Mars is currently a dry and irradiated planet according to our robot friends, Perseverance and Curiosity. Evidence suggests that Mars was once a wet planet, however, there is substantial debate regarding Mars' origins and the life span of its long-lost bodies of water. 
Some theory suggests that it might have been because of active volcanoes that melted the Martian permafrost, while others suggest that it was because of a cataclysmic asteroid impact.

What Mars Is Like

<ul>
<li>Scientists believe that as long as there is a consistent source of water, life forms will be able to flourish. However, Mars' surface has been exposed to damaging solar and cosmic radiation, so the chances of life ever forming are largely reduced.</li>
<li>Unlike Earth, Mars did not have a relatively thick atmosphere nor did it have a strong magnetic field for it to end up like Earth.</li>
<li>With the lack of a magnetic sheath to protect it from the solar wind, Mars' atmosphere has been stripped away.</li>
</ul>

Inhabitable Mars

<ul>
<li>The question we have right now is that "can Mars host life now?" </li>
<li>We're still not sure yet. However, if we're not speaking about humanoids inhabiting Mars, then there might be a possible chance that there are already existing life forms already in Mars' subterranean reservoirs due to some evidence that there is liquid water locked away in it.</li>
<li>But for now, the red planet remains as an eerie time capsule of the era when Earth formed into what we know of it today.</li>
</ul>

