presentation about life on mars

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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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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.

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/

nasa.gov/perseverance

News Media Contact

Jet Propulsion Laboratory, Pasadena, Calif.

818-393-9011

[email protected]

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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Planet Mars, explained

The rusty world is full of mysteries—and some of the solar system's most extreme geology. Learn more about Earth's smaller, colder neighbor.

The red planet Mars, named for the Roman god of war, has long been an omen in the night sky. And in its own way, the planet’s rusty red surface tells a story of destruction. Billions of years ago, the fourth planet from the sun could have been mistaken for Earth’s smaller twin, with liquid water on its surface—and maybe even life.

Now, the world is a cold, barren desert with few signs of liquid water. But after decades of study using orbiters, landers, and rovers, scientists have revealed Mars as a dynamic, windblown landscape that could—just maybe—harbor microbial life beneath its rusty surface even today.

Longer year and shifting seasons

With a radius of 2,106 miles, Mars is the seventh largest planet in our solar system and about half the diameter of Earth. Its surface gravity is 37.5 percent of Earth’s.

Mars rotates on its axis every 24.6 Earth hours, defining the length of a Martian day, which is called a sol (short for “solar day”). Mars’s axis of rotation is tilted 25.2 degrees relative to the plane of the planet’s orbit around the sun, which helps give Mars seasons similar to those on Earth. Whichever hemisphere is tilted closer to the sun experiences spring and summer, while the hemisphere tilted away gets fall and winter. At two specific moments each year—called the equinoxes—both hemispheres receive equal illumination.

But for several reasons, seasons on Mars are different from those on Earth. For one, Mars is on average about 50 percent farther from the sun than Earth is, with an average orbital distance of 142 million miles. This means that it takes Mars longer to complete a single orbit, stretching out its year and the lengths of its seasons. On Mars, a year lasts 669.6 sols, or 687 Earth days, and an individual season can last up to 194 sols, or just over 199 Earth days.

The angle of Mars’s axis of rotation also changes much more often than Earth's, which has led to swings in the Martian climate on timescales of thousands to millions of years. In addition, Mars’s orbit is less circular than Earth’s, which means that its orbital velocity varies more over the course of a Martian year. This annual variation affects the timing of the red planet’s solstices and equinoxes. On Mars, the northern hemisphere’s spring and summer are longer than the fall and winter.

There’s another complicating factor: Mars has a far thinner atmosphere than Earth, which dramatically lessens how much heat the planet can trap near its surface. Surface temperatures on Mars can reach as high as 70 degrees Fahrenheit and as low as -225 degrees Fahrenheit, but on average, its surface is -81 degrees Fahrenheit, a full 138 degrees colder than Earth’s average temperature.

Windy and watery, once

The primary driver of modern Martian geology is its atmosphere, which is mostly made of carbon dioxide, nitrogen, and argon. By Earth standards, the air is preposterously thin; air pressure atop Mount Everest is about 50 times higher than it is at the Martian surface . Despite the thin air, Martian breezes can gust up to 60 miles an hour, kicking up dust that fuels huge dust storms and massive fields of alien sand dunes.

Once upon a time, though, wind and water flowed across the red planet. Robotic rovers have found clear evidence that billions of years ago, lakes and rivers of liquid water coursed across the red planet’s surface. This means that at some point in the distant past, Mars’s atmosphere was sufficiently dense and retained enough heat for water to remain liquid on the red planet’s surface. Not so today: Though water ice abounds under the Martian surface and in its polar ice caps, there are no large bodies of liquid water on the surface there today.

Mars also lacks an active plate tectonic system, the geologic engine that drives our active Earth, and is also missing a planetary magnetic field. The absence of this protective barrier makes it easier for the sun’s high-energy particles to strip away the red planet’s atmosphere, which may help explain why Mars’s atmosphere is now so thin. But in the ancient past—up until about 4.12 to 4.14 billion years ago —Mars seems to have had an inner dynamo powering a planet-wide magnetic field. What shut down the Martian dynamo? Scientists are still trying to figure out.

