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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.

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Is there life on Mars? A NASA scientist explains in new video

Could life have once existed on Mars, or could it still prosper there to this day?

The search for life beyond Earth is a core motivation of many missions to explore the Red Planet and in this new video, a NASA scientist takes a close look at the question driving it all: Is there life on Mars?

NASA has a number of missions in operation at the surface of Mars that are intensely engaged in the search for traces of life. Primary among these missions are the rovers Curiosity , which landed on Mars in 2012, and Perseverance which set down on the Martian surface in 2021. The latter of these has been collecting cores from rocks from the Jezero Crater where minuscule traces of life may have been trapped.

“We're just now getting instruments onto the Martian surface that can help us understand these potentially habitable places and we can ask deeper questions about the potential for habitability in those rock cores," Heather Graham, an astrobiologist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in the 1-minute video released on Dec. 28 . "We've been looking for life on Mars for a long time."

Related: How Mars microbes could survive in the salty puddles of the Red Planet

NASA scientist Heather Graham is an organic geochemist and research associate based at the agency's Goddard Space Flight Center in Greenbelt, Maryland who studies the connections beween biotic and abiotic systems. Her research focuses on "agnostic biosignatures," which NASA describes as evidence of living systems that may not share commonalities with life on Earth.

Graham's research has focused on the development of tools and techniques that can help us identify evidence of living systems that may have biochemistry different than life on Earth, also known as "agnostic biosignatures." 

As they investigate Mars and aim to study other solar system planets for traces of life, scientists need detection methods that suppose a common heritage with life on Earth. These methods could also help scientists understand life deep within the Earth where life could be very different than that at the surface of the planet as a result of following different evolutionary lines for billions of years.

"And while NASA hasn't found any evidence of life now, we've found lots of evidence that Mars could have supported life in the past,” Graham explained. "There are lots of pieces of evidence that say there was once a huge ocean on Mars and an atmosphere that could have supported life."

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One of the most important lines of evidence that suggest Mars could have once supported life is the fact that the now dry and arid planet once harbored an abundance of water, a key ingredient for life.

The fact that the 45-kilometer-wide (28-mile-wide) Jezero Crater was once flooded with water and was home to an ancient river delta is the reason NASA chose it as the landing area for the Perseverance rover. 

Around 4 billion years ago the river channels in Jezero spilled over the crater walls creating a lake, also filling it with clay minerals from the surrounding area. If microbial life existed in Jezero during these wetter Martian, times signs of this life could remain in the lakebed or shoreline sediments. Thus, the signs of this past life could exist in samples of Mars rock and soil collected by Perseverance. 

— Incredibly weird microbes found deep underground could change search for life on Mars

— Could there be life on Mars today?

— How stratospheric life is teaching us about the possibility of extreme life on other worlds  

On Earth , our magnetic field stops harmful radiation from stripping away the atmosphere and protects life on the planet’s surface. Mars is believed to have lost its water when it lost its magnetic field around 4 billion years ago. Without an atmosphere, there was nothing to prevent Mars’ water from evaporating and then being lost to space. This radiation also made the existence of life at the surface of Mars unfeasible.

Yet, there is a chance that liquid water could still exist beneath the surface of the planet and thus Graham thinks that if life still exists on Mars it would also be beneath the planet's outer layers. The advantage of a subsurface dwelling would be layers of rock and soil providing protection from harmful solar radiation once delivered by the Red Planet’s magnetic field. 

"There are places that are potentially habitable, like the deep subsurface. There are places underground that could have fluids in them or organisms could live, and they’d be protected from the radiation that’s so harmful on the surface," Graham explained. "So is there life on Mars? Not that we've found yet, but there's still a lot of Mars left to explore."

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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].