Mars Hosting Life

<figure><picture><source media="(max-width: 599px) and (min-device-pixel-ratio: 3),(max-width: 599px) and (-webkit-min-device-pixel-ratio: 3),(max-width: 599px) and (min-resolution: 3dppx),(max-width: 599px) and (min-resolution: 288dpi)" srcset="https://static01.nyt.com/images/2020/07/28/science/28SCI-MARSLIFE1/28SCI-MARSLIFE1-mobileMasterAt3x-v2.jpg?quality=75&amp;auto=webp&amp;disable=upscale&amp;width=600"><source media="(max-width: 599px) and (min-device-pixel-ratio: 2),(max-width: 599px) and (-webkit-min-device-pixel-ratio: 2),(max-width: 599px) and (min-resolution: 2dppx),(max-width: 599px) and (min-resolution: 192dpi)" srcset="https://static01.nyt.com/images/2020/07/28/science/28SCI-MARSLIFE1/28SCI-MARSLIFE1-mobileMasterAt3x-v2.jpg?quality=75&amp;auto=webp&amp;disable=upscale&amp;width=1200"><source media="(max-width: 599px) and (min-device-pixel-ratio: 1),(max-width: 599px) and (-webkit-min-device-pixel-ratio: 1),(max-width: 599px) and (min-resolution: 1dppx),(max-width: 599px) and (min-resolution: 96dpi)" srcset="https://static01.nyt.com/images/2020/07/28/science/28SCI-MARSLIFE1/28SCI-MARSLIFE1-mobileMasterAt3x-v2.jpg?quality=75&amp;auto=webp&amp;disable=upscale&amp;width=1800"><img alt="" src="https://static01.nyt.com/images/2020/07/28/science/28SCI-MARSLIFE1/28SCI-MARSLIFE1-articleLarge-v2.jpg?quality=75&amp;auto=webp&amp;disable=upscale" srcset="https://static01.nyt.com/images/2020/07/28/science/28SCI-MARSLIFE1/28SCI-MARSLIFE1-articleLarge-v2.jpg?quality=90&amp;auto=webp 600w, https://static01.nyt.com/images/2020/07/28/science/28SCI-MARSLIFE1/28SCI-MARSLIFE1-jumbo-v2.jpg?quality=90&amp;auto=webp 1024w, https://static01.nyt.com/images/2020/07/28/science/28SCI-MARSLIFE1/28SCI-MARSLIFE1-superJumbo-v2.jpg?quality=90&amp;auto=webp 2047w" width="785" height="785"></picture><figcaption dir="auto">Credit...
Miguel Porlan</figcaption></figure>How habitable was early Mars? Why did it become less hospitable? And could there be life there now?<UL><LI><time datetime="2020-07-30T03:44:51-04:00">Published July 24, 2020</time><time datetime="2020-07-30T03:44:51-04:00">Updated July 30, 2020</time></LI></UL>Mars is the most explored planet in the solar system other than Earth. With all of our robotic visitors there, we’ve discovered that it is a world far too dry, cold and irradiated to support the scheming humanoids or tentacled invaders once imagined by science fiction.But our trips to Mars have opened a window into the deep past of the red planet, when conditions were far more conducive to life.This summer, NASA will launch its latest rover, <a href="https://www.nytimes.com/live/2021/02/18/science/nasa-mars-landing" title="" dir="ltr">Perseverance</a>, on a seventh-month journey to Mars. Like its predecessor, <a href="https://mars.nasa.gov/msl/home/" title="" rel="noopener noreferrer" dir="ltr">Curiosity</a>, Perseverance will touch down in the remains of an ancient Martian lake bed. What it finds there — along with missions launched by <a href="https://www.nytimes.com/2020/07/22/science/china-mars-mission.html" title="" dir="ltr">China</a> and the <a href="https://www.nytimes.com/2020/07/14/science/mars-united-arab-emirates.html" title="" dir="ltr">United Arab Emirates</a> — could help us Earthlings understand what Mars was like as a young planet some four billion years ago, and whether life ever blossomed on its surface.Advertisement<h2>How habitable was early Mars?</h2>It’s a serene image: A river flowing into an expansive lake that fills a crater basin. Waves lapping at the shoreline; sediment piling into a delta. A lake bed caked with clay.This is the type of aquatic environment that might support life, and it was once a familiar sight on Mars.“The evidence for the lakes and rivers is incontrovertible,” said Ken Farley, project scientist on Perseverance and a geochemist at the California Institute of Technology.Although Mars was once a wet planet, there is substantial debate about the origins, extent and life span of its long-lost bodies of water.AdvertisementFor instance, early Mars might have been warmed by <a href="https://www.nature.com/articles/ngeo2293" title="" rel="noopener noreferrer" dir="ltr">the gassy belches</a> of active volcanoes, which thickened its atmosphere and caused Martian permafrost to melt. Cataclysmic asteroid impacts might have also unleashed <a href="https://www.nytimes.com/2019/07/30/science/mars-tsunami-crater.html" title="" dir="ltr">900-foot mega-tsunamis</a> that flooded the planet’s terrain. There’s even disputed evidence that <a href="https://www.nytimes.com/2015/03/06/science/mars-had-an-ocean-scientists-say-pointing-to-new-data.html" title="" dir="ltr">an ocean once covered</a> its northern lowlands.