Click for full image.

In the past four years I have posted hundreds of cool images taken by the orbiters circling Mars. From those images I have been able to slowly gather and pass on to my readers some of the solid knowledge that scientists are gaining now about the Red Planet.

The image to the right illustrates best why one must never make any quick assumptions about the features you see in these photos. Taken on November 28, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), it shows a small crater that appears partly filled with material. On its walls can be seen many slope streaks, a still unexplained feature unique to Mars that is not caused by rock or debris avalanches.

As for the material inside the crater, based on the majority of Martian images showing similar craters, the first assumption one might make is that this material is some form of eroding glacial material.

That first assumption however would simply be wrong. Glacial material found in Martian craters is routinely found in the mid-latitude bands between 30 and 60 degrees. This crater is sits almost exactly on the equator of Mars, where scientists have found no evidence of any glacial material or near-surface ice. In the equatorial regions the surface of Mars is essentially dry.

So what is that patch of material? As always, location is all.

The crater sits, as indicated by the white cross, on the edge of the giant volcanic ash deposit dubbed the Medusae Fossae Formation. The deposit in the crater’s floor is thus almost certainly trapped volcanic ash from Medusae.

If you click on the picture to see the full resolution image and zoom in close, you will see that in detail this patch does not really have the soft appearance of sublimating ice. It appears harder, like the slickrock sandstone of the American southwest that was once sand dunes that over time hardened into rock, but is now easily eroded by wind.