Click for original image.

The nature of today’s cool image suggests both ancient and more recent geological activity, each coming from entirely different sources but both helping to shape the alien Martian surface.

The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on March 13, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows what the science team has labeled an “elongated depression,” sitting in the middle of a relatively flat but very rough stippled circular plain about 60 miles in diameter. An MRO context camera picture, taken on February 19, 2012, covered the central strip of this plain, and shows that its surface is equally rough and stippled everywhere, with only a few craters and one or two slight changes in elevation.

So, how does this feature tell us both about the ancient and recent geological history of this spot on Mars?

The black dot in the center of the inset on the overview map to the right shows us the depression’s location in the southern cratered highlands of Mars. As cratered as the highlands are, however, this flat plain is mostly devoid of craters, suggesting it might be an ancient flood lava plain. This depression appears to have been the main outlet vent for that lava, as the highest thin lava layers appear centered on it.

Because this particular location is so smooth, it suggests the lava event likely occurred after the heavy bombardment period in the early solar system several billion years ago that created most of the craters on Mars, the Moon, and Mercury, so that those craters were covered and filled.

That lava event however was still likely more than a billion years ago, and since then a lot of atmospheric erosion has taken place to roughen the lava’s surface. You can even see what appear to be a handful of pedestal craters along the north edge of the depression, craters that had been filled with lava and hidden, but are now revealed by subsequent erosion.

This is one theory. The location is also located at 34 degrees south latitude, in the mid latitude bands where orbital images find much evidence of near surface ice. It is also possible the rough surface is the result of ice sublimation processes. The ice might be sitting on ancient lava, but the surface is being shaped by the ice, not the lava.