National Geographic News
The find means that Columbus crater, in Mars's southern hemisphere, is the best place yet to study the chemistry of so-called fossil lakes on the red planet, the scientists say.
Hundreds of Martian craters have been identified as possible fossil lakes, based on the presence of now dry channels or sediments deposited at former deltas, said lead study author James Wray of Cornell University.
But new pictures from NASA's Mars Reconnaissance Orbiter have revealed that Columbus crater has alternating layers of hydrated minerals—clays and sulfates known to form only in the presence of water.
"Some lakes in western Australia that are relatively acidic and pretty salty show similar minerals to what we see in Columbus crater," Wray said.
What's more, the crater is one of the few proposed fossil lakes thought to have been fed entirely by groundwater, Wray added.
"If [the water] had come from rain, we would expect to see channels," Wray said. "But we don't."
Mars Crater Lake Born of Volcanic Warping?
Columbus crater dates back to Mars's Noachian epoch, a warm, wet period that lasted from about 4.6 to 3.5 billion years ago. (See pictures of what it might look like if we terraform modern Mars.)
Previously, researchers had thought another Noachian impact basin, Gusev crater, was the best example of a fossil lakebed, based on the crater's nearby channels and layered outcrops.
But when the Mars rover Spirit started exploring Gusev crater in 2004, the probe didn't find hydrated minerals, only volcanic basalt, Wray said.
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