, 2 the possibility of extant life on mars.

Although current evidence suggests that the surface of Mars is inimical to life as we know it, there remain plausible scenarios for extant microbial life on Mars—for instance, in possible hydrothermal oases or in subsurface regions.

THE CONTEMPORARY MARTIAN ENVIRONMENT

The surface of Mars today is generally inhospitable to life as we know it. It is cold, dry, and chemically oxidizing and is exposed to an intense flux of solar ultraviolet radiation.

Temperature is of interest, not only because of its controlling influence on metabolic rates but also because of its influence on the stability of liquid water. Although the peak daytime surface temperature near the equator can rise above the freezing point of water during much or all of the year, the average surface temperature is about -55°C, well below the freezing point of water.

Liquid water is essential for life as we know it, as all known terrestrial life is based on aqueous chemistry. Given our current state of knowledge in chemistry and biology, it is hard to imagine the existence of life independent of liquid water.

Water is abundant on Mars but not in liquid form (e.g., Jakosky and Haberle, 1992). Water vapor and ice crystals are present in the atmosphere. In fact, because of the cold temperature of the atmosphere, water is often saturated there or near the surface. Water-ice almost certainly is present in the soil at high latitudes, where the subsurface temperatures are cold enough that atmospheric water vapor can diffuse from the atmosphere into the surface and condense as ice. Ice is present at the surface in the polar regions as well. During the half-year-long north-polar summer, the water-ice residual polar cap heats up enough to allow water to sublime into the atmosphere and be distributed globally. The polar surface temperatures are too low, however, for the ice to melt.

It is possible that liquid water may exist transiently on or near the surface in isolated pockets, although such occurrences probably are very rare. The presence

of salts of the right composition and in sufficient quantity can lower the freezing point enough to allow a liquid solution to exist, although such a liquid is unstable with respect to evaporation (Clark and Van Hart, 1981). Alternatively, ice crystals trapped in closed pores in rocks or regolith grains could melt under certain circumstances, and the resulting liquid water could be prevented from evaporating by virtue of being enclosed.

Analytical experiments carried aboard the Viking landers indicated that the surface environment of Mars is highly oxidizing, although the exact nature of the oxidants was not determined (Hunten, 1979). It is possible that the martian soil contains oxidants, such as hydrogen peroxide, which are postulated to form photochemically from atmospheric water vapor and to diffuse readily into the soil. If present, such oxidants would react with, and destroy, organic molecules or biota and could be effective in sterilizing the surface environment. Their presence may be responsible for the absence of organic molecules in the soil.

The Viking lander experiments found no organic substances in the soil despite the fact that organic molecules are being added continually from meteorite impacts (Biemann et al., 1977).

The atmosphere is relatively thin, averaging about 6 millibar pressure, and consists primarily of carbon dioxide. Owing to the low concentration of atmospheric ozone, ultraviolet light from the sun can reach the surface of Mars almost unattenuated. Winter-hemisphere atmospheric ozone can absorb some of the ultraviolet, but only during a fraction of the year and only over a fraction of the planet. The attenuation is much less than that due to the ozone layer on Earth. Thus, throughout the martian year the entire surface of the planet is subject to an intense flux of ultraviolet radiation.

THE ANCIENT MARTIAN ENVIRONMENT

The surface environment of Mars may not always have been so hostile to life. Early in the planet's history, the average temperature almost certainly was warmer and the atmosphere more dense, and liquid water may have existed at the surface. Evidence for the presence of surface water on early Mars comes from interpretation of the geomorphology of the planet's surface. A substantial fraction of the surface of Mars is older than about 3.5 billion years, based on the number of impact craters, which provide a window into the planet's early history.

Two aspects of these older surfaces suggest that the climate prior to about 3.5 billion years ago was different from the present climate (Squyres and Kasting, 1994). First, impact craters smaller than about 15 kilometers in diameter have been obliterated on these older surfaces, and impact craters larger than this have undergone substantial degradation, whereas younger impact craters have not been altered significantly. This suggests that erosion rates were up to 1,000 times larger early in martian history. The style of erosion that is seen on some of the remaining larger impact craters is indicative of water runoff, and water erosion is

considered to be responsible for removing the smaller craters. Second, many of the same older surfaces contain networks of valleys that form dendritic patterns similar to terrestrial water-carved stream channels. There is continuing debate as to exactly how these valleys were formed—the process may have involved runoff of precipitation, seepage of subsurface water in a process termed "sapping," or erosion by water-rich debris flows. Independent of the exact process, their formation must have involved the presence of liquid water at or very near the surface during these earlier epochs (Carr, 1996).