“Was it weird, short, transient events, or was there an ocean?” Dr. Farley said. “I would say there’s no consensus. There’s a lot of ideas out there, and we really need a lot more data to sort it out.”One major question concerns the longevity of Mars’ liquid water. Nobody knows how much time is required for life to emerge on a planet, including on Earth. But the odds of life forming get better the longer that stable bodies of water persist.During Curiosity’s eight-year journey across Gale Crater, an ancient lake bed, the rover <a href="https://www.nasa.gov/feature/goddard/2020/nasa-s-curiosity-rover-finds-clues-to-chilly-ancient-mars-buried-in-rocks" title="" rel="noopener noreferrer" dir="ltr">discovered sediments</a> that suggest water was present for at least a few million years. Curiosity also detected organic compounds, key ingredients for life as we know it.“What we’ve learned from Curiosity suggests that Mars was habitable,” said Dawn Sumner, a planetary geologist at the University of California, Davis, and a member of the Curiosity science team.<figure><picture><source media="(max-width: 599px) and (min-device-pixel-ratio: 3),(max-width: 599px) and (-webkit-min-device-pixel-ratio: 3),(max-width: 599px) and (min-resolution: 3dppx),(max-width: 599px) and (min-resolution: 288dpi)" srcset="https://static01.nyt.com/images/2020/07/28/science/28SCI-MARSLIFE1-02/28SCI-MARSLIFE1-02-mobileMasterAt3x-v2.jpg?quality=75&amp;auto=webp&amp;disable=upscale&amp;width=600"><source media="(max-width: 599px) and (min-device-pixel-ratio: 2),(max-width: 599px) and (-webkit-min-device-pixel-ratio: 2),(max-width: 599px) and (min-resolution: 2dppx),(max-width: 599px) and (min-resolution: 192dpi)" srcset="https://static01.nyt.com/images/2020/07/28/science/28SCI-MARSLIFE1-02/28SCI-MARSLIFE1-02-mobileMasterAt3x-v2.jpg?quality=75&amp;auto=webp&amp;disable=upscale&amp;width=1200"><source media="(max-width: 599px) and (min-device-pixel-ratio: 1),(max-width: 599px) and (-webkit-min-device-pixel-ratio: 1),(max-width: 599px) and (min-resolution: 1dppx),(max-width: 599px) and (min-resolution: 96dpi)" srcset="https://static01.nyt.com/images/2020/07/28/science/28SCI-MARSLIFE1-02/28SCI-MARSLIFE1-02-mobileMasterAt3x-v2.jpg?quality=75&amp;auto=webp&amp;disable=upscale&amp;width=1800"><img src="https://static01.nyt.com/images/2020/07/28/science/28SCI-MARSLIFE1-02/28SCI-MARSLIFE1-02-articleLarge-v2.jpg?quality=75&amp;auto=webp&amp;disable=upscale" srcset="https://static01.nyt.com/images/2020/07/28/science/28SCI-MARSLIFE1-02/28SCI-MARSLIFE1-02-articleLarge-v2.jpg?quality=90&amp;auto=webp 600w, https://static01.nyt.com/images/2020/07/28/science/28SCI-MARSLIFE1-02/28SCI-MARSLIFE1-02-jumbo-v2.jpg?quality=90&amp;auto=webp 1024w, https://static01.nyt.com/images/2020/07/28/science/28SCI-MARSLIFE1-02/28SCI-MARSLIFE1-02-superJumbo-v2.jpg?quality=90&amp;auto=webp 2047w" width="600" height="600"></picture><figcaption dir="auto">Credit...
Miguel Porlan</figcaption></figure>Of course, “habitable” does not necessarily mean “inhabited.” The surface of Mars is exposed to damaging solar and cosmic radiation, which could have reduced the odds of complex, multicellular life ever forming.Advertisement“If life did exist on Mars, there would be a strong evolutionary force toward being resistant to radiation,” Dr. Sumner said.There are <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3685888/" title="" rel="noopener noreferrer" dir="ltr">microbial extremophiles</a> on Earth that can endure intense radiation, often healing their own DNA on the fly. So it’s not far-fetched to imagine that there might be Martian microbes that could tolerate an onslaught of radiation. Plus, they may have been able to retreat underground if conditions became particularly hostile at the surface.“The big lesson about life, from the revolution of being able to use DNA, is life is able to go everywhere,” Dr. Farley said. “It is amazing. It will fill every niche it can get itself into, and it will do it in a relatively short period of time.”<h2>Why did Mars become less habitable?