High highs and low lows

Like Earth and Venus, Mars has mountains, valleys, and volcanoes, but the red planet’s are by far the biggest and most dramatic. Olympus Mons, the solar system’s largest volcano, towers some 16 miles above the Martian surface, making it three times taller than Everest. But the base of Olympus Mons is so wide—some 374 miles across—that the volcano’s average slope is only slightly steeper than a wheelchair ramp. The peak is so massive, it curves with the surface of Mars. If you stood at the outer edge of Olympus Mons, its summit would lie beyond the horizon.

Mars has not only the highest highs, but also some of the solar system’s lowest lows. Southeast of Olympus Mons lies Valles Marineris, the red planet’s iconic canyon system. The gorges span about 2,500 miles and cut up to 4.3 miles into the red planet’s surface. The network of chasms is four times deeper—and five times longer—than Earth’s Grand Canyon, and at its widest, it’s a staggering 200 miles across. The valleys get their name from Mariner 9, which became the first spacecraft to orbit another planet when it arrived at Mars in 1971.

A tale of two hemispheres

About 4.5 billion years ago, Mars coalesced from the gaseous, dusty disk that surrounded our young sun. Over time, the red planet’s innards differentiated into a core, a mantle, and an outer crust that’s an average of 40 miles thick.

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Its core is likely made of iron and nickel, like Earth’s, but probably contains more sulfur than ours. The best available estimates suggest that the core is about 2,120 miles across, give or take 370 miles—but we don’t know the specifics. NASA’s InSight lander aims to unravel the mysteries of Mars’s interior by tracking how seismic waves move through the red planet.

Mars’s northern and southern hemispheres are wildly different from one another, to a degree unlike any other planet in the solar system. The planet’s northern hemisphere consists mostly of low-lying plains, and the crust there can be just 19 miles thick. The highlands of the southern hemisphere, however, are studded with many extinct volcanoes, and the crust there can get up to 62 miles thick.

What happened? It’s possible that patterns of internal magma flow caused the difference, but some scientists think it's the result of Mars suffering one or several major impacts. One recent model suggests Mars got its two faces because an object the size of Earth’s moon slammed into Mars near its south pole.

Both hemispheres do have one thing in common: They’re covered in the planet’s trademark dust, which gets its many shades of orange, red, and brown from iron rust.

Cosmic companions

At some point in the distant past, the red planet gained its two small and irregularly shaped moons, Phobos and Deimos. The two lumpy worlds, discovered in 1877, are named for the sons and chariot drivers of the god Mars in Roman mythology. How the moons formed remains unsolved. One possibility is that they formed in the asteroid belt and were captured by Mars’s gravity. But recent models instead suggest that they could have formed from the debris flung up from Mars after a huge impact long ago.

Deimos, the smaller of the two moons, orbits Mars every 30 hours and is less than 10 miles across. Its larger sibling Phobos bears many scars, including craters and deep grooves running across its surface. Scientists have long debated what caused the grooves on Phobos. Are they tracks left behind by boulders rolling across the surface after an ancient impact, or signs that Mars’s gravity is pulling the moon apart?

Either way, the moon’s future will be considerably less groovy. Each century, Phobos gets about six feet closer to Mars; in 50 million years or so, the moon is projected either to crash into the red planet’s surface or break into smithereens.

Missions to Mars

Since the 1960s, humans have robotically explored Mars more than any other planet beyond Earth. Currently, eight missions from the U.S., European Union, Russia, and India are actively orbiting Mars or roving across its surface. But getting safely to the red planet is no small feat. Of the 45 Mars missions launched since 1960 , 26 have had some component fail to leave Earth, fall silent en route, miss orbit around Mars, burn up in the atmosphere, crash on the surface, or die prematurely.

