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Cool image time! The photo to the right, cropped and reduced to post here, was taken on December 7, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows what the MRO science team dubs “erosion of scalloped terrain” in the northern lowland plains of Mars.

The cracks invoke the polygon cracks one sees in mud as it dries. The circular feature suggests a buried crater whose shape is merely suggested because the cracks are conforming to the underground topography.

Are we looking at dried mud? Maybe, but more likely we are seeing a sheet of ice now sublimating away and cracking as it does so. If you look at the full photo you will see the cracked material also appears to drape itself over several nearby low ridges, something that seems more likely from ice than mud.

The overview map below also suggests this is a buried layer of ice.

The red dot marks the location of this picture. At 42 degrees north latitude, it is well within the region where scientists find ample evidence of ice and glaciers.

The real question then: Why is this ice cracking and eroding away? This far north ice seems to be found everywhere. In glacier country that ice almost always appears robust and thick. Only as you get close to 30 degrees north latitude does it begin to show sublimation features, with all evidence of ice disappearing as you approach the equator.

For this ice to be cracking suggests its protective layer of dust and debris has blown away, exposing the ice to the thin Martian atmosphere and thus allowing it to sublimate away. In fact, this image suggests the bigger mystery is that we don’t find more ice cracking and eroding as we see here. It seems astonishing that most of the glaciers found in the mid-latitudes are all so well protected by a thin layer of dust and debris. Yet it appears they are.