Robert Lea is a science journalist in the U.K. whose articles have been published in Physics World, New Scientist, Astronomy Magazine, All About Space, Newsweek and ZME Science. He also writes about science communication for Elsevier and the European Journal of Physics. Rob holds a bachelor of science degree in physics and astronomy from the U.K.’s Open University. Follow him on Twitter @sciencef1rst.

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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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Life on mars

My creativity. Is Mars really have capacity to sustain human life in future?? Read less

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• 1. LIFE ON MARS EXPLORATION OF LIFE
• 2. Why would we want to live on other worlds?  Population growth  Survive asteroid impacts  Develop many technologies and systems  Develop a global view of earth  For the challenge and adventure!  Why not?
• 3. BUT WHY MARS?  CLOSE TO EARTH  WARM AND LIGHT  LENGTH OF THE DAY  HAS SEASONS LIKE EARTH  RESOURCES –ATMOSPHERE,WATER AND METALS
• 4. INTRODUCTION  The possibility of life on Mars is a subject of significant interest to astrobiology due to the planet's proximity and similarities to Earth. To date no proof has been found of past or present life on Mars. However, cumulative evidence is now building that the ancient surface environment of Mars had liquid water and may have been habitable for microorganisms. The existence of habitable conditions does not necessarily indicate the presence of life.  Scientific searches for evidence of life began in the 19th century, and they continue today via telescopic investigations and landed missions.
• 6. MARS IN COMPARISON TO EARTH  Climate It has the largest dust storm in the solar system. Also it has seasons like earth like among all planet in the solar system. Mars temperature in winter is about -870c and in summer it is about -50c.  Speed Mars rotates at a speed of 14.5 miles per second those of earth is 18.5 mlies per second.  Length of the day Length of the day on mars is mostly 24 hrs and earth has 23 hrs 56 mintes 4.1 seconds.
• 7. POSSIBILITES  LIQUID WATER  Liquid water, necessary for life as we know it, cannot exist on the surface of Mars except at the lowest elevations for minutes or hours. Liquid water does not appear at the surface itself, but it could form in minuscule amounts around dust particles in snow heated by the Sun.  ATMOSPHERE  Consists of 95% of carbon dioxide, 3% of nitrogen, 1.6% of argon and trace of water and oxygen.
• 8. NASA plan to SEND LIFE to Mars to create oxygen before human colonisation  Plan to send microscopic organisms  In order to see if they can produce oxygen and therefore pave the way for humans to one day colonise Mars. The experiment follows successful laboratory tests on algae and bacteria and how they react with soil from Mars.NASA experimented in a specially-created "dummy Mars" to see if astronauts would be able to use microorganisms from Earth together with the surface of Mars to create life-sustaining oxygen.
• 9. NASA proposes a magnetic shield to protect Mars' atmosphere  The current scientific consensus is that, like Earth, Mars once had a magnetic field that protected its atmosphere. Roughly 4.2 billion years ago, this planet's magnetic field suddenly disappeared, which caused Mars' atmosphere to slowly be lost to space. This is due to solar winds on mars.  Over the course of the next 500 million years, mars went from being a warmer, wetter environment to the cold, uninhabitable place we know today.
• 10. In the future it is quite possible that an inflatable structure(s) can generate a magnetic dipole field at a level of perhaps 1 or 2 Tesla (or 10,000 to 20,000 Gauss) as an active shield against the solar wind.“ A dipole field positioned at Mars L1 Lagrange Point would be able to counteract solar wind, such that Mars' atmosphere would achieve a new balance. At present, atmospheric loss on Mars is balanced to some degree by volcanic outpassing from Mars interior and crust.
• 11. At one time, Mars had a magnetic field similar to Earth, which prevented its atmosphere from being stripped away.
• 12. Colonization  Colonization of Mars will require a wide variety of equipment—both equipment to directly provide services to humans and producion equipment used to produce food, propellant, water, energy and breathable oxygen—in order to support human colonization efforts.
• 13. Equipment needed for colonization COLONIZATION Storage facilities Resource extraction equipment's Energy and storage Food production equipment's Fuels 3D printers
• 14. FUTURE VISION  A greatly enhanced Martian atmosphere, in both pressure and temperature, that would be enough to allow significant surface liquid water would also have a number of benefits for science and human exploration in the 2040s and beyond. Much like Earth an enhanced atmosphere would:  allow larger landed mass of equipment to the surface.  shield against most cosmic and solar particle radiation.  extend the ability for oxygen extraction, and provide “open air” greenhouses to exist for plant production.  These new conditions on Mars would allow human explorers and researchers to study the planet in much greater detail and enable a truly profound understanding of the habitability of this planet. If this can be achieved in a lifetime, the colonization of Mars would not be far away.
• 15. EXPECTED RESULT  It has been determined that an average change in the temperature of Mars of about 40 C will provide  enough temperature to melt the CO2 over the northern polar cap.  The resulting enhancement in the atmosphere of this CO2,  a greenhouse gas, will begin,  the process of melting the water that is trapped in the northern polar cap of Mars.  It has been estimated that nearly 1/7th of the ancient ocean of Mars is trapped in the frozen polar cap.  Mars may once again become a more Earth-like habitable environment as shown in Figure. The results of these simulations will be reviewed and a projection of how long it may take for Mars to become an exciting new planet to study and to live on.  A future Mars protected from the direct solar wind should come to a new equilibrium allowing an extensive atmosphere to support liquid water on its surface.
• 16. The search for life on Mars may be our first chance to discover a second example of life and to investigate the biochemical properties of that life. This possibility is of fundamental importance from both a philosophical and science point of view. Determining where to look and how to search for evidence of a second genesis on Mars is therefore a key task for astrobiology in the next decade.

