Puzzling New Type of Ancient Crater Lake Discovered on Mars

Raised ridges spidering across the floor of a Martian crater were likely created by runoff from a long-lost glacier that once draped the planet’s southern highlands.
Credit: NASA

An ancient crater lake in the southern highlands of Mars appears to have been fed by glacial runoff, bolstering the idea that the Red Planet had a cold and icy past.

Researchers from Brown University have discovered a previously unknown type of ancient crater lake on Mars that could reveal clues about the planet’s early climate.

In a study published in Planetary Science Journal, a research team led by Brown Ph.D. student Ben Boatwright describes an as-yet unnamed crater with some puzzling characteristics. The crater’s floor has unmistakable geologic evidence of ancient stream beds and ponds, yet there’s no evidence of inlet channels where water could have entered the crater from outside, and no evidence of groundwater activity where it could have bubbled up from below.

So where did the water come from?

The researchers conclude that the system was likely fed by runoff from a long-lost Martian glacier. Water flowed into the crater atop the glacier, which meant it didn’t leave behind a valley as it would have had it flowed directly on the ground. The water eventually emptied into the low-lying crater floor, where it left its geological mark on the bare Martian soil.

The type of lake described in this study differs starkly from other Martian crater lakes, like those at Gale and Jezero craters where NASA rovers are currently exploring.

“This is a previously unrecognized type of hydrological system on Mars,” Boatwright said. “In lake systems characterized so far, we see evidence of drainage coming from outside the crater, breaching the crater wall and in some cases flowing out the other side. But that’s not what is happening here. Everything is happening inside the crater, and that’s very different than what’s been characterized before.”

Importantly, Boatwright says, the crater provides key clues about the early climate of Mars. There’s little doubt that the Martian climate was once warmer and wetter than the frozen desert the planet is today. What’s less clear, however, is whether Mars had an Earthlike climate with continually flowing water for millennia, or whether it was mostly cold and icy with fleeting periods of warmth and melting. Climate simulations for early Mars suggest temperatures rarely peaking above freezing, but geological evidence for cold and icy conditions has been sparse, Boatwright says. This new evidence of ancient glaciation could change that.

“The cold and icy scenario has been largely theoretical — something that arises from climate models,” Boatwright said. “But the evidence for glaciation we see here helps to bridge the gap between theory and observation. I think that’s really the big takeaway here.”

But without any sign of an inlet channel where water entered the crater, “the question becomes ‘how did these get here?”’ Boatwright said.

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