Researchers from Brown University have discovered a formerly obscure kind of ancient crater lake on Mars that could reveal hints about the planet's early climate.
In a study published in the 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 underneath.
So where did the water come from?
The researchers conclude that the framework was likely fed by spillover from a tragically missing 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 sort of lake described in this study differs starkly from other Martian crater lakes, similar to those at Gale and Jezero craters where NASA rovers are right now exploring.
"This is a formerly unrecognized sort of hydrological framework on Mars," Boatwright said. "In lake frameworks characterized up until this point, we see evidence of drainage coming from outside the crater, breaching the crater wall and in some cases flowing out the other side. Yet, that's not what is happening here. Everything is happening inside the crater, and that's altogether different than what's been characterized previously."
Importantly, Boatwright says, the crater provides key pieces of information 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, notwithstanding, is whether Mars had an Earthlike climate with continually flowing water for millennia, or whether it was generally cold and frosty with fleeting periods of warmth and melting. Climate simulations for early Mars recommend temperatures rarely peaking above freezing, yet geological evidence for cold and frigid conditions has been sparse, Boatwright says. This new evidence of ancient glaciation could change that.
"The cold and frigid scenario has been largely theoretical—something that arises from climate models," Boatwright said. "However, the evidence for glaciation we see here assists with bridging the gap among theory and observation. I think that's really the large takeaway here."
Boatwright was able to map out the details of the crater's lake framework using high-goal images taken by NASA's Mars Reconnaissance Orbiter. The images revealed a telltale signature of ancient streambeds—features called inverted fluvial channels. At the point when water streams across a rough surface, it can leave behind course-grained sediment inside the valley it erodes. At the point when these sediments interact with water, they can shape minerals that are harder than the surrounding rock. As further disintegration more than a long period of time shaves the surrounding rock away, the mineralized channels are abandoned as raised ridges spidering across the landscape. These features, along with sediment deposits and shoreline features, clearly show where water flowed and ponded on the crater floor.
Be that as it may, without any indication of an inlet channel where water entered the crater, "the inquiry turns out to be 'the means by which did these arrive?"' Boatwright said.
To sort it out, Boatwright worked with Jim Head, his advisor and a research teacher at Brown. They ruled out groundwater activity, as the crater lacked telltale sapping channels that structure in groundwater frameworks. These channels usually appear as short, stubby channels that lack tributaries—totally different from the dense, branching organizations of inverted channels observed in the crater. A careful examination of the crater wall also revealed a distinct arrangement of ridges that face upward toward the crater wall. The features are predictable with ridges formed where a glacier terminates and deposits mounds of rough debris. Taken together, the evidence points to a glacier-fed framework, the researchers concluded.