Life on Mars?

Sep 20, 2014

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Life on Mars?. Abhi Tripathi Andy Czaja ESS 250 Winter 2004. Agenda. The Indirect Evidence: Could life have arisen independently on Mars? Can life sustain itself on Mars at the present? Could life have been brought to Mars via panspermia? The Direct Evidence The ALH84001 controversy

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• viable organisms
• planetary surface
• direct evidence
• radioactive gas evolved
• metabolically produced labeled gas

Presentation Transcript

Life on Mars? Abhi Tripathi Andy Czaja ESS 250 Winter 2004

Agenda The Indirect Evidence: • Could life have arisen independently on Mars? • Can life sustain itself on Mars at the present? • Could life have been brought to Mars via panspermia? The Direct Evidence • The ALH84001 controversy • The Viking Labeled Release experiment vs. GCMS controversy

Could life have arisen independently on Mars?

What is LIFE? – A primer Life (as we know it) needs: • Energy • CHON • Water • Not much time to get going apparently! Obviously, Earth was sufficient, what about Mars?

Early Mars was similar to Earth

Energy can come from many sources Organic matter is ubiquitous in cosmos Carbonaceous chondrites [Cody et al., 2002] Mars only 11% mass of Earth [Sleep and Zahnle, 1998] Cooled to habitable levels earlier than Earth Atmosphere of several bars of CO2/N2 Thick enough and temperate enough to support liquid water Gullies and outflow channels indicate H2O

Can Life Sustain Itself on Mars at the Present? Analogues of Earth “diversitility”?

Potential Martians? Earth-life shows a wide range of metabolic variation • Heterotroph • Aerobes • SRBs • Methanogens • Phototrophs • Cyanobacteria • Photosynthetic bacteria • Lithotrophs • H2 oxidizers • Fe oxidizers • CH4 oxidizers [Nealson, 1997]

Extremeophiles • Earth organisms have resistance to extremes of: • Heat/cold [Stetter, 1996; Junge et al., 2004] • UV and ionizing radiation [Battista et al., 1999; Wynn-Williams et al., 1999] • Low water activity • Salinity • Low oxygen/no oxygen Can live deep within the Earth [Weiss et al., 2000] Mars, too?

