Mars's Mysterious Craters May Be the Result of Long Lost Glacial Ice

Mars's mysterious craters, called double-layered ejecta craters (DLEs), may be the result of impacts onto a surface covered by a layer of glacial ice tens of meters thick.

Like other craters, DLEs are surrounded by debris excavated by an impactor. However, unlike their peers, they boast two distinct layers formed by debris -- a large outer layer with a smaller inner layer sitting on top.

Led by researchers at Brown University, the theory proposed in the new study corresponds with fresh evidence that Mars's climate was once very different from the one seen today.

"Recent discoveries by planetary geoscientists at Brown and elsewhere have shown that the climate of Mars has varied in the past," study author and geologist James W. Head said in a press release. "During these times, ice from the polar caps is redistributed into the mid-latitudes of Mars as a layer about 50 meters thick, in the same place that we see that the DLEs have formed."

This, he said, led them to hypothesize that ice could be the reason for DLE's second layer.

The way the researchers describe it happening is the impact blasts through the ice layer, spitting rock and other ejecta out onto the surrounding ice. However, because that ejected material falls onto slippery ice, it doesn't all stay there. Rather, material near the top of the upraised crater rim slides down on top of material on the lower slopes, creating the two-layer appearance.

"I think for the first time since DLEs were discovered in the 1970s we have a model for their formation that appears to be consistent with a very wide range of known data," co-author and graduate student David Kutai Weiss said.

Knowing this, the researchers argue, helps to reconstruct the environmental conditions at the time of the impacts.

"There are over 600 DLEs on the Martian surface, so reconciling how they formed with our knowledge of the climate of Mars is pretty important," Weiss said. "It could tell us a lot about the history of the martian climate on a global scale."