</h2>The bygone oases of Mars are now mirages of a distant past, and modern Mars is a dried-up husk. Earth, in contrast, has been habitable to microbes for most of its life span and has positively burst at the seams with biodiversity for eons. Why did these sibling worlds experience such different outcomes?As baby planets, Mars and Earth were each swaddled in two protective blankets: a relatively thick atmosphere and a strong magnetic field. Earth has held on to both comforts. Mars has neither.Mars mysteriously lost its magnetic mojo <a href="https://www.theatlantic.com/science/archive/2015/10/mars-magnetic-field-ocean/409021/" title="" rel="noopener noreferrer" dir="ltr">billions of years</a> ago. With no magnetic sheath to protect it from solar wind, the Martian atmosphere <a href="https://www.washingtonpost.com/news/speaking-of-science/wp/2017/03/30/how-mars-lost-its-atmosphere-and-why-earth-didnt/" title="" rel="noopener noreferrer" dir="ltr">was stripped away</a> over time, though it still maintains a thin shell of its past skies.AdvertisementThese changes have left Mars relatively inert for billions of years, while Earth reinvents itself through tectonic activity, atmospheric shifts and the ingenuity of life.This is great news for Earthlings, as we need those processes to survive. Yet the sheer deadness of Mars over the past few billion years could make it easier to reconstruct its early history.“Life has been so successful on Earth that it’s hard to trace back its origin,” Dr. Sumner said. “On Earth, everything is covered with organic matter from modern life.”“One of the really cool and exciting things about Mars is that, because it doesn’t have plate tectonics, large parts of its surface have these super-old rocks,” she continued. “It’s a good place to go to try to understand what an early planet would be like.”<h2>Could Mars host life now?</h2>Robot explorers on Mars have turned up countless insights about the red planet, but they have never found clear-cut signs of creatures currently residing there. Life, at least as we know it on Earth, simply does not seem probable on the Martian surface.“If there’s any life on Mars now, it needs at least some liquid water,” Dr. Sumner said. “The surface of Mars now is very dry. Just incredibly dry. If there’s life on Mars now, it would be in the deep subsurface.”AdvertisementThere’s some <a href="https://www.nature.com/articles/s41561-020-0552-y" title="" rel="noopener noreferrer" dir="ltr">evidence that liquid water</a> is locked away in subterranean reservoirs, so perhaps there are sunless ecosystems lurking there. If these habitats exist, they are beyond the direct reach of our rovers and landers.Recent <a href="https://www.nytimes.com/2019/04/01/science/mars-methane-gas.html" title="" dir="ltr">detections of methane</a> and <a href="https://www.nytimes.com/2019/11/20/science/mars-oxygen-methane-curiosity-rover.html" title="" dir="ltr">other gases</a> in what’s left of Mars’ atmosphere are “a tantalizing potential signature,” Dr. Farley said, bolstering speculation about subterranean Martians. Many microbes on Earth produce methane, so it is possible that whiffs of the gas on Mars could be traced to alien life-forms deep underground.Curiosity, which is equipped with a methane-sensitive spectrometer, has compounded the mystery by <a href="https://www.nytimes.com/2019/06/22/science/nasa-mars-rover-life.html" title="" dir="ltr">recording weird spikes</a> of the gas at the Martian surface that remain unexplained.Unfortunately, the <a href="https://www.nytimes.com/2019/04/10/science/mars-methane-life.html" title="" dir="ltr">satellites orbiting the red planet have not been able to provide backup for these readings</a>, and the new NASA and Chinese rovers on the red planet may not be able to solve the puzzle.Methane can also be created by a wide range of natural processes that have nothing to do with life. Some experts, like Dr. Sumner, say that the presence of the gas on Mars is “not a surprise” because it has all the geological processes it needs to produce the gas without life.The discovery of life on Mars, either in the form of ancient fossils or subterranean reservoirs, would be one of the most momentous breakthroughs in human history. At last, we would have another example of a living planet, even if it only flourished in the past, implying that, at the very least, life can strike twice in the universe.But even if we never find Martians, “Mars is a place we can go to answer some of the questions about life on Earth,” Dr. Sumner said. The red planet remains an eerie time capsule of the era when life first sprouted on our own world, and the direction it could have gone had all the factors that made our world possible not turned out just the right way.Advertisement