Could Life Have Been Brought to Mars Via Panspermia?

Ejecta Theoretical analysis performed by Mileikowsky et. al 2000, find it overwhelmingly likely that any microorganisms living near the surface of a planet in our solar system would be transported to another planet inside the ejecta from an impact. Craterology and orbital trajectory simulations (Gladman et.al 1996) tell us that during the first 500-700 Ma, 0.7% of ejecta leaving Mars had hit the Earth 1Ma after impact and launch. But how much of that ejecta can sustain viable organisms?

Meet the Viable Organisms • Deinococcus Radiodurans • Bacillus Subtilis Deinococcus radiodurans's can withstand radiation 3,000 times what it would take to kill a human. That's 1.5 million rads of gamma radiation. Bacillus Subtilis’ which has been studied before with regards to its ability to survive in space (Webster & Greenberg 1985) *Note that there is no reason to believe that these bacteria were common on a primitive Earth or Mars, but they are common in nature today

Traumas • A trip from one planetary body to another would have four main threats to survival to the organisms: • Dynamical Stress • Excess Temperature • Radiation • Chemical Attack

Dynamical Stress & Excess Temperatures • Vikery & Melosh (1997) determine that a 1-30+ km impactor can propel rock off of a planetary surface and into space. • Upon impact the ground can boil up to 2800ºK • However reflected shock waves are phase shifted by 180º allowing some ejecta to remain totally or partially un-shocked, and the temperature to remain below 100º C • As and example, ALH84001 is believed to have not been heated above 40ºK (although some disagree with this conclusion) • When rising through the atmosphere, heating lasts less than 10s and does not permeate to the core, even though the exterior bores get baked.

Radiation • Organisms would have been subjected to UV, X-ray background, GCR, and Natural Radioactivity (which was much more potent in the first several 100 million years) • The combined Radiation effect is given by: τ(a)=ln(N°/Nd)/(σFGCR/a + σ FA/a) • The main factor in DNA damage in this case is the fact that the extreme cold slows down the metabolism, and therefore the DNA repair mechanisms of the bacteria. • Applying conservative numbers it was determined that a viable survival time of 100,000 years was reasonable for non-vacuated pores*. *Exposure to the Vacuum of space consistently demonstrated the lowest bacterial survival rate

Comprehensive Equation(Mileikowsky et. al, 2000) *Note the similarity in logic to the Drake Equation

Main Conclusions • Transfer of ejecta between planets was common during the first 0.5 Ga of our solar system. If RNA/DNA life existed on either or both Earth and Mars, then natural transfer of viable microorganisms was frequent. • After the first 0.5 Ga, transfer of ejecta continued at a lower rate and so did transfer of viable microorganisms.

The Problems of Panspermia • Could sufficiently robust organisms that could survive an interplanetary trip, (such as our two examples) have evolved on Mars or Earth in the first 500-700 Ma? • Can Mars sustain any life that had evolved on Earth after 3.8Ga? • Would any life brought from Mars to Earth after 3.8Ga survive for long in Earth’s eco-system (huge spacecraft design implications) • Biggest Problem: How do you PROVE Panspermia?

Evidence for life on Mars? YES! ALH84001 • Meteorite is from Mars • Carbonate globules of Martian origin • PAHs associated with carbonate globules • Magnetite crystals McKay et al., 1996 Thomas-Keprta et al., 2001 Friedmann et al., 2001

A closer look at the magnetite • 6 criteria for biogenicity of magnetite crystals [Thomas-Keprta et al., 2000]

5 criteria for biogenicity of magnetite chains [Friedmann et al., 2001] Uniform crystal size and shape within chains Gaps between crystals Orientation of elongated crystals Halo around chains Flexibility of chains A closer look at the magnetite

