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Cool image time! The photo to the right, rotated, cropped, and reduced to post here, was taken on October 2, 2022 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a cluster of craters filled with ripple dunes.

The color strip tells us something [pdf] about the surface materials here. The reddish-orange in the craters is thought to be dust. The greenish terrain above the craters is likely coarse rock or bedrock, covered with a veneer of dust.

There is no ice here, just dust that over time has become trapped in the craters and cannot escape. And though there is also dust on the surrounding terrain, there is not that much. The craters themselves are likely very ancient, based on their shape and the eroded condition of their rims.

The black cross in the center of the map to the right marks the location of this picture, in the southern cratered highlands in the Martian dry equatorial regions.

Though there is evidence of past water or ice near the equator in other places on Mars, the terrain here suggests little such activity, for a very long time. In some ways this surface more resembles the Moon than Mars, hardly changed since the period of heavy bombardment in the solar system’s first billion years, when the planets were first forming.

The dust inside the craters tells us however that wind erosion definitely occurs here, whether or not water or ice was ever a factor. Over the eons, the thin Martian wind blows dust across these craters, smoothing out their rims while dropping some dust inside them, where that dust remains trapped pretty much forever.