How habitable was early Mars? Why did it become less hospitable? And could there be life there now?

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How habitable was early Mars? Why did it become less hospitable? And could there be life there now?

<ul><li><time datetime="2020-07-30T03:44:51-04:00">Published July 24, 2020 </time><time datetime="2020-07-30T03:44:51-04:00">Updated July 30, 2020 </time> </li> </ul>

Mars is the most explored planet in the solar system other than Earth. With all of our robotic visitors there, we’ve discovered that it is a world far too dry, cold and irradiated to support the scheming humanoids or tentacled invaders once imagined by science fiction.

But our trips to Mars have opened a window into the deep past of the red planet, when conditions were far more conducive to life.

This summer, NASA will launch its latest rover, <a dir="ltr" href="https://www.nytimes.com/live/2021/02/18/science/nasa-mars-landing" title="">Perseverance </a>, on a seventh-month journey to Mars. Like its predecessor, <a dir="ltr" href="https://mars.nasa.gov/msl/home/" rel="noopener noreferrer" title="">Curiosity </a>, Perseverance will touch down in the remains of an ancient Martian lake bed. What it finds there — along with missions launched by <a dir="ltr" href="https://www.nytimes.com/2020/07/22/science/china-mars-mission.html" title="">China </a>and the <a dir="ltr" href="https://www.nytimes.com/2020/07/14/science/mars-united-arab-emirates.html" title="">United Arab Emirates </a>— could help us Earthlings understand what Mars was like as a young planet some four billion years ago, and whether life ever blossomed on its surface.

It’s a serene image: A river flowing into an expansive lake that fills a crater basin. Waves lapping at the shoreline; sediment piling into a delta. A lake bed caked with clay.

This is the type of aquatic environment that might support life, and it was once a familiar sight on Mars.

“The evidence for the lakes and rivers is incontrovertible,” said Ken Farley, project scientist on Perseverance and a geochemist at the California Institute of Technology.

Although Mars was once a wet planet, there is substantial debate about the origins, extent and life span of its long-lost bodies of water.

For instance, early Mars might have been warmed by <a dir="ltr" href="https://www.nature.com/articles/ngeo2293" rel="noopener noreferrer" title="">the gassy belches </a>of active volcanoes, which thickened its atmosphere and caused Martian permafrost to melt. Cataclysmic asteroid impacts might have also unleashed <a dir="ltr" href="https://www.nytimes.com/2019/07/30/science/mars-tsunami-crater.html" title="">900-foot mega-tsunamis </a>that flooded the planet’s terrain. There’s even disputed evidence that <a dir="ltr" href="https://www.nytimes.com/2015/03/06/science/mars-had-an-ocean-scientists-say-pointing-to-new-data.html" title="">an ocean once covered </a>its northern lowlands.

“Was it weird, short, transient events, or was there an ocean?” Dr. Farley said. “I would say there’s no consensus. There’s a lot of ideas out there, and we really need a lot more data to sort it out.”

One major question concerns the longevity of Mars’ liquid water. Nobody knows how much time is required for life to emerge on a planet, including on Earth. But the odds of life forming get better the longer that stable bodies of water persist.

During Curiosity’s eight-year journey across Gale Crater, an ancient lake bed, the rover <a dir="ltr" href="https://www.nasa.gov/feature/goddard/2020/nasa-s-curiosity-rover-finds-clues-to-chilly-ancient-mars-buried-in-rocks" rel="noopener noreferrer" title="">discovered sediments </a>that suggest water was present for at least a few million years. Curiosity also detected organic compounds, key ingredients for life as we know it.

“What we’ve learned from Curiosity suggests that Mars was habitable,” said Dawn Sumner, a planetary geologist at the University of California, Davis, and a member of the Curiosity science team.

Of course, “habitable” does not necessarily mean “inhabited.” The surface of Mars is exposed to damaging solar and cosmic radiation, which could have reduced the odds of complex, multicellular life ever forming.

“If life did exist on Mars, there would be a strong evolutionary force toward being resistant to radiation,” Dr. Sumner said.

There are <a dir="ltr" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3685888/" rel="noopener noreferrer" title="">microbial extremophiles </a>on Earth that can endure intense radiation, often healing their own DNA on the fly. So it’s not far-fetched to imagine that there might be Martian microbes that could tolerate an onslaught of radiation. Plus, they may have been able to retreat underground if conditions became particularly hostile at the surface.

“The big lesson about life, from the revolution of being able to use DNA, is life is able to go everywhere,” Dr. Farley said. “It is amazing. It will fill every niche it can get itself into, and it will do it in a relatively short period of time.”

The bygone oases of Mars are now mirages of a distant past, and modern Mars is a dried-up husk. Earth, in contrast, has been habitable to microbes for most of its life span and has positively burst at the seams with biodiversity for eons. Why did these sibling worlds experience such different outcomes?