Thus, geological evidence suggests that the martian climate prior to about 3.5 billion years ago was somehow warmer than the present climate and that liquid water flowed on the surface in a way that is not observed today. Unfortunately, the observations do not allow a unique determination of what the temperature, atmospheric pressure, or partitioning of liquid water between the subsurface, surface, and atmosphere were at that time. Evidence from measurements of martian stable isotopes suggests that a large fraction of the volatiles from early Mars may have been lost to space, causing the surface environment to become cooler and drier and to evolve into the state observed today (Jakosky et al., 1994).

COULD LIFE HAVE ARISEN ON MARS?

Life on Earth appeared sometime prior to 3.5 billion years ago, although the details of its origin are unknown (e.g., Chyba and McDonald, 1995). The origin of life is believed to require a source of organic molecules, a source of energy that can drive disequilibrium processes, and access to the biogenic elements (such as carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus) (Chang, 1988). The source of organic molecules could be external—for example, organic molecules formed in interplanetary space and supplied to Earth along with meteoritic dust and debris that accreted onto Earth, or terrestrial, formed by chemical reactions in Earth's environment. Transient evaporating ponds, hydrothermal vents where water circulates beneath the surface near volcanic intrusions, and the surfaces of clay minerals that could provide stability and order to long chains of molecules have all been postulated as candidate environments where prebiotic chemistry may have undergone a transition leading to self-replicating entities.

Significantly, molecular phylogeny techniques that allow determination of the genetic distances between modern-day terrestrial species (Woese, 1987) suggest that their most recent common ancestor may have been hyperthermophilic, existing in water heated by near-surface volcanic magma. This indicates either that life first arose in a hydrothermal (hot-spring-like) environment or that it passed through some hydrothermal bottleneck event, such as heating of the early oceans by an energetic asteroid impact, during which nonhyperthermophilic organisms were exterminated.

Hot-spring environments may have been widespread on early Mars (Brakenridge et al., 1985). Hot springs or hydrothermal systems require water in

the crust and substantial sources of heat. Local heating of the crust can result from meteorite impacts. Such impacts were a common occurrence during the tail end of the heavy bombardment, as recorded in the impact craters on the oldest surfaces; thus local thermal anomalies that could have driven hydrothermal systems were probably common at the time. Isotopic evidence from martian meteorites indicates that the planet melted globally and differentiated shortly after accretion. The hot initial conditions imply extensive early volcanism. The rate of volcanic activity probably declined with time, but numerous volcanic landforms indicate that Mars has remained volcanically active throughout its history. Clearly, there has been sufficient heat to drive hydrothermal circulation throughout the history of the planet, although such activity was more common early in its history.

Geological evidence also suggests that abundant water has been present in the crust (Carr, 1996). The evidence is derived from the form of the valley networks that involved liquid water, as discussed above; catastrophic flood channels that indicate the presence of water reservoirs in the crust; morphologies such as rampart crater ejecta and lobate debris aprons that might be indicative of near-surface ice; and, of course, the polar caps, which contain substantial quantities of water. Given the extensive evidence for both heat sources and accessible water, it is likely that hydrothermal systems have been present throughout martian history.

The climate on early Mars may have been similar to the climate on Earth at that time. Although martian erosion rates undoubtedly were substantially lower than terrestrial erosion rates, suggesting less widespread water, liquid water certainly was present on both planets. Both planets probably had a mildly reducing atmosphere, containing substantial quantities of carbon dioxide. Given that life arose on Earth, it seems possible and even plausible that life could have arisen on Mars under similar conditions and at roughly the same time. If such were the case, a significant community of microorganisms may have existed on early Mars (McKay et al., 1992a,b; Boston et al., 1992).