Evidence for life on Mars? NO!ALH84001 Granted • ALH84001 is from Mars • Features seen are not of terrestrial origin But, • Carbonates & magnetites could have been produced abiologically [Golden et al., 2001] • PAHs are ubiquitous in the cosmos • Magnetotactic bacteria recent invention on Earth [Nealson and Cox, 2002]

The Viking Labeled Release Experiment

The Proposal Detection of Metabolically Produced Labeled Gas: The Viking Mars Lander GILBERT V. LEVIN Biospherics Incorporated, Rockville, Maryland 20853 Received May 5, 1971 A qualitative, nonspecific method will test for life on Mars in 1976 by supplying radioactive substrates to samples of the planetary surface material. If microorganisms are present, they may assimilate one or more of the simple labeled compounds and produce radioactive gas. The compounds have been selected on the basis of biological theory and terrestrial results. The measurement of radioactive gas evolved as a function of time constitutes evidence for life. A control performed on a duplicate, but heat sterilized, sample will confirm the biological nature of the results. The shape of the response curve obtained from the viable sample may provide information on the physiological state and generation period of the organisms. Data obtained from a wide variety of terrestrial soils demonstrate a rapid response and high sensitivity for the experiment. Its ability to make comparative studies of soil microorganisms is also demonstrated. Instruments have been developed to conduct the experiment automatically and a breadboard version of the instrument designed for the Viking mission is under construction. The Mars experiment is described and simulated return data are given.

How Did It Work The labeled release (LR) experiment seeks to detect metabolism or growth through radiorespirometry. The radioactive nutrient used for the test consists of seven simple organic substrates (formate, glycolate, glycine, D- and L-alanine, D- and L-lactate), each present at 2.5 x 10-4 M and each equally and uniformly labeled with 14C (8 µc/µmole). • 0.5 cm3 of Mars soil is placed inside a test cell. • After 24hrs the sample was injected with 0.115ml of nutrient. • Approximately 7 sols after the first nutrient injection, a second nutrient injection was made, and incubation was continued for an additional 6 sols. • After each nutrient addition, radioactive gas evolved into the headspace above the sample equilibrated with the gas volume in the detector chamber and was measured. • A control sample was first sterilized, then given nutrient, and then had its evolved gas measured for metabolized 14C.

Results • The rate of gas evolution was constant until approximately 10% of the added radioactivity had been released (these observations were replicated several times at both Viking sites). • The sterilized control sample released virtually no gas, and one heated to 50 ºC evolved 60% less gas. • “The Labeled Release (LR) life detection experiment aboard NASA's 1976 Viking Mission reported results which met the established criteria for the detection of living microorganisms in the soil of Mars.” –Gilbert Levin

Yes! We Did Detect Life The GCMS is overrated! • Organics, including amino acids, have been found in meteorites from space. When a NASA spokesman was asked (Huntress, 1996) how this can be reconciled with Viking he replied that the GCMS was sent so long ago it may not have been sensitive enough to detect the low amounts of organic matter in the meteorite • The GCMS discovered no organics in a particular Antarctic soil that was KNOWN to have life (Levin, G. 1997).

The Oxides • Levin’s critic’s say: The atmosphere of Mars produces H2O2 that precipitates onto the Martian soil. The H2O2 and other oxidants produced are in the soil sample and thought to have oxidized the LR organic substrates to release radioactive gas. It was proposed that the oxidant(s) also released the oxygen detected in the Viking GEx experiment. This oxidative chemistry destroyed any organics or life. BUT: A study (Krasnopolsky, V., et. al 1997) of Earth-based IR telescopic measurements made through the entire column of the Martian atmosphere, showed no spectrographic feature for H2O2. H2O2 and other proposed derivatives do not approximate the thermal sensitivity of the Martian agent causing the LR responses. At 50°C, 90% H2O2 decomposes at only 0.001% per hour (Schumb, W.C et. al 1995). Of numerous attempts to simulate those results with H2O2, none reported has succeeded under conditions consistent with those on Mars.