More missions are on the horizon, including some designed to help search for Martian life. NASA is building its Mars 2020 rover to cache promising samples of Martian rock that a future mission would return to Earth. In 2020, the European Space Agency and Roscosmos plan to launch a rover named for chemist Rosalind Franklin , whose work was crucial to deciphering the structure of DNA. The rover will drill into Martian soil to hunt for signs of past and present life. Other countries are joining the fray, making space exploration more global in the process. In July 2020, the United Arab Emirates is slated to launch its Hope orbiter , which will study the Martian atmosphere.

Perhaps humans will one day join robots on the red planet. NASA has stated its goal to send humans back to the moon as a stepping-stone to Mars. Elon Musk, founder and CEO of SpaceX, is building a massive vehicle called Starship in part to send humans to Mars. Will humans eventually build a scientific base on the Martian surface, like those that dot Antarctica? How will human activity affect the red planet or our searches for life there?

Time will tell. But no matter what, Mars will continue to occupy the human imagination, a glimmering red beacon in our skies and stories.

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Life on Mars: Exploration & Evidence

When imagining locations where extraterrestrial life could potentially dwell, few places inspire the imagination like one of Earth's closest neighbors. For centuries, man has looked to Mars and imagined it as a home for other beings. Over the last fifty years, various missions to the red planet have sought to determine the probability of such an evolution. But how likely is life on Mars?

A habitable environment

When searching for life, most astrobiologists agree that water is key . All forms of terrestrial life require water, and while it is possible that life could evolve without the precious liquid, it is easier to search for conditions that are known to be optimal, rather than conditions we suppose could be." [ 5 Bold Claims of Alien Life  ]

This raises a problem on Mars. The planet today is dry and barren, with most of its water locked up in the polar ice caps . The planet's thin atmosphere allows radiation from the sun to irradiate the surface of the planet, adding to the environment's challenges. Evidence for water first showed up in 2000, when images from NASA's Mars Global Surveyor found gullies that appeared to have formed from flowing water.

But Mars wasn't always a desolate wasteland . Scientists think that, in the past, water may have flowed across the surface in rivers and streams, and that vast oceans covered the planet. Over time, the water was lost into space, but early conditions on the wetter planet could have been right for life to evolve. One estimate suggests that an ancient ocean could have covered as much as 19 percent of the planet's surface, compared to the 17 percent covered by Earth's Atlantic Ocean.

"With Mars losing that much water, the planet was very likely wet for a longer period of time than was previously thought, suggesting it might have been habitable for longer," said Michael Mumma, a senior scientist at Goddard, said in a statement .

It's also possible that liquid water flows on a modern Mars, either on the surface or beneath. The debate continues today on whether features known as recurring slope lineae (RSLs) form from ongoing water flows or running sand. "We've thought of RSL as possible liquid water flows, but the slopes are more like what we expect for dry sand," Colin Dundas of the U.S. Geological Survey's Astrogeology Science Center in Flagstaff, Arizona, said in a statement . "This new understanding of RSL supports other evidence that shows that Mars today is very dry.

Water beneath the surface may be even better for life. Underground water could shield potential life from harsh radiation. There's evidence for an ice deposit the size of Lake Superior. "This deposit is probably more accessible than most water ice on Mars, because it is at a relatively low latitude and it lies in a flat, smooth area where landing a spacecraft would be easier than at some of the other areas with buried ice," researcher Jack Holt of the University of Texas said in a statement .

Over the last four billion years, Earth has received a number of visitors from Mars . Our planet has been bombarded by rocks blown from the surface of the red planet, one of the few bodies in the solar system scientists have samples from. Of the 34 Martian meteorites, scientists have determined that three have the potential to carry evidence of past life on Mars.

A meteorite found in Antarctica made headlines in 1996 when scientists claimed that it could contain evidence of traces of life on Mars. Known as ALH 84001 , the Martian rock contained structures resembled the fossilized remains of bacteria-like lifeforms. Follow-up tests revealed organic material, though the debate over whether or not the material was caused by biological processes wasn't settled until 2012, when it was determined that these vital ingredients had been formed on Mars without the involvement of life .

