On the floors of young craters of the Moon, smoothly rounded domes are visible in some spots. Lalande crater has 4 of them, each around 200 m across.

domes on floor of Lalande crater

Lalande crater floor in the evening

Here are less regular ones on the floor of Copernicus crater. The most pronounced one, in the middle, is 500 m across.

domes on floor of Copernicus crater

The ones in Lalande in particular are quite round and regular, and make me think of bubbles on the surface of a thick liquid. I have looked for material on such domes without luck. I asked Paul Spudis if they could be hollow when he appeared on a recent Space Show episode , and he said yes. (Relevant portion starts at 36:45, with a discussion of impact melts, and then gets into the domes.) He indicated we can't know but it is possible. I wish I'd followed up with more questions, but I thought I'd be taking too much time away from other people with questions, and left it. I won't make that mistake again.

Can anything more specific be said about such domes, for instance based on similar dome morphology on the Earth or other bodies? If they are hollow, would it be the case of a hollow disk at the top of them, or a whole spherical bubble deep inside? If they are solid, then what would be the nature of their development?

  • $\begingroup$ Did you ever find out more about this? $\endgroup$ – called2voyage Jul 19 '18 at 19:51
  • $\begingroup$ @called2voyage No, i haven't. I updated a broken link to the show where it was discussed. Since it seems there isn't a way to get a concrete answer because not enough is known, I let it go. IIRC, Spudis said another possibility is the domes are due to a lighter molten material welling up under a skin of hardened material, which could mean they are solid. $\endgroup$ – kim holder Jul 19 '18 at 20:01
  • $\begingroup$ Ok, I considered putting a bounty on this, but it sounds like it's pretty unanswerable for the time being. $\endgroup$ – called2voyage Jul 19 '18 at 20:02
  • $\begingroup$ @called2voyage I found the part of the interview where he talked about it and put the timestamp in the question. He didn't get into alternate explanations on the show. I emailed him about it after that and he was kind enough to respond. That was when he mentioned he actually doubted there were voids. Perhaps he'd thought about it more later. What he said is that they could be mounds of ejecta that seem rounded because of how molten material only partly drained from them. Perhaps I heard the thinner liquid hypothesis elsewhere. $\endgroup$ – kim holder Jul 19 '18 at 20:42
  • $\begingroup$ Terrestrial meteorite impact craters get such central features too, and should be more accessible; maybe that would be worth researching? $\endgroup$ – SF. Jul 19 '18 at 21:23

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