The Anomalously Fast Rxn Skeptics Logic: If microorganisms were present on Mars they would be in far lesser numbers than in terrestrial soils. Hence, their response would be less, especially considering the harsh Mars environment. But look at the data:

It’s a Conspiracy • NASA did discover life on Mars in 1976 but scientists are just out-thinking themselves. • The results can be explained biologically • A comprehensive non-biological explanation cannot be duplicated. • No proof of an oxidative surface has EVER been shown, and this is the crux of the skeptics argument.

Labeled Release? – No! It’s a Sham Summary of dissenting opinions (Klein, 1999): • No organic compounds were found in Martian soil analyzed by the Viking Gas Chromatograph Mass Spectrometer (GCMS). (Biemann et al. 1976) • The regolith of Mars contains one or more oxidants responsible for decomposition of organic compounds supplied in the LR medium that can also be shown to be responsible for the immediate release of molecular oxygen.(Klein, 1978; Hunten 1978). KO2, ZnO2, Ca(O2)2 could all explain the release of Oxygen (Yen et. al. 1999) • The explanation in #2 above is consistent with #1 above (Biemann, 1977) • In an experiment where the LR nutrient mixture was added to UV irradiated hematite samples, 14CO2 was evolved. (Ponnamperuma et. al. 1977) • The kinetics of the experiment were duplicated when formate (an ingredient of the nutrient) was exposed to H2O2 and Fe2O3. (Oyama et. al. 1978) • Adding certain clay minerals to the LR nutrient resulted in many of the same findings seen in the experiment (Banin and Rishpon, 1979)

What kind of Microorganisms? Gilbert Levin further contends, “…a combination of known properties of microorganisms, perhaps even those possessed by a single species, could reproduce all aspects of the LR data.” This is a huge claim and Sagan once pointed out that the science community's stance should always be, “…the more extraordinary the claim, the more extraordinarily well tested the evidence must be.” • The initial rxn is so rapid and so intense that it would suggest a large biological load in the samples. • Viking’s organic analysis indicator was sensitive enough to detect 106 cells of E. Coli but didn’t detect anything. This should be detectable by GCMS Klein 1978

LR Experiment Conclusions • The LR experiment’s results demonstrated a chemical reaction and not a biological one. • The experiment was predicated on Earth-centric soil conditions, and could not have predicted the specific nature of the Martian soil, prior to the Viking landing. • Although the experiment did work as designed, its results can be explained by several natural reactions. • No biological analog can be found on Earth that can mimic all of the results seen. Furthermore, keep in mind that that any putative Martian organism was taken from its undisturbed natural environment and subjected to a “large” increase in temp in the ambient environment of the experiment, and yet continued metabolizing vigorously. • The vast majority of the science community does not accept the LR experiment as proof of life

Conclusion 1 • Evidence supports supposition of life existing on Mars • All of ALH84001 data put together (But especially the magnetite crystals) • Viking labeled release experiment • Tenacity of life

Conclusion 2 • There is no conclusive, direct evidence of life of Mars • Viking data inconclusive • ALH84001 evidence can all be explained by other means