"Mars apparently has had organic carbon chemistry for a long time," study lead author Andrew Steele, a microbiologist at the Carnegie Institution of Washington, told SPACE.com .

However, these organic molecules formed not from biology but from volcanism. Despite the rocky origin for the molecules, their organic nature may prove a positive in the hunt for life.

"We now find that Mars has organic chemistry, and on Earth, organic chemistry led to life, so what is the fate of this material on Mars, the raw material that the building blocks of life are put together from?" Steele said.

Scientists also found structures resembling fossilized nanobacteria on the Nakhla meteorite , a chunk of Mars that landed in Egypt. They determined that as much as three-fourths of the organic material found on the meteorite may not stem from contamination by Earth. However, further examination of the spherical structure, called an ovoid, revealed that it most likely formed through processes other than life.

"The consideration of possible biotic scenarios for the origin of the ovoid structure in Nakhla currently lacks any sort of compelling evidence," the scientists wrote in a study in the journal Astrobiology . "Therefore, based on the available data that we have obtained on the nature of this conspicuous ovoid structure in Nakhla, we conclude that the most reasonable explanation for its origin is that it formed through abiotic [physical, not biological] processes."

A third meteorite, the Shergotty, contains features suggestive of biofilm remnants and microbial communities.

"Biofilms provide major evidence for bacterial colonies in ancient Earth," researchers said in a 1999 conference abstract . "It is possible that some of the clusters of microfossil-like features might be colonies, although that interpretation depends on whether the individual features are truly fossilized microbes."

All of these samples provide tantalizing hints of the possibility of life in the early history of the red planet. But a fresh examination of the surface has the potential to reveal even more insights into the evolution of life on Mars.

Searching for life

When NASA set the first lander down on the Martian surface, one of the experiments performed sought traces for life. Though Viking's results were deemed inconclusive, they paved the way for other probes into the planet's environment. [ Mars Explored: Landers and Rovers Since 1971 (Infographic) ]

Exploration of Mars was put on hold for more than two decades. When examination of the planet resumed, scientists focused more on the search for habitable environments than for life, and specifically on the search for water. The slew of rovers, orbiters, and landers revealed evidence of water beneath the crust, hot springs — considered an excellent potential environment for life to evolve — and occasional rare precipitation. Although the Curiosity rover isn't a life-finding mission, there are hopes that it could pinpoint locations that later visitors might explore and analyze.

Future mission to Mars could include sample returns , bringing pieces of the Martian crust back to Earth to study. More experiments could be run by hand on Earth than can be performed by a remote robot explorer, and would be more controlled than meteorites that have lain on Earth.

"Mars 2020 will gather samples for potential return to Earth in the future. It's time for the sample-analysis community to get serious about defining and prioritizing Mars sample science, and in helping to make the case for the future missions that would get those samples home," David Beaty, co-leader of NASA's Returned Sample Science Board and chief scientist for the Mars Exploration Directorate at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, said at a 2017 workshop .

But the hunt for Martian life may be stymied by concerns over how to prevent infecting the Red Planet with Earth life. Current international policies impose heavy financial burdens that make exploring potentially habitable regions of Mars an extra challenge.

"Bottom line is that a thorough cleaning of a spacecraft aimed to in situ search for life on a special region of Mars today would easily cost around $500 million," Dirk Schulze-Makuch told SPACE.com via email. Schulze-Makuch, a researcher at Washington State University, and his colleague Alberto Fairen of Cornell University authored a commentary article published in the journal Nature Geoscience arguing for less-strict protection measures for Mars.

"With that amount of money, you can entirely finance a 'Discovery-type' mission to Mars, similar to Pathfinder or InSight," he added. "Therefore, if we'd relax planetary protection concerns in a Viking-like mission today, we could add another low-budget mission to the space program."

