Click for original image.

In looking through new images from Mars Reconnaissance Orbiter (MRO), I sometimes stumble some very strange things, with today’s cool image an example. The picture to the right, rotated, cropped, and reduced to post here, was taken on May 7, 2023 by MRO’s high resolution camera, and shows the western half of a two-mile-wide crater with a very weird rim, almost as if a person had decided he wanted to reshape it with a filigree pattern.

Though only two-miles wide, this crater actually has been named Johnstown. I suspect this is because of its strange rim, prompting a research effort and the need to provide it a name. Why the rim has this repeating pattern of gaps, however, is beyond my pay grade to explain, and I have been unable to track down any research papers about it. The nearby surrounding surface suggests vaguely the possibility that this is a caldera, not an impact crater, but even so why would the rim of the caldera have these regular breaks?

The white dot marks the location of the crater, inside larger 50-mile-wide Morella Crater. The inset, created from a mosaic of MRO context camera pictures, shows the rest of Johnstown Crater at lower resolution.

The south rim of Morella is itself cut by Ganges Cavus, a 25-mile-wide basin 15,000 feet deep. With no outlets or drainage features, Ganges Cavus looks very much like a giant sinkhole, created when the surface slumped down into a void below. There are a number of these titanic sinkholes surrounding Valles Marineris. Similarly, the fissures in Noctis Labyrinthus to the west, the likely source of this grand canyon, also appear to be made of sinkholes.

Taken together, these sinks strongly suggest that Valles Marineris was first created by an underground flow that created a void, which then became a sink, and finally become the canyon we see now.