References Battista, J.R., et al. (1999) Trends in Microbiology, v. 7(9): 362-365 Biemann, K., et al. (1976) Science, v. 194: 72 Cody, G.D., et al. (2002) Geochimica et Cosmochimica Acta, v. 66: 1851-1865 Friedmann, E.I., et al. (2001) PNAS, v. 98(5): 2176-2181 Golden, D.C., et al. (2001) American Mineralogist, v. 86: 370-375 Huntress, W., Speaking at NASA press conf., NASA HQ, Washington, Aug., 1996. Junge, K., et al. (2004) Applied and Environmental Microbiology, v. 70(1): 550-557 Klein, H.P. (1978) Icarus, v. 34: 666-674 Klein, H.P. (1999) Origins of Life and Evolution of the Biosphere, v. 29: 625-631 Krasnopolsky, V., et al. (1997) Journal of Geophysical Research, v. 102(E3): 6525-6534 Levin, G. Proceedings of Spie, SPIE-The International Society for Optical Engineering, Instruments, Methods, and Missions for the Investigation of Extraterrestrial Microorganisms. July-1 August 1997, San Diego, California McKay, C.P. (2003) Astrobiology, v. 3(2): 263-270 McKay, D.S., et al. (1996) Science, v. 273: 924-930 McKay, D.S., et al. (2002) Melosh, H.J. (1984) Icarus, v. 59: 234-260 Mileikowski, C., et al. (2000) Planetary and Space Science, v. 48: 1107-1115 Nealson, K.H. (1997) Annual Review of Earth and Planetary Science, v. 25: 403-434 Nealson, K.H., and B.L. Cox (2002) Current Opinion in Microbiology, v. 5: 296-300 Schopf, J.W. (1999) Cradle of Life, Princeton University Press, Princeton, NJ. 367pp. Schumb, W.C., et al. (1995), in Hydrogen Peroxide, p. 520, Am. Chem. Soc. Monograph Series, Reinhold Pub. Corp., NY. Stetter, K.O. (1996) FEMS Microbiology Reviews, v. 18: 149-158 Thomas-Keprta, K.L., et al. (2000) Thomas-Keprta, K.L., et al. (2001) PNAS, v. 98(5): 2164-2169 Weiss, B.P., et al. (2000) PNAS, v. 97(4): 1395-1399 Wynn-Williams, D.D., et al. (1999) European Journal of Phycology, v. 34: 381-391 Yen, A.S. et al. (1999) LPSC Conference

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NASA’s Mars 2020 Perseverance Rover Landing Animations

Animations for media and public use. This reel depicts key events during entry, descent, and landing that will occur when NASA’s Perseverance rover lands on Mars February 18, 2021. In the span of about seven minutes, the spacecraft slows down from about 12,100 mph (19,500 kph) at the top of the Martian atmosphere to about 2 mph (3 kph) at touchdown in an area called Jezero Crater.

Perseverance will seek signs of ancient microbial life on Mars, collect and cache Martian rock and regolith (broken rock and dust), characterize the planet's geology and climate, and pave the way for human exploration of the Red Planet.

For more animations and video of the NASA’s Mars 2020 Perseverance rover go to https://vimeo.com/420043274

For more information about Perseverance, visit https://mars.nasa.gov/perseverance

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A Nasa rover has reached a promising place to search for fossilised life on Mars

Chancellor's Fellow in Astrobiology, The University of Edinburgh

Disclosure statement

Sean McMahon has received funding from Nasa.

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

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While we go about our daily lives on Earth, a nuclear-powered robot the size of a small car is trundling around Mars looking for fossils. Unlike its predecessor Curiosity, Nasa’s Perseverance rover is explicitly intended to “search for potential evidence of past life”, according to the official mission objectives .

Jezero Crater was chosen as the landing site largely because it contains the remnants of ancient muds and other sediments deposited where a river discharged into a lake more than 3 billion years ago. We don’t know if there was life in that lake, but if there was, Perseverance might find evidence of it.

We can imagine Perseverance coming across large, well-preserved fossils of microbial colonies – perhaps resembling the cabbage-like “stromatolites” that solar-powered bacteria produced along ancient shorelines on Earth. Fossils like these would be big enough to see clearly with the rover’s cameras, and might also contain chemical evidence for ancient life, which the rover’s spectroscopic instruments could detect.

But even in such wildly optimistic scenarios, we wouldn’t be completely sure we’d found fossils until we could see them under the microscope in laboratories on Earth. That’s because it’s possible for geological features produced by non-biological processes to resemble fossils . These are referred as pseudofossils. That’s why Perseverance isn’t just looking for fossils in situ: it’s collecting samples. If all goes well, about 30 specimens will be returned to Earth by a follow-on mission, which is being planned in collaboration with the European Space Agency (Esa).