Are we the Martians?

The transfer of material from Mars to Earth and presumably back again has sparked some debate about the possibility of contamination early in the history of life. Some scientists argue that a meteorite from Earth could have traveled to Mars — or vice versa. Debates rage over whether or not tiny organisms would be hardy enough to survive the voyage through a freezing, airless, radiation-filled vacuum and kick off life at its new home.

The idea of such seeding is not limited to interactions with Mars. Some have proposed that debris from outside the solar system could even be responsible for spawning life on Earth. But in terms of the Red Planet, it is possible that scientists might one day find life on Mars — and it could be a close relation.

"If we find life on another planet, will it be truly alien or will it be related to us? And if so, did it spawn us or did we spawn it?" researcher Dina Pasini, of the University of Kent, questioned in a statement . "We cannot answer these questions just now, but the questions are not as farfetched as one might assume."

Follow Nola Taylor Redd at @NolaTRedd , Facebook , or Google+ . Follow us at @Spacedotcom , Facebook or Google+ .

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Nola Taylor Tillman is a contributing writer for Space.com. She loves all things space and astronomy-related, and enjoys the opportunity to learn more. She has a Bachelor’s degree in English and Astrophysics from Agnes Scott college and served as an intern at Sky & Telescope magazine. In her free time, she homeschools her four children. Follow her on Twitter at @NolaTRedd

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Mission Overview: NASA’s Perseverance Mars Rover

NASA's Mars 2020 Perseverance Rover is heading to the Red Planet to search for signs of ancient life, collect samples for future return to Earth and help pave the way for human exploration. The rover will carry with it several technology demonstrations including a helicopter, which will attempt humanity's first powered flight on another planet. Perseverance has a new set of science instruments and the ability to “self-drive” on the Martian surface.

The Perseverance rover is scheduled to launch from Space Launch Complex 41 at NASA’s Kennedy Space Center as early as July 30. It is set to land at Mars' Jezero Crater on Feb. 18, 2021.

For more information on Mars 2020, visit: nasa.gov/perseverance and mars.nasa.gov/perseverance

- [Woman] You know Mars is the closest place that we can reach with robotic exploration that we think had a really good chance of having ancient life.

- [Man] The Perseverance Rover will land at a location called Jezero Crater. Jezero Crater is a very interesting place. It's a crater that once held a lake.

- [Woman] There are a lot of craters on the surface of Mars that could have once hosted ancient lakes. But not ever crater that we think had a lake, actually preserves evidence that that lake was there.

- [Man] It had an inflow channel and it had an outflow channel. That means it was filled, the crater was filled with water.

- [Woman] In Jezero, we have probably one of the most beautifully preserved delta deposits on Mars in that crater.

- [Man] This is a wonderful place to live for micro organisms, and it is also a wonderful place for those micro-organisms to be preserved so that we can find them now so many billions of years later.

- There is no other place on Mars that has the unique combination of the lake setting, the beautifully preserved delta and the diverse mineralogy that we have in Jezero Crater. So it's truly a special landing site.

- The major goal of the Perseverance mission is to investigate astrobiology on Mars in particular, to address the question of whether life ever existed on Mars. The Perseverance Rover starts with a design that's very similar to Curiosity. But we added to it a whole new set of science instruments. And these science instruments were purposefully selected to help us in the search for bio signatures.

- We're gonna be taking microphones with us. For the first time, we're gonna have that human sense on another planet.

- Perseverance carries with her a grand experiment in space fairing technology. A helicopter, the name of which is now Ingenuity.

- One of the major upgrades that Perseverance has from Curiosity is that it's able to self drive for a distance of up to 200 meters per day. As the rover is driving, it's literally building the map of the road it's driving on on Mars.

- Scientists for years have told us that to really unlock the secrets of Mars, we have to bring samples from Mars back to Earth.

