Looks like a few smaller hunks smacked down just to