Thick Ice Sheet on Mars Reveals How Mysterious Craters Formed

It turns out that Mars may have some features that we weren't aware of. Scientists have announced that the Martian surface was once covered with a thick sheet of ice when more than 600 objects slammed into its surface.

The findings themselves come after the researchers puzzled over the presence of "double-layer ejecta" (DLE) on Mars. Like other craters, DLEs are surrounded by debris excavated by an impactor. What makes them different, though, is that the debris forms two distinct layers; there's a large outer layer and a smaller inner layer sitting on top. First seen in the 1970s, these DLEs have remained a mystery ever since. Yet now, scientists may have found the answer as to how these DLEs formed.

"Recent discoveries by planetary geoscientists at Brown and elsewhere have shown that the climate of Mars has varied in the past," said James Head, one of the researchers, in a news 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 made us think that this ice layer could be part of the explanation for the formation of the unusual DLE second layer."

The scientists performed some calculations and found that ice would have been a key ingredient when it came to the formation of DLEs. It's possible that the impacts blasted through a layer of ice, spitting rock and other eject out onto the surrounding ice. Because that ejected material sat on the slippery surface, though, it didn't all stay put. Instead, the material near the top of an upraised crater probably slid down the ice and overtopped material on the lower slopes. This may have helped create the two layer appearance.

 "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," said David Kutai Weiss, one of the researchers, in a news release. "It could tell us a lot about the history of the Martian climate on a global scale."

The findings are published in the journal Geophysical Research Letters.