Dunes + Craters = Mars

A Piece of Mars: How do you tell when a planetary landscape shows Mars, instead of Mercury or the Moon or Europa? The easiest way to tell is to look for both craters and dunes, like what’s shown here in this 640×360 m (0.4×0.22 mi) scene. Not all martian landscapes have either feature, and there are some other worlds that do have both (Earth, Titan, maybe Pluto, and probably Venus but we need better data…), but it’s a pretty good bet that if you see both features together, you’re looking at Mars. Anyway, in this lovely view, the dark gray terrain (you’ll see boulders if you look closely enough!) is being eroded away slowly, revealing a much older, brighter surface beneath it. Unfortunately for those who would study ancient terrains on Mars, much of that older, lower surface is covered in dunes. But I like the dunes – they give us information about surface erosion rates and wind patterns. One person’s signal is another person’s noise. (HiRISE ESP_047762_1585, NASA/JPL/Univ. of Arizona)