Interestingly, an alternative source for life on Mars may have been Earth itself. Asteroid impacts are capable of ejecting rocky material from planets into space (see Chapter 3 ). Once in space, close encounters with their planet of origin would alter the orbits of such material. The orbits of material ejected from Mars could evolve to the point that they would cross the orbit of Earth; similarly, ejecta from Earth could evolve to the point that their orbits would cross the orbit of Mars (Melosh, 1988; Gladman et al., 1996). At that point, collisions could occur, providing a mechanism for transferring mass from one planet to the other. Meteorites have been discovered on Earth that are identified as having come from Mars, indicating that this process actually does occur. A martian origin for these meteorites is indicated by their young age, by the presence of oxygen isotopes that rule out an origin on Earth or the moon, and by gases trapped within them that are identical in composition to the martian atmosphere and distinct from any

other known source of gas in the solar system (Bogard and Johnson, 1993; McSween, 1994). Some of the material ejected by an impact is not heated or shocked substantially, and bacteria or bacterial spores may be able to survive the ejection event. If organisms or spores could survive within a rock during interplanetary transit and find a satisfactory environment on a new planet, they could possibly survive and multiply. This would allow living organisms on one planet to be transferred to another. Indeed, one can ask the following questions: On which planet did life originate? Could life have originated on Mars and been transferred to Earth or vice versa?

IF LIFE DID ARISE, COULD IT SURVIVE UP TO THE PRESENT TIME?

If life forms ever existed on Mars, either by having been formed in an independent origin or by having been transferred there from Earth, it is possible that they have continued to exist up to the present time. Such life forms could survive in occasional localized ecological niches. Such niches could be liquid water or hot springs associated with extrusive and intrusive volcanism or liquid water buried deep beneath the surface where it is stable. It is important to note, however, that biological material may not stay confined in such locations; organisms conceivably might produce dormant propagules (spores) that could be dispersed more widely.

Although volcanism has been declining in intensity throughout the latter half of martian history, it has occurred up to recent times and possibly to the present (Greeley and Schneid, 1991). Certainly, volcanism has occurred in the most recent recognizable geological epoch. This epoch, known as the late Amazonian, occupies approximately the last half billion years of martian history. Evidence for recent volcanism also comes from the martian meteorites. Many of these are basaltic rocks formed by volcanism more recently than 200 million years ago, and so it seems unlikely that volcanic activity just recently ceased. The abundance of water in the martian crust suggests that recent surface or near-surface volcanism might involve associated hot springs or near-surface hydrothermal systems where life could thrive. In addition, life could exist deep in the crust, where liquid water could occur. The geothermal temperature gradient is such that Mars is likely to have liquid water near the equator at depths as shallow as only about 2 kilometers (Carr, 1996). The presence of water is suggested by large flood channels that appear to have been caused by the occasional sudden release of large quantities of water from deep below the surface. The recent discovery of terrestrial organisms living deep within the Columbia River basalts in the Pacific Northwest (Stevens and McKinley, 1995), and elsewhere on Earth as deep as 3 kilometers below the surface, bolsters the possibility of organisms living under similar conditions on Mars. These organisms survive by metabolizing hydrogen that has been produced by chemical interactions between pore water and the ba-

salt; they are thought to be completely independent of any input of chemical energy from the surface, and to survive completely isolated from it. Presumably, these organisms did not originate in the basalt but migrated there from elsewhere. Similar migration to the deep subsurface could have occurred on Mars as surface temperatures declined from early higher values to their present cold level.

Did results from the Viking mission in the late 1970s not suggest that Mars was probably devoid of life? That was the accepted interpretation at the time, based on the results of three experiments that tested for biological activity and the absence of organic molecules in the surface materials (Klein, 1979). However, this conclusion may be open to some debate based on recent advances in our understanding of biology. The Viking experiments were able to test for only a couple of the possible mechanisms by which putative martian organisms might obtain energy; these involved the utilization of either carbon dioxide or extant organic molecules as a source of carbon in the production of organic molecules. Putative martian biota might employ other mechanisms to obtain energy and might do so under physical conditions quite different from those of the Viking biology experiments. Martian life also might reside in the interior of rocks (which were not sampled by Viking), where liquid water might occur. Finally, if life exists only in isolated oases where liquid water exists, such as recent volcanic vents or fumaroles, the Viking experiments might have been the right ones but carried out at the wrong location.

