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Image showing the Martian crater known as Gale Crater, which is approximately the size of Connecticut and Rhode Island combined.

Life on Mars could have been possible, based on findings from the Curiosity rover.

Photograph courtesy NASA/JPL-Caltech/ESA/DLR/FU Berlin/MSSS

Marc Kaufman

for National Geographic

Published December 9, 2013

A lake that could have supported life on Mars existed for as long as tens of thousands of years, NASA scientists announced Monday in a first-of-its kind discovery that revises our understanding of the red planet.

The fossil remains of the lake were identified not far from where the space agency's Curiosity rover landed inside Gale Crater on Mars in 2012, and where the rover science team has found chemical and mineral conditions needed for life, mission scientists said. (See also video: "Mission to Mars.")

As if that finding weren't dramatic enough, the scientists said that the ancient lake was one part of a watery Martian environment that also included streams and subsurface groundwater, which together formed a place where life could have survived for tens of millions of years. (See also: "Did Life on Earth Start on Mars?")

The dramatic conclusions announced today at the American Geophysical Union meeting in San Francisco by the Curiosity rover team, and reported in the journal Science, add substantially to the understanding of Gale Crater—a meteorite impact site that the Mars rover has been exploring—as a once-habitable environment, the first ever found on Mars.

"With this finding, we're a significant step closer to understanding how to locate environments on Mars that can support life," said project scientist John Grotzinger of NASA's Jet Propulsion Laboratory in Pasadena, California.

"We know there are signs that water pooled or flowed in many other locations on Mars, and now we can be more confident that they may well have been habitable, too," he said.

Curiosity Detour Becomes an Extended Stay

Yellowknife Bay, a small section of Gale Crater first described as suitable for ancient microbial life even before the surrounding lake was discovered, is located nearby the site where Curiosity landed in 2012.  Grotzinger said that the lake was likely miles long at its largest.

Exploring the area was never considered a primary goal for the rover. Curiosity had been scheduled to head instead for a three-mile-high peak inside Gale Crater known as Mount Sharp.

But an early detour to Yellowknife Bay proved to be a scientific bonanza, turning into a months-long stay.

The kind of microbes that could have survived the conditions of Gale Crater are known as chemolithotrophs—organisms that get their "food" from the electron transfer of chemical compounds in rocks. They can live without sunlight on Earth, and would potentially be similarly capable on Mars.

Grotzinger and others emphasized that, while concluding that Gale Crater was habitable is a major step forward in the search for possible extraterrestrial life, it does not necessarily mean that organisms ever actually lived there.

Curiosity is not a "life detection" mission, so it doesn't have the instruments needed to make that determination.

The Meaning of Clay

The conclusion that the Yellowknife area was once home to a lake is based on the make-up of the flat, soft, and broken-up mudstone that was discovered there. Earlier this year, Curiosity drilled into the mudstone in the first ever dig of its kind beyond Earth.

The key to the discovery was the detection of substantial amounts of clay in the stone—a mineral that can be formed only in the presence of water—in the stone.

Clay Points to Lake at Yellowknife Bay

The other key finding was that the clay formed at Yellowknife when it was covered by water, rather than being blown in or brought by a stream.

The proof involved the discovery that olivine, a mineral widely present on Mars, was greatly reduced in the mudstones. Under some climatic conditions and in the presence of water, olivine transforms into clay, said David Vaniman, a member of the Curiosity chemistry and mineralogy team.

There was a good amount of olivine in the first site Curiosity sampled–a sandy area called "Rocknest"–but there was almost none in the mudstones drilled later.

"That is a very strong signal saying that the clay was formed right there from the olivine, rather than being transported from elsewhere," Vaniman said. "And that means there was a lake."

Yellowknife Bay is a depression that is some 18 yards (17 meters) below the surface at the Curiosity's landing site.

While it looks now like the fossil remains of an ancient lake, Grotzinger said the formation itself is likely the creation of softer rocks being eroded over time. The area covered by water during the warmer and wetter early epoch of Mars history was likely much larger, he said.

Precisely dating when the lake existed in Gale has proved impossible, but Grotzinger said it most likely lasted well past the point when Mars has been traditionally considered capable of holding water on its surface.

The crater itself was formed by a large meteorite impact some 3.5 to 3.6 billion years ago, the scientists have concluded, and the water came in during millions or hundreds of millions of years that followed.

How a lake could exist this far into Martian history remains a scientific enigma. Traditional Mars science has held that the planet's atmosphere would have been largely destroyed eons before, making the planet much colder and theoretically unable to hold water at its surface because of the low air pressure.

By providing evidence showing that Gale Crater did have streams and a lake later in Mars history than expected, the Curiosity team has challenged long-held views about the planet.

The shift has potentially great implications for the question of how long parts of Mars might have been habitable, and is what Grotzinger called one of the major contributions of the Curiosity mission so far.

The paper by Grotzinger and dozens of his Curiosity colleagues concludes that it is "entirely plausible" that the kinds of once-habitable conditions found in rock formations at Yellowknife reach hundreds of yards below the surface, or piled up much higher before being eroded by the wind.

The conclusion that the area was likely habitable for up to tens of millions of years is based on calculations of how long it would take for that much sediment to be deposited into the area and then gradually turn to rock.

5 comments
joseph yechout
joseph yechout

Still desperately  searching  for proof that God does not exist.

Pierre Boisvert
Pierre Boisvert

Je suis du même avis que Louis Cruse il n'y a que pure spéculation sur la vie sur Mars ,Je pense que si il y a eu vie ou il y aura de la vie sur cette planète c'est lorsque nous enverrons de notre propre monde sur Mars ! D'ici la peut être aurons-nous de la visite d'ailleurs que sur Mars !!!

Louis Cruse
Louis Cruse

Nonsense ! There is not a single iota of evidence of "life" from Mars. Nor is there any evidence or test of any kind that starts "life" from inorganic material. Wishful thinking and really misleading scientific reporting, if it can be called scientific. Please leave such speculation to the National Enquirer and FOX News.

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