Click for original image.

Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on October 4, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). Labeled a “terrain sample” by the science team, it was likely shot not as part of any specific research project but to fill a gap in the schedule so as to maintain the camera’s proper temperature. When the camera team has to do this they try to pick targets that are of some interest. Usually they succeed, considering the enormous gaps we presently have of Mars’ geological history.

This picture is no different. It shows a land of buttes and mesas, all ranging from 20 to 200 feet high, surrounded by canyons filled with ripple dunes of Martian dust. If you look at the floor of those canyons closely, you will notice that where there are no ripple dunes the ground is slightly higher and smooth. It is as if that ground was a kind of sandstone that was eroded away by wind into sand, which then formed the dunes.

The white dot on the overview map to the right marks this location, on the edge of one large section of the Medusae Fossae Formation, Mars’ largest volcanic ash field, larger than the subcontinent of India and believed by some scientists to be the source of most of the red planet’s dust. In the inset, created from a global mosaic of MRO’s context camera images, the white rectangle indicates the area covered by the photograph above.

Being on the edge of Medusa this region is the transition zone from deep volcanic ash and lava. What seems to be happening here is that — like the mesas of Monument Valley in the southwest U.S. — the thick many-layered volcanic ash of Medusae is being eroded by the thin Martian atmosphere, leaving behind these buttes. As you move to the west there is more ash, filling the canyons. As you move east the buttes slowly vanish as the ash disappears, and the ground drops to the base level of hardened lava.