Furthermore, recent analyses of one of the martian meteorites, ALH84001, suggest that it contains possible indicators of ancient biological activity (McKay et al., 1996). This meteorite crystallized 4.5 billion years ago and contains abundant carbonate veins that appear to have been deposited in water through aqueous or hydrothermal activity. The possible indicators include carbonate mineral zonation and the presence of mineral grains similar to those found in terrestrial mineral deposits of biological origin, the presence of polycyclic aromatic hydrocarbons (PAHs) that may be remnants of decayed organic matter (although PAHs can also be formed by inorganic processes), and the presence of features that some researchers have interpreted as bacteria-like fossil biota. However, despite the occurrence of several intriguing indicators, the biological origin of these features has not yet been demonstrated with a high degree of certainty.

CONCLUSIONS

In summary, the surface of Mars is inhospitable to life as we know it, although there may be localized environments where life could exist. Conditions on Mars may have been conducive to the formation of life, either during an earlier epoch when the climate was likely more clement or in hydrothermal systems and hot springs that may have existed on Mars throughout geological time. Therefore, it is possible that life arose on Mars. It is also possible that living organisms from Earth could have been delivered to Mars by impact transfer, and, if so, such

organisms might have chanced upon the occasional oasis in which they could survive and multiply. If life arose on Mars or was delivered to Mars from Earth, it is possible that it has survived in localized environments that may be more hospitable than the general surface. Thus, there are plausible scenarios in which a sample returned from Mars could contain living organisms, either active or dormant.

The Space Studies Board of the National Research Council (NRC) serves as the primary adviser to the National Aeronautics and Space Administration (NASA) on planetary protection policy, the purpose of which is to preserve conditions for future biological and organic exploration of planets and other solar system objects and to protect Earth and its biosphere from potential extraterrestrial sources of contamination. In October 1995 the NRC received a letter from NASA requesting that the Space Studies Board examine and provide advice on planetary protection issues related to possible sample-return missions to near-Earth solar system bodies.

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Essay on Life on Mars for Students and Children

500 words essay on life on mars.

Mars is the fourth planet from the sun in our solar system. Also, it is the second smallest planet in our solar system. The possibility of life on mars has aroused the interest of scientists for many years. A major reason for this interest is due to the similarity and proximity of the planet to Earth. Mars certainly gives some indications of the possibility of life.

Possibilities of Life on Mars

In the past, Mars used to look quite similar to Earth. Billions of years ago, there were certainly similarities between Mars and Earth. Furthermore, scientists believe that Mars once had a huge ocean. This ocean, experts believe, covered more of the planet’s surface than Earth’s own oceans do so currently.

Moreover, Mars was much warmer in the past that it is currently. Most noteworthy, warm temperature and water are two major requirements for life to exist. So, there is a high probability that previously there was life on Mars.

Life on Earth can exist in the harshest of circumstances. Furthermore, life exists in the most extreme places on Earth. Moreover, life on Earth is available in the extremely hot and dry deserts. Also, life exists in the extremely cold Antarctica continent. Most noteworthy, this resilience of life gives plenty of hope about life on Mars.

There are some ingredients for life that already exist on Mars. Bio signatures refer to current and past life markers. Furthermore, scientists are scouring the surface for them. Moreover, there has been an emergence of a few promising leads. One notable example is the presence of methane in Mars’s atmosphere. Most noteworthy, scientists have no idea where the methane is coming from. Therefore, a possibility arises that methane presence is due to microbes existing deep below the planet’s surface.

One important point to note is that no scratching of Mars’s surface has taken place. Furthermore, a couple of inches of scratching has taken place until now. Scientists have undertaken analysis of small pinches of soil. There may also have been a failure to detect signs of life due to the use of faulty techniques. Most noteworthy, there may be “refugee life” deep below the planet’s surface.

Get the huge list of more than 500 Essay Topics and Ideas

Challenges to Life on Mars

First of all, almost all plants and animals cannot survive the conditions on the surface of Mars. This is due to the extremely harsh conditions on the surface of Mars.

Another major problem is the gravity of Mars. Most noteworthy, the gravity on Mars is 38% to that of Earth. Furthermore, low gravity can cause health problems like muscle loss and bone demineralization.

The climate of Mars poses another significant problem. The temperature at Mars is much colder than Earth. Most noteworthy, the mean surface temperatures of Mars range between −87 and −5 °C. Also, the coldest temperature on Earth has been −89.2 °C in Antarctica.

Mars suffers from a great scarcity of water. Most noteworthy, water discovered on Mars is less than that on Earth’s driest desert.

Other problems include the high penetration of harmful solar radiation due to the lack of ozone layer. Furthermore, global dust storms are common throughout Mars. Also, the soil of Mars is toxic due to the high concentration of chlorine.

