Irregular Circular Depressions?

Dear Dialog,

I have come across something weird in my research. I am not sure what it is or how to describe it exactly but let me try. A little while ago I noticed some circular-ish depressions around the rim of Yorktown Crater and didn’t think too much of it. I was mostly exasperated that the melt at this particular crater was not clear according to the guidelines I have set for myself. There wasn’t any pitting or flow features but there were a couple of flat looking areas. Check them out in the carousel below, the first one is of Yorktown.

I asked Livio what he thought they could be and he said “I don’t know“ followed up shortly by “…they might be craters“. I was incredulous from the start. These things only appeared proximal to the rim of Yorktown. It would have to be a statistically unlikely chance that these features were impact craters that merely happened around the rim in the flat areas (or at least what I think are the flat areas. I have yet to make a DTM of the site but it is on my to do list). They are so irregular that I am not sure I’ve seen craters with that type of shape, especially in clusters. Craters tend to look fairly circular or elliptical or even square sometimes, but never this irregular. Binary craters often look like they are two cells undergoing mitosis. And craters that form on the sides of slopes can look elliptical or smushed like a ball in the middle of being struck with a bat. Some secondary craters can look irregular but not quite in the same manner. To add to this, there aren’t any signs of ejecta lines. Nor do these display the usual signs of pitting within melt.

I have started keeping track of the features in my my work. They seem to only appear next to the rim of the crater in seemingly flat areas. There may be signs of elevated ridges of some sort, but a DTM is needed to confirm the shape and structure. Another odd thing to note is I think most of these features appear around craters in Acidalia Planitia, which is about mid-latitude on Mars, and so far I have only found them on the north side of their parent craters. This could possibly indicate a periglacial driven mechanism as that can often produce odd looking features, such as brain terrain, but again, I haven’t seen anything similar in my work so far to these particular shapes. I am optimistic for a volatile-melt driven mechanism and could potentially be another indicator as to where melt exists. But to be fair, my research mostly focuses on melt around craters and I am usually looking at the areas near the rim of craters so maybe it is a product of selection bias. If they were volatile driven, I would need more confirmation in other ways as I don’t know everything about how volatiles can interact with impact melt.

Hopefully I can get to the bottom of this soon!

-W