As baby planets, Mars and Earth were each swaddled in two protective blankets: a relatively thick atmosphere and a strong magnetic field. Earth has held on to both comforts. Mars has neither.

Mars mysteriously lost its magnetic mojo <a dir="ltr" href="https://www.theatlantic.com/science/archive/2015/10/mars-magnetic-field-ocean/409021/" rel="noopener noreferrer" title="">billions of years </a>ago. With no magnetic sheath to protect it from solar wind, the Martian atmosphere <a dir="ltr" href="https://www.washingtonpost.com/news/speaking-of-science/wp/2017/03/30/how-mars-lost-its-atmosphere-and-why-earth-didnt/" rel="noopener noreferrer" title="">was stripped away </a>over time, though it still maintains a thin shell of its past skies.

These changes have left Mars relatively inert for billions of years, while Earth reinvents itself through tectonic activity, atmospheric shifts and the ingenuity of life.

This is great news for Earthlings, as we need those processes to survive. Yet the sheer deadness of Mars over the past few billion years could make it easier to reconstruct its early history.

“Life has been so successful on Earth that it’s hard to trace back its origin,” Dr. Sumner said. “On Earth, everything is covered with organic matter from modern life.”

“One of the really cool and exciting things about Mars is that, because it doesn’t have plate tectonics, large parts of its surface have these super-old rocks,” she continued. “It’s a good place to go to try to understand what an early planet would be like.”

Robot explorers on Mars have turned up countless insights about the red planet, but they have never found clear-cut signs of creatures currently residing there. Life, at least as we know it on Earth, simply does not seem probable on the Martian surface.

“If there’s any life on Mars now, it needs at least some liquid water,” Dr. Sumner said. “The surface of Mars now is very dry. Just incredibly dry. If there’s life on Mars now, it would be in the deep subsurface.”

There’s some <a dir="ltr" href="https://www.nature.com/articles/s41561-020-0552-y" rel="noopener noreferrer" title="">evidence that liquid water </a>is locked away in subterranean reservoirs, so perhaps there are sunless ecosystems lurking there. If these habitats exist, they are beyond the direct reach of our rovers and landers.

Recent <a dir="ltr" href="https://www.nytimes.com/2019/04/01/science/mars-methane-gas.html" title="">detections of methane </a>and <a dir="ltr" href="https://www.nytimes.com/2019/11/20/science/mars-oxygen-methane-curiosity-rover.html" title="">other gases </a>in what’s left of Mars’ atmosphere are “a tantalizing potential signature,” Dr. Farley said, bolstering speculation about subterranean Martians. Many microbes on Earth produce methane, so it is possible that whiffs of the gas on Mars could be traced to alien life-forms deep underground.

Curiosity, which is equipped with a methane-sensitive spectrometer, has compounded the mystery by <a dir="ltr" href="https://www.nytimes.com/2019/06/22/science/nasa-mars-rover-life.html" title="">recording weird spikes </a>of the gas at the Martian surface that remain unexplained.

Unfortunately, the <a dir="ltr" href="https://www.nytimes.com/2019/04/10/science/mars-methane-life.html" title="">satellites orbiting the red planet have not been able to provide backup for these readings </a>, and the new NASA and Chinese rovers on the red planet may not be able to solve the puzzle.

Methane can also be created by a wide range of natural processes that have nothing to do with life. Some experts, like Dr. Sumner, say that the presence of the gas on Mars is “not a surprise” because it has all the geological processes it needs to produce the gas without life.

The discovery of life on Mars, either in the form of ancient fossils or subterranean reservoirs, would be one of the most momentous breakthroughs in human history. At last, we would have another example of a living planet, even if it only flourished in the past, implying that, at the very least, life can strike twice in the universe.

But even if we never find Martians, “Mars is a place we can go to answer some of the questions about life on Earth,” Dr. Sumner said. The red planet remains an eerie time capsule of the era when life first sprouted on our own world, and the direction it could have gone had all the factors that made our world possible not turned out just the right way.

3 Great Mysteries About Life on Mars

What Mars Is Like

Inhabitable Mars

Mars Hosting Life

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