To sum it up, life on Mars is a topic that has generated a lot of curiosity among scientists and experts. Furthermore, establishing life on Mars involves a lot of challenges. However, the hope and ambition for this purpose are well alive and present. Most noteworthy, humanity must make serious efforts for establishing life on Mars.

FAQs on Life on Mars

Q1 State any one possibility of life on Mars?

A1 One possibility of life on Mars is the resilience of life. Most noteworthy, life exists in the most extreme places on Earth.

Q2 State anyone challenge to life on Mars?

A2 One challenge to life on Mars is a great scarcity of water.

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Life On Mars

Jul 22, 2014

690 likes | 2.63k Views

Life On Mars. Mars is the only planet in our solar system to have frozen carbon dioxide snow it happens all year round in the north end. pictures from the mars curiosity shows landscapes made by bodies of water, rain and ancient rivers with the force of 10,000 Mississippi rivers.

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Presentation Transcript

Life On Mars • Mars is the only planet in our solar system to have frozen carbon dioxide snow it happens all year roundin the north end. • pictures from the mars curiosity shows landscapes made by bodies of water, rain and ancient rivers with the force of 10,000 Mississippi rivers. • the ALH84001 meteorite was catapulted from mars 15 million years ago and landed in Antarctica where nasa did studies and found microscopic worm like fossils and possibly evidence of other life on mars. • Recent discoveries on mars include structures similar to the ones on earth such as pyramid like structures and also what looks like the bottom half of the sphinx.

Crop Circles • Crop circles are a geometric patterns that appear in crop fields. All the crops that are in the field aren't cut but usually laid flat and most often swirled into an attractive floor pattern. • The size of a crop circle can range anywhere from a few feet across to several hundred feet in diameter. • Crop circles have been appearing in grain fields over the last few decades. • They suddenly appear over night. • Scientists have said that crop circles must have been created by intelligent aliens being from elsewhere. • There has almost been 200 cases of crop circles reported prior to 1970.

Extraterrestrials In the Nasa Organization they have found that there is tiny aliens bugs different kinds of bugs that hasn’t been found on the earth before. They have different kinds of Laboratory tests and they had different kinds of organisms inside of the meteorite that has hit planet earth. The Nakhla Meteorite that fell into Egypt nearly 95 years ago may have clues on extraterrestrial life. In 2001 a group of researchers found what could be the first proof of life beyond our planet in the form of clumps of extraterrestrial bacteria in the Earths upper atmosphere.

References • http://www.guardian.co.uk/science/2012/may/21/public-react-seti-evidence-alien-life • http://www.cbsnews.com/8301-501465_162-20039658-501465.html • http://www.thelivingmoon.com/46_mike_singh/03files/Sentient_Life_01.html

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‘Merci, Paris!’ Our Olympic reporter pens a love letter to the City of Light.

• Deep Read ( 5 Min. )
• By Ira Porter Staff writer

August 8, 2024 | Paris

Covering the 2024 Paris Olympics has been the best assignment of my career. Athletes train for years to get here. They know nothing is guaranteed. I tried to bring the same energy and dedication as the Monitor’s correspondent.

This was my first visit to Paris, but you better believe I’ll be back. My wife, son, and daughter came with me, so we got a chance to create some family moments with the scenic Parisian landmarks as our background.

Why We Wrote This

Our reporter at the 2024 Olympics stayed upright through some hard-charging days, but also fell hard for host city Paris. We’ll let him tell you all about it – in this first-person report and on a podcast episode that we’ve embedded.

I walked all over this city, until my feet hurt. I tried to absorb as much as I could, from gazing at the fading salmon-colored sun I could see in the Arc de Triomphe to dancing outside Paris City Hall. I absolutely ate excellent crepes and baguettes, but also delicious doro wot from an Ethiopian place in my neighborhood. The Whispers released a song in 1972 that sums up how I feel about the City of Light. It goes, “I said I only meant just to wet my feet / But you pulled me in where all the waters of love run deep.”

I love you, Paris. I meant to take the job that was entrusted to me seriously. But I fell hard for you. Merci !

Covering the 2024 Paris Olympics has been the best assignment of my career. I haven’t run one race, dribbled a single ball, shot an arrow, or soared over any hurdles like the thousands of athletes who competed here in Paris. But like them, I stayed in the moment and tried to grab slices of the world they created through competition at venues throughout this beautiful city.

