Surface features common in the northern and southern midlatitudes of Mars and known as lobate debris aprons and lineated valley fill are believed to have formed either as debris flows mobilized by pore ice or as debris-covered glaciers.
To learn more, Kress and Head define and analyze ring mold craters, which are abundant on debris aprons and lineated valley fill but not seen in surrounding terrain. Ring mold craters are concentric crater forms named for their similarity to the cooking implement, in contrast to the bowl-shaped craters that are common at such small sizes (hundreds of meters (hundreds to thousands of feet) in diameter).
On the basis of similarities in shape of ring mold craters to laboratory impact craters in ice and of the physics of impact cratering into pure ice, the authors interpret ring mold craters to result from projectiles hitting relatively pure ice below a thin debris layer.
These results support the hypothesis that lobate debris aprons and lineated valley fill are debris-covered glaciers and that many hundreds of meters of ice remain in these deposits today on Mars.
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