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Big Ice May Explain Mars’ Double-Layer Craters

August 7, 2013
An odd type of crater

Double-layer ejecta craters could form when ejected material slides down steep crater walls and across ice, forming a top layer. Striations, common in landslides on Earth, radiate out from the crater rim. Credit: NASA

Brown planetary geologists, including graduate student David Kutai Weiss, have an explanation for the formation of more than 600 “double-layer ejecta” (DLE) craters on Mars. The Martian surface was covered with a thick sheet of ice at impact. Ejected material would later slide down steep crater sides and across the ice, forming a second layer.

Double-layered ejecta craters or DLEs, like other craters, are surrounded by debris excavated by an impactor. What makes DLEs different is that the debris forms two distinct layers — a large outer layer with a smaller inner layer sitting on top. These distinctive craters were first documented in data returned from the Viking missions to Mars in the 1970s, and scientists have been trying ever since to figure out how the double-layer pattern forms.

A new study by Weiss and James W. Head, professor of geological science, suggests that DLEs are the result of impacts onto a surface that was covered by a layer of glacial ice tens of meters thick.

Read more of Kevin Stacey's article about Mars' craters.