Great Lakes On Mars

Evidence mounts that the Red Planet may once have been wet--and alive

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We have long had reason to believe that the Mars we see today is not the Mars that once was. That bleak, freeze-dried world, most planetary scientists agree, was once a warm, wet place, running with rivers and sloshing with seas or oceans. None of that water remains, of course, but the riverbeds and basins stamped in the surface offer powerful arguments that it was there in abundance.

Now NASA has come up with the most striking evidence yet. The Mars Global Surveyor, which has been orbiting the Red Planet since 1997, has returned an album of images that show in brilliant detail outcroppings of layered rock, some more than two miles deep, that appear to be the remains of lake beds dating back more than 3.5 billion years. Why should lakes be important on a planet that we already knew had rivers and seas? Because the newly discovered formations precisely resemble the sedimentary depressions that have yielded some of Earth's richest fossil lodes. If life once thrived in the relatively warm bath of Mars' early lakes, these geological layer cakes are where we are most likely to find its remains.

It's impossible to determine from orbital images if any evidence of Martian life is actually hidden in the rocks. But the new pictures point to spots where robots or astronauts could one day land and dig--and perhaps find out for sure.

--By Jeffrey Kluger