As the Mars 2020 Perseverance rover continues to traverse Mars, all the talk remains around the Jezero crater. But now, researchers at Brown University in the US 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 the Planetary Science Journal earlier this month, a research team led by Ph.D. student Benjamin Boatwright describes an as-yet unnamed crater with some puzzling characteristics. According to an official release, 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 what could possibly be the source of this water?
In their findings, 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 release explains.
The type of lake described in this study is completely different from other Martian crater lakes, like those at Gale and Jezero craters, where Nasa rovers Curiosity and Perseverance are currently exploring.
“This is a previously unrecognized type of hydrological system on Mars,” Boatwright explains in the release. “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,” he says. “Everything is happening inside the crater, and that's very different than what’s been characterized before.”
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More importantly, the crater provides key clues about the early climate of the red planet. While it’s evident that the climate on Mars was once warmer and wetter than the frozen desert the planet is today, there’s less clarity on whether Mars had an Earthlike climate with continually flowing water 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 in the release. This new evidence of ancient glaciation could change that.
“The cold and icy scenario has been largely theoretical -- something that arises from climate models," he adds. “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.”
Boatwright was able to map out the details of the crater's lake system using high-resolution images taken by Nasa's Mars Reconnaissance Orbiter. These images revealed a common signature of ancient streambeds -- features called inverted fluvial channels.
He then worked with Jim Head, his advisor and a research professor at Brown University to rule out different possibilities of how the water entered this crater in the first place. Their investigations eventually pointed towards a glacier-fed system. Subsequent research has shown that this crater isn't the only one of its kind. At this month's Lunar and Planetary Science Conference, Boatwright presented research revealing more than 40 additional craters that appear to have related features, the release explains.
Nasa’s Perseverance rover, which landed on the planet in February, is currently exploring the Jezero crater. Scientists believe that around 3.5 billion years ago Jezero was home to a river that flowed into a lake, depositing sediment in a delta which is shaped like a fan. The rover will collect samples from the crater and prepare them for a possible round trip back to earth for further analysis. Using a drill to collect core samples of Martian rock and soil, Perseverance will then store them in sealed tubes for pickup by a future mission.
