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New Type of Paleolake Spotted on Mars | Planetary Science, Space Exploration

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A 54-km- (33.5-mile) diameter Noachian-aged crater with neither inlet nor outlet channels is distinct from previously documented crater basin lakes on the planet, according to new research from Brown University.

Visible images with sketch maps showing major geologic features within as-yet unnamed crater mapped by Boatwright & Head: (a) the 54-km-diameter crater in the southern highlands of Mars (20.3°S, 42.6°E); no inlet or outlet breaches are observed; ridge networks (blue) begin near the crater wall base, where they are coincident with upslope-facing scarps (dashed lines) and crater wall alcoves; ridges terminate in two paleolake basins (cyan and green); (b) morphology of the eastern ridge network transitions downslope from dense proximal ridges to more widely spaced medial ridges; several medial ridges then converge into a single trunk ridge; (c) the southern ridge network terminates at three separate points along the margin of basin II. One of the ridges also displays an anabranching morphology. Image credit: Boatwright & Head, doi: 10.3847/PSJ/abe773.

Visible images with sketch maps showing major geologic features within as-yet unnamed crater mapped by Boatwright & Head: (a) the 54-km-diameter crater in the southern highlands of Mars (20.3°S, 42.6°E); no inlet or outlet breaches are observed; ridge networks (blue) begin near the crater wall base, where they are coincident with upslope-facing scarps (dashed lines) and crater wall alcoves; ridges terminate in two paleolake basins (cyan and green); (b) morphology of the eastern ridge network transitions downslope from dense proximal ridges to more widely spaced medial ridges; several medial ridges then converge into a single trunk ridge; (c) the southern ridge network terminates at three separate points along the margin of basin II. One of the ridges also displays an anabranching morphology. Image credit: Boatwright & Head, doi: 10.3847/PSJ/abe773.

The newly-discovered ‘closed-source drainage basin’ crater is located in the southern highlands of Mars.

It contains unusually well-preserved stream beds, ponds, and deposits, all of which formed completely inside the crater.

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.

“This is a previously unrecognized type of hydrological system on Mars,” said Ben Boatwright, a Ph.D. student in the Department of Earth, Environmental and Planetary Sciences at Brown University.

“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.”

Boatwright and his colleague, Brown University’s Professor Jim Head, were able to map out the details of the crater’s lake system using high-resolution images from NASA’s Mars Reconnaissance Orbiter.

The images revealed a telltale signature of ancient streambeds — features called inverted fluvial channels.

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

The researchers ruled out groundwater activity, as the crater lacked telltale sapping channels that form in groundwater systems.

These channels usually appear as short, stubby channels that lack tributaries — completely opposite from the dense, branching networks of inverted channels observed in the crater.

A careful examination of the crater wall also revealed a distinct set of ridges that face upward toward the crater wall.

The features are consistent with ridges formed where a glacier terminates and deposits mounds of rocky debris.

“Taken together, the evidence points to a glacier-fed system,” the scientists said.

They also identified more than 40 additional craters that appear to have related features.

“These new findings could be critical in understanding the climate of early Mars,” Professor Head said.

“We have these models telling us that early Mars would have been cold and icy, and now we have some really compelling geological evidence to go with it.”

“Not only that, but this crater provides the criteria we need to start looking for even more evidence to test this hypothesis, which is really exciting.”

The results were published in the Planetary Science Journal.

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Benjamin D. Boatwright & James W. Head. 2021. A Noachian Proglacial Paleolake on Mars: Fluvial Activity and Lake Formation within a Closed-source Drainage Basin Crater and Implications for Early Mars Climate. Planet. Sci. J 2 (52); doi: 10.3847/PSJ/abe773

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