Athletes  train for years to get here . They maintain strict diets, keep odd hours, spend countless amounts of money training, and as we have seen in these games, sometimes endure painful injuries to perform for the world. They know nothing is guaranteed. I tried to bring the same energy and dedication as the Monitor’s correspondent.

On the Run at the Games

When a sports-loving writer gets a shot at covering an Olympic Games, the story becomes one of joyful immersion and inspired output. Ira Porter joins host Clay Collins for this episode about reporting from the Paris Games and finding the human stories that matter most in that sea of competition and aspiration, heartbreak and triumph.

I crisscrossed the Seine River by train and foot every day, taking notes as fast as I could about the atmosphere in the Bercy Arena as Team USA women’s gymnastics recaptured gold in the team all-around competition. And like audience members, I marveled in surprise when the men’s team broke a 16-year drought and won bronze.

It got so hot at Eiffel Tower Stadium while journalists jotted down notes and took pictures from the press box as Team USA’s beach volleyball team beat France in straight sets that a stadium volunteer sprayed us down with water. That experience, I wasn’t fond of. After the women won, I stayed to watch a men’s game between Chile and the Netherlands, when the sky opened up and sent me running toward the press center to type up my notes.

Just like the weather, my experience in Paris has been unpredictable. There were ridiculously loud arenas, like La Defense, where swimmers literally soaked in the chants of their countrymen to win gold, silver, and bronze . I looked on with great empathy as unsuccessful athletes cried after falling short of their goals. The opening ceremony was a soaker, but worth more than three hours in the rain to watch brilliant French performers and athletes on ships sail by , waving hands and flags at onlookers.

I saw indelible moments get sketched into history books at Stade de France, as only racing feet can do, while the world gaped in awe at the speed of contests decided in seconds . Witnessing these feats filled my imagination with themes for stories to write. Perseverance, resilience, and bravery are just some of the words that come to mind. Or trendsetter, like Simone Biles. The best gymnast in the world couldn’t complete a majority of events in the Tokyo Olympics in 2021, partly because of mental health issues, which she has spoken openly about both before and at these games. Even here, she shied away from the village where athletes are housed, because the pressure gave her anxiety. By putting herself first, returning to her sport, and dominating, she set the new standard that all athletes can follow.

Thursday night, I watched one of the best games that I have ever witnessed in person as Team USA men’s basketball survived a scare from Serbia. The U.S. trailed all game by as much as 17 points. With less than 5 minutes left, they stormed back, intensified their defense, and fed the cheering crowd, who in return propelled them to victory. Team USA will next face France in the finals. This win is the embodiment of what the Olympics are. One shot to prove yourself and leave it all on the court. I bet the more than 16,000 fans in the Bercy Arena will remember this forever. I will.

I can’t play sports as well as any of the 10,500 athletes who competed in Paris over these two weeks. But I sought to bring a similar rigor and commitment to long hours when presenting this experience to Monitor readers. When readers look back at the first post-pandemic Olympics, I hope they notice the variety that we thought about in our presentation. I hope they can see the trends that we picked up on, like this being the first Olympics where there was gender parity , with about equal numbers of men and women athletes and equal medals up for grabs.

My one wish is that I could have covered more. I wish I could have somehow visited all 35 venues where Olympic competitions were held – with backpack, water bottle, computer, digital recorder, and notebook in tow – and meticulously played back for readers every drop of sweat, fist pump, or cheer.

This was my first visit to Paris, but you better believe I’ll be back. My wife, son, and daughter came with me, so we got a chance to create some family moments with the scenic Parisian landmarks as our background. It was the perfect blend of building a life and a career for me, and hopefully teaching my children to allow their lives to expand by having courage and taking chances. This was the first trip out of the country for my children, who anxiously wondered what tasty food would be served on our flight. In Paris, I have smiled at them trying desperately to grasp at the language and greet strangers on the subway, at restaurants, and in playgrounds.

I walked all over this city, until my feet hurt. I tried to absorb as much as I could, from gazing at the fading salmon-colored sun I could see in the Arc de Triomphe to dancing outside Paris City Hall. I absolutely ate excellent crepes and baguettes, but also delicious doro wot from an Ethiopian place in my neighborhood, a great Vietnamese bahn mi, and incredible Lebanese food. The R&B group The Whispers released a song in 1972 that sums up how I feel about the City of Light. It goes: “I said I only meant just to wet my feet / But you pulled me in where all the waters of love run deep.”