Earlier this month, Nasa announced that a particularly intriguing sample, the 24th for Perseverance and informally named “Comet Geyser”, had joined the rover’s growing collection. This one comes from an outcrop called Bunsen Peak, part of a rocky deposit called the Margin Unit that’s close to the crater’s edge.

This rock unit may have formed along the shoreline of the ancient lake . Rover instruments have shown that the Bunsen Peak sample is dominated by carbonate minerals (the main constituent of rocks like limestone, chalk and travertine on Earth).

The little carbonate grains are cemented together with pure silica (similar to opal or quartz). Nasa’s press release quotes Ken Farley, project scientist for Perseverance, saying: “This is the kind of rock we had hoped to find when we decided to investigate Jezero Crater.”

But what’s so special about carbonates? And what makes the Bunsen Peak sample particularly exciting from the point of view of astrobiology, the study of life in the Universe? Well, first, this rock may have formed under conditions that we would recognise as habitable: able to support the metabolism of life as we know it.

One ingredient in habitability is the availability of water. Carbonate and silica minerals can both form by direct precipitation from liquid water. Sample 24 may have precipitated from the lake water under temperatures and chemical conditions compatible with life, although there may be other possibilities that need to be tested. In fact, carbonate minerals are puzzlingly rare on Mars, which has always had plenty of CO₂ available.

In the wet environments of early Mars, that CO₂ should have dissolved in water and reacted to form carbonate minerals. Analysis of Bunsen Peak and of Sample 24 when it is sent to Earth, may eventually help us solve this mystery. One face of the outcrop has some interesting rough and streaky textures which could clarify its origins, but they are hard to interpret without more data.

Second, we know from examples on Earth that ancient sedimentary carbonates can yield wonderful fossils. Such fossils include stromatolites composed of carbonate crystals precipitated directly by bacteria. Perseverance hasn’t seen convincing examples of these.

There are some concentric circular patterns in the Margin Unit but they are almost certainly an effect of weathering. Even where stromatolites are absent, however, some ancient carbonates on Earth contain fossil colonies of microbial cells, which form ghostly sculptures where the original cellular structures have been replaced by minerals.

The small grain size of the “Comet Geyser” sample indicates a higher potential to preserve delicate fossils. Under some conditions, fine-grained carbonates can even retain organic matter —- the modified remains of the fats, pigments and other compounds that make up living things. The silica cement makes such preservation more likely: silica is generally harder, more inert, and less permeable than carbonate, and can protect fossil microbes and organic molecules inside rocks from chemical and physical alteration over billions of years.

When my colleagues and I wrote a scientific paper called A Field Guide to Finding Fossils on Mars in preparation for this mission, we explicitly recommended sampling fine-grained, silica-cemented rocks for these reasons. Of course, to crack open this sample and explore its secrets, we need to bring it back to Earth.

An independent review recently criticised Nasa’s plans for the return of samples from Mars as too risky, too slow, and too expensive. Modified mission architectures are now being evaluated to meet these challenges. In the meantime, hundreds of brilliant scientists and engineers at Nasa’s Jet Propulsion Laboratory in California lost their jobs because the US Congress effectively reduced funding for Mars sample return by failing to commit the necessary level of support.

Mars sample return remains Nasa’s highest planetary science priority and is strongly supported by the planetary science community around the world. The samples from Perseverance may revolutionise our view of life in the universe. Even if they don’t contain fossils or biomolecules, they will fuel decades of research and give future generations a completely new view of Mars. Let’s hope Nasa and the US government can live up to the name of their rover, and persevere.

• Astrobiology
• Space exploration
• Perseverance
• Outer space
• Mars exploration
• NASA Perseverance
• Search for alien life

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