All over the surface of Mars there are preserved features that tell the story of what Mars once looked like. These include canals carved by running water, delta compartments where sediment has been deposited over time, and lake beds where clay and hydrated minerals have been found. Studying these features can not only tell us more about Mars’ past, but also how Mars made the transition to what it is today.
According to new research by Brown Ph.D. Student Ben Boatwright, an unnamed Martian crater in the southern highlands of Mars, showed features that indicate the presence of water, but there is no indication of how it got there. Together with Brown professor Jim Head (his advisor), they concluded that the features of the crater are likely the result of runoff from a Martian glacier that once occupied the area.
The crater they investigated is located in the southern highlands of Mars, has a diameter of 54 km and dates from the Noachian era on Mars (approx. 4.1 to 3.7 billion years ago). Based on images captured by NASA’s Mars Reconnaissance Orbiter (MRO), Boatwright and Prof. Head mapped the crater floor and found features that unmistakably suggest that river beds and ponds once existed there.
Raised ridges spinning across the floor of a Mars crater were likely created by runoff from a long-lost glacier that once covered the planet’s southern highlands. Photo credit: NASA
However, this crater also showed no evidence of inlet channels through which water could have flowed into the crater, and no evidence of groundwater activity into which it could have seeped from below. As Boatwright said in a recent Brown University press release:
“This is a previously unrecognized type of hydrological system on Mars. In lake systems characterized so far, we see evidence that the drainage comes from outside the crater, breaks through the crater wall and in some cases flows out on the other side. But that doesn’t happen here. Everything happens in the crater, and that is very different from what was previously characterized. “
The features are known as inverted river channels, which are formed when water flows over rocky surfaces, leaving coarse-grained sediment in the channel it is carving. When these sediments interact with water, they can form minerals that are harder than the surrounding rock. After eons of erosion wear down these rocks, the mineralized channels remain as raised and branched ridges.
To determine how the water might have got there, Boatwright and Head first ruled out groundwater systems because the crater lacked the tell-tale sappa canals that form in their presence. These features generally appear as short, blunt channels with no tributaries that are very different from the dense, branching networks of inverted channels they have observed.
A topographic map shows the raised ridges (dark yellow) and low lying areas where water has accumulated (white). Photo credit: NASA / Boatwright et al./ Brown University
They also noted the presence of a specific series of ridges that point up towards the crater wall, which bear a remarkable resemblance to ridges on Earth that have formed on the edges of the glaciers. With these observations combined, they concluded that the crater’s inverted channels were created by a glacier-fed system that slowly deposited sediments and minerals over time.
Not only is this new hydrological system the first of its kind to be discovered, but it could also provide important clues about the early Martian climate. Scientists have known for some time that Mars was once warm enough to carry liquid water on its surface. However, it is still unclear whether the climate was mild enough for this water to flow continuously or whether it was mostly icy with intermittent melting periods.
In the past, scientists have run climate simulations that suggest early Mars had temperatures that were rarely above freezing. However, there is little geological evidence for these models. As Boatwright explained, this new evidence of ancient features associated with glacier runoff could change that.
“The cold and icy scenario was largely theoretical – something that emerges from climate models. But the evidence of icing we see here is helping to bridge the gap between theory and observation, ”he said. “I think this is really the big takeaway here.”
The researchers mapped where water flowed and accumulated in the crater floor. Photo credit: Boatwright et al./ Brown University
“We have these models that tell us that early Mars would have been cold and icy, and now we have some really compelling geological evidence for it,” Head added. “Not only that, but this crater provides the criteria we need to look for even more evidence to test this hypothesis, which is really exciting.”
What’s even more exciting is that this crater isn’t a unique find. During the 52nd Lunar and Planetary Science Conference (held online March 15-19), Boatwright presented subsequent studies that revealed more than 40 other craters that appear to have similar features. Her previous research was published in an article that appeared in the March 12 issue of the Planetary Science Journal.
Further reading: Brown University, The Planetary Science Journal
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