I love you, Paris. I only meant to come here, work, and put my stamp on these games – to take the job that was entrusted to me seriously. But I fell hard for you. Merci !

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NASA Made a World-Shaking Discovery: Compelling Evidence of Past Life on Mars

In its ancient past, Mars likely contained many of the necessarily ingredients for microbial life to flourish on its surface.

Now, a new discovery by NASA’s Perseverance rover shows a trifecta of compelling evidence—including the presence of water, organic compounds, and a chemical energy source—all on one rock located in the Jezero Crater.

Although this is the best clue yet that microbial life existed on Mars, there are still other explanations that could explain this geologic display without the existence of microbes.

“ Is there life on Mars ” is a question that has vexed astrobiologists and David Bowie alike. While the latter imagined some macabre collection of arachnids on the Red Planet, NASA scientists are fixated on finding evidence that microbial life once flourished on the fourth rock from the Sun . So fixated, in fact, that the space agency has spent more than $5 billion getting two immensely complicated robotic rovers—Curiosity and Perseverance—onto the Martian surface with this specific microbial mission in mind.

Now, one of those rovers might’ve discovered one of the most compelling pieces of evidence for Martian microbial life . Located on an arrowhead-shaped, three-foot-long rock nicknamed “Cheyava Falls” in the Jezero Crater (the 28-mile-wide crater that Perseverance has called home for the past three years), this “piece of evidence” is actually a trifecta of data points that suggest the presence of past microbial life. The rock in question features two vertical veins of calcium sulfate that likely formed from past water, and these stripes both flank a red band of rock filled with “leopard spots.”

NASA has discovered evidence of past water on Mars before, but it’s this narrow band of rock that brings new meaning to this discovery. Using its SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals) and PIXL (Planetary Instrument for X-Ray Lithochemistry) instruments, Perseverance determined the existence of organic compounds within the rock. Oh, and those “leopard spots?” Those likely indicate chemical reactions that could’ve supplied energy to ancient microbial Martians.

While each of these discoveries—the presence of water , organic compounds, and chemical reactions—would be notable even if discovered separately, NASA has never seen all three in one location, meaning the geological chemistry of Cheyava Falls is possibly our best clue yet that Mars once hosted life.

“Cheyava Falls is the most puzzling, complex, and potentially important rock yet investigated by Perseverance ,” Caltech’s Ken Farley, Perseverance project scientist, said in a NASA press statement . “We have our first compelling detection of organic material, distinctive colorful spots indicative of chemical reactions that microbial life could use as an energy source, and clear evidence that water—necessary for life—once passed through the rock.”

While this site is particularly exciting, it’s far from the first Martian discovery to cause considerable microbial hype. Just earlier this year, scientists studying a 2017 soil analysis from Curiosity’s ongoing mission in Gale Crater discovered an abundance of manganese in the soil—something that usually requires the presence of oxygen and (you guessed it) microbes.

But all of these discoveries come with more than a few caveats. In Curiosity’s case, too little is known about the Mars’ oxidation process to be certain that microbes existed in Gale Crater, and this new discovery also isn’t immune from scientific scrutiny. One big head scratcher is the presence of millimeter-sized olivine crystals —a mineral that forms from magma. This may possibility explain how past volcanic activity could produce this geologic phenomena without relying on the presence of microbes at all.

“We have zapped that rock with lasers and X-rays and imaged it literally day and night from just about every angle imaginable,” Farley said in the press statement. “Scientifically, Perseverance has nothing more to give. To fully understand what really happened in that Martian river valley at Jezero Crater billions of years ago, we’d want to bring the Cheyava Falls sample back to Earth, so it can be studied with the powerful instruments available in laboratories.”

The “six-wheeled geologist” (as NASA calls it) doesn’t contain an onboard lab like its sister rover, Curiosity. But that’s actually a feature—not a flaw. NASA originally designed Perseverance to also be a sample retrieval mission, meaning that the space agency would send an additional spacecraft to retrieve samples from Perseverance and bring them back to Earth for further study.

However, with the costs of such a mission edging into the $11 billion range , bringing back samples of this Martian geologic wonder is in now question—as is the possibility of definitively understanding if there was once microbial life on Mars.

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