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 The lake, located inside Gale Crater where the rover landed in
August 2012, likely covered an area 31 miles long and 3 miles wide,
though its size varied over time.
Analysis of sedimentary deposits gathered by NASA's Mars rover
Curiosity shows the lake existed for at least tens of thousands of
years, and possibly longer, geologist John Grotzinger, with the
California Institute of Technology in Pasadena, told reporters at
the American Geophysical Union conference in San Francisco.
"We've come to appreciate that is a habitable system of environments
that includes the lake, the associated streams and, at times when
the lake was dry, the groundwater," he said.
Analysis of clays drilled out from two rock samples in the area
known as Yellowknife Bay show the freshwater lake existed at a time
when other parts of Mars were dried up or dotted with shallow,
acidic, salty pools ill-suited for life.
In contrast, the lake in Gale Crater could have supported a simple
class of rock-eating microbes, known as chemolithoautotrophs, which
on Earth are commonly found in caves and hydrothermal vents on the
ocean floor, Grotzinger said.
Scientists also reported that the clays, which form in the presence
of water, were younger than expected, a finding that expands the
window of time for when Mars may have been suited for life.
Previous studies from Mars orbiters, landers and rovers have
provided increasing evidence for a warmer, wetter, more Earth-like
Mars in the planet's past. Ancient rocks bear telltale chemical
fingerprints of past interactions with water.
The planet's surface is riddled with geologic features carved by
water, such as channels, dried up riverbeds, lake deltas and other
sedimentary deposits.
New related studies on how much radiation blasts the planet set new
boundaries for how long any organic carbon, which so far has not
been found on Mars, could have been preserved inside rocks within
about 2 inches of the surface, the depth of Curiosity's drill.
But finding rock samples with relatively short exposure times should
not be a problem. An age-dating technique, used for the first time
on Mars, reveals that winds are sand-blasting away the rock faces at
Gale Crater.
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One of the mudstones at Yellowknife Bay, for example, has been
exposed to the destructive effects of cosmic rays for only about 70
million years, well within the period of time to detect organics,
said Don Hassler with the Southwest Research Institute in Boulder,
Colorado.
The Yellowknife Bay samples also showed hints of possible organics
that may have been destroyed in the rover's laboratory oven due to
highly oxidizing chemicals known as perchlorates, which so far seem
to be ubiquitous in the Martian soil.
Scientists will continue to look for rocks that may have higher
concentrations of organics or better chemical conditions for their
preservation, Grotzinger said.
"A key hurdle that we need to overcome is understanding how those
organics may have been preserved over time, from the time they
entered the rock to the time that we actually detect them," said
Curiosity scientist Jennifer Eigenbrode with NASA's Goddard Space
Flight Center in Greenbelt, Maryland.
Curiosity currently is en route to a three-mile high mound of
layered rock rising form the floor of Gale Crater, a formation known
as Mount Sharp.
Based on the new information gleaned from the Yellowknife Bay
samples, scientists are developing a new strategy to look for
organics there.
Even if life never started on Mars, organic material presumably
would have been deposited on the surface by crashing comets and
asteroids.
(Editing by Kevin Gray and Doina Chiacu)
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