- [Man] So what Mars 2020 is going to do is to drill samples, put them in small tubes, we're gonna seal it in it's own individual tube. We set them on the surface to provide a target for the second ignitions. Which hopefully will get into development in the next several years. And could potentially get the samples back to Earth by 2031.

- [Man] Perseverance is a very, very profound first step in both our understanding of our place in the universe and a stepping stone towards human exploration on Mars.

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THE ROAD TO MAKING HUMANITY MULTIPLANETARY

“You want to wake up in the morning and think the future is going to be great - and that’s what being a spacefaring civilization is all about. It’s about believing in the future and thinking that the future will be better than the past. And I can’t think of anything more exciting than going out there and being among the stars.”

At an average distance of 140 million miles, Mars is one of Earth's closest habitable neighbors. Mars is about half again as far from the Sun as Earth is, so it still has decent sunlight. It is a little cold, but we can warm it up. Its atmosphere is primarily CO2 with some nitrogen and argon and a few other trace elements, which means that we can grow plants on Mars just by compressing the atmosphere. Gravity on Mars is about 38% of that of Earth, so you would be able to lift heavy things and bound around. Furthermore, the day is remarkably close to that of Earth.

SpaceX’s Starship spacecraft and Super Heavy rocket – collectively referred to as Starship – represent a fully reusable transportation system designed to carry both crew and cargo to Earth orbit, the Moon, Mars and beyond. Starship is the world’s most powerful launch vehicle ever developed, capable of carrying up to 150 metric tonnes fully reusable and 250 metric tonnes expendable.

To Mars and back

Together the Starship spacecraft and Super Heavy rocket create a reusable transportation system capable of on orbit refueling and leveraging Mars’ natural H2O and CO2 resources to refuel on the surface of Mars.

Starship launches with Starship Super Heavy booster. Booster separates, returning to Earth.

Starship enters Earths orbit while a refilling tanker launches to mate with Starship in orbit.

Tanker ship docks with Starship, refilling Starship and returning to Earth.

Once Starship has been fully refueled, it will begin its journey from Earth orbit, around the Sun and onward to Mars.

When Starship lands on Mars it will be refueled using Mars local resources of H20 and CO2.

When Starship is fully refueled it will begin Mars ascent and direct return to Earth.

ON-ORBIT REFILLING

Starship leverages tanker vehicles (essentially the Starship spacecraft minus the windows) to refill the Starship spacecraft in low-Earth orbit prior to departing for Mars. Refilling on-orbit enables the transport of up to 100 tons all the way to Mars. And if the tanker ship has high reuse capability, the primary cost is just that of the oxygen and methane, which is extremely low.

LANDING ON MARS

Starship will enter Mars’ atmosphere at 7.5 kilometers per second and decelerate aerodynamically. The vehicle’s heat shield is designed to withstand multiple entries, but given that the vehicle is coming into Mars’ atmosphere so hot, we still expect to see some ablation of the heat shield (similar to wear and tear on a brake pad). The engineering video below simulates the physics of Mars entry for Starship.

For inquiries about our human spaceflight program, contact [email protected]

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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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Mars remains our horizon goal for human exploration because it is one of the only other places we know where life may have existed in the solar system. What we learn about the Red Planet will tell us more about our Earth’s past and future, and may help answer whether life exists beyond our home planet. Like the Moon, Mars is a rich destination for scientific discovery and a driver of technologies that will enable humans to travel and explore far from Earth.

33 million to 249 million miles from Earth (always changing)

Miles(roundtrip)

-284 degrees F to 86 degrees F

Six Technologies to Get Humans to Mars

NASA is advancing many technologies to send astronauts to Mars as early as the 2030s. Here are six things we are working on right now to make future human missions to the Red Planet possible.

Preparing for Mars

Engineers and scientists around the country are working to develop the technologies astronauts will use to one day live and work on Mars and safely return home to Earth.

Quick Facts

Periodic dust storms on Mars can last for months, making nuclear fission power a more reliable option than solar power. 

Temperatures on Mars can range from -284 degrees F to 86 degrees F. The atmosphere on Mars is 96% carbon dioxide.

One day on Mars lasts about 37 minutes longer than an Earth day. A year on Mars is almost twice as long as a year on Earth.

Gravity on Mars is about one-third of the gravity on Earth. If you weigh 100 pounds on Earth, you would weigh 38 pounds on Mars.

Mars has two moons: Phobos and Deimos. Phobos is 13.8 miles across, and Deimos is 7.8 miles across.

Getting There and Back

When astronauts travel to Mars and back, their vehicle will return home with more than a billion miles on its odometer — more than a thousand times the distance that Artemis I traveled.

Living and Working on Mars

The Mars Oxygen In-Situ Resource Utilization Experiment, or MOXIE, is helping NASA prepare for human exploration of Mars by demonstrating the technology to produce oxygen from the Martian atmosphere for burning fuel and breathing.

Astronauts on a roundtrip mission to Mars will not have the resupply missions to deliver fresh food. NASA is researching food systems to ensure quality, variety, and nutritional values for these long missions. Plant growth on the International Space Station is helping to inform in-space crop management as well.

NASA is developing life support systems that can regenerate or recycle consumables such as food, air, and water and is testing them on the International Space Station.

Like we use electricity to charge our devices on Earth, astronauts will need a reliable power supply to explore Mars. The system will need to be lightweight and capable of running regardless of its location or the weather on the Red Planet. NASA is investigating options for power systems, including fission surface power.

Spacesuits are like “personal spaceships” for astronauts, protecting them from harsh environments and providing all the air, water, biometric monitoring controls, and communications needed during excursions outside their spaceship or habitat.

Communications

Human missions to Mars may use lasers to stay in touch with Earth. A laser communications system at Mars could send large amounts of real-time information and data, including high-definition images and video feeds.

An astronaut's primary shelter on Mars could be a fixed habitat on the surface or a mobile habitat on wheels. In either form, the habitat must provide the same amenities as a home on Earth — with the addition of a pressurized volume and robust water recycling system.

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Together with our partners, we will pioneer Mars and answer some of humanity’s fundamental questions: Was Mars home to microbial life? Is it today? Could it be a safe home for humans one day? What can it teach us about life elsewhere in the cosmos, or how life began on Earth? What can it teach us about Earth’s past, present, and future?

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Paleoenvironmental context in searching for past life on Mars

Professor Kathy Campbell

Abstract:   The search for life beyond Earth occupies exploration efforts of space agencies and researchers, and captures the imagination of the public. Mars is a top Solar System candidate in this quest because of its multiple, once habitable environments of surface liquid water that may have harboured microbial life at a time when Earth’s own biosphere was getting underway billions of years ago. Yet, validation of possible signals of past life in Martian rocks will likely require sample return as well as study of multiple lines of evidence from within well constrained contextual settings to identify biosignatures – i.e. distinctive suites of durable textural, mineralogical, and chemical indicators of life. Focusing on Earth’s hot spring deposits and unusual hydrothermal silica found by Spirit rover at Columbia Hills on Mars, this talk takes a comparative paleoenvironmental approach to help narrow the search and potentially reveal the arguably best place in the Solar System to discover (fossil) life – version 2.0.

Professor Kathy Campbell (UW M.S., USC Ph.D.) is a geologist, paleoecologist and astrobiologist investigating extreme (paleo)environments, particularly hot springs and cold seeps as analogue settings for early life on Earth and possible life elsewhere in the Solar System. Her university studies were undertaken in the western U.S., followed by a National Research Council/NASA post-doctoral appointment at NASA Ames Research Center, before she joined The University of Auckland in 1997. She is an elected Fellow of the Royal Society of New Zealand Te Apārangi, and is founding Director of Te Ao Mārama – Centre for Fundamental Inquiry, a transdisciplinary research center exploring the origin and evolution of the Universe and its life. Professor Campbell was an invited senior research fellow at the Le Studium Institute for Advanced Studies in France, and a distinguished lecturer in international astrobiology schools in Spain and Thailand. In NASA’s Mars 2020 landing site selection process, her team’s proposal made it into the final three, with the aim to collect samples of potential Martian biosignatures from a >3.5-billion-year-old hydrothermal deposit at Columbia Hills in Gusev crater, preparing for their future return to Earth.

Here’s some exciting news. I guess. It appears that until 3 billion years ago, Mars was partly covered by water, at which time its atmosphere was blown away by the solar wind. But a recent study published in the Proceedings of the National Academy of Sciences indicates that an enormous amount of water is still trapped in the pores of volcanic rock beneath the surface of Mars.

Water implies the possibility of life. Michael Manga, study coauthor and professor at the University of California, Berkeley, says: “Water is necessary for life as we know it. I don’t see why (the underground Martian reservoir) is not a habitable environment. It’s certainly true on Earth — deep, deep mines host life, the bottom of the ocean hosts life.”

What would it mean if we found life on Mars, even if it’s only primitive organisms similar to those that we find at the bottom of the ocean on Earth?

Neel V. Patel argued recently in the New York Times that the discovery of life on Mars “would change how humanity thinks about its place in this universe.” He concedes that sending humans to extraterrestrial destinations is a worthy goal, but NASA’s top priority should be answering the question of whether we are truly alone in the universe.

Patel’s point is well taken, but, really, does it matter? It might be interesting and surprising to find life on Mars, but would it change anything having to do with who we are and our place in the universe?

In fact, concerns about life and water and other resources on the moon, Mars and elsewhere bear this inherent danger: They distract our attention away from the one place in the entire universe where we know, for sure, that more-or-less intelligent life does exist, as well as the unfortunate fact that we’ve currently put it into considerable jeopardy.

Humankind’s imagination has always been excited by the possibility that the cosmos harbors life beyond Earth. We’ve been pleased to entertain the idea that the moon, Mars and other planets are way stations on the path to our inherent destiny, to conquer space and to colonize distant moons and planets.

Accordingly, Earth’s most prominent visionary, Elon Musk, is committed to landing humans on Mars within 10 years and founding a metropolis of a million earthlings on the Red Planet within 20.

This ambitious goal is admittedly consistent with the narrative that has driven human migration since our ancestors left Africa some 80,000 years ago. Humans have regularly moved into new territory, thrived, consumed and outgrown their resources and then moved on and repeated the cycle. According to this narrative, as our planet increasingly shows the stress of our overuse, colonization of the moon and Mars is the next logical step.

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But is it? Once we leave the Earth, does this terrestrial narrative make sense, if it ever did?

In 1492 the so-called New World must have seemed unimaginably distant from Europe. But it wasn’t, and it wasn’t really New. It was still a place where humans could thrive.

But the universe is different. Our Milky Way is an average-size galaxy in a universe that contains, by some estimates, 2 trillion others. Still, the Milky Way is 100,000 light-years across. If our galaxy were reduced to the size of the United States, on that scale, our solar system would be the size of a quarter in your change tray.

In short, the scale of travel beyond the Earth is immense enough to make nonsense of whatever logic drove the narrative that spread humankind across the globe. This makes sense: We evolved here. The Earth created us. And now we’re creating whatever the Earth is going to become. The Earth is where our lives make sense.

Of course, critics will say that this sort of thinking would have kept our ancestors cringing in caves, terrified of venturing onto the savannas. Maybe. But to imagine that we can escape an overburdened Earth by colonizing Mars is a fantasy at odds with our essential humanity.

Life on Mars? Good luck to it. We’ve got our own problems here.

John M. Crisp lives in Texas. Contact him at [email protected] .

©2024 Tribune Content Agency LLC

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