Click for full image.
Cool image time! The picture to the right, rotated, cropped, and reduced to post here, was taken on September 3, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). The focus of the image for the MRO science team were the wedding cake layers inside the largest crater. These layers suggest glacial ice, with the layers suggesting multiple cycles of glacial ebb and flow. Since the crater is at 43 degrees north latitude, and sits in the chaos region dubbed Protonilus Mensae, smack dab in the center of what I call Mars’ glacier country, this conclusion makes perfect sense.
To my eye, however, the most interesting feature of this photo are the many distorted craters. The overview map below shows the picture’s location, as well as several nearby very large impact craters which might have caused many secondary impacts, including the many craters at this location.
The red dot marks the location of today’s cool image. The three mensae regions cover most of Mars’ northern glacier country.
Why are the craters distorted? Research has shown that even at impact they would have been circular, even if the impact has been an oblique one.
My guess is that the solution lies underground, which at this location probably has a somewhat thick near-surface ice layer. When the impact occurred, much of the ejecta that formed the crater rim’s was probably frozen ice. The heat of impact would have vaporized a great deal of that ice, but enough would have simply melted and then quickly refroze. In that melt-freeze process it is very likely that the crater rims would have ended up distorted.
Furthermore, later impacts on top of older craters would have distorted those older craters further, as it appears happened to the craters to the east of the largest. In the overview map the large craters to the west, 147-mile wide Lyot Crater and 86-mile-wide Moreux Crater, would have produced many secondaries at two different times, thus resulting in the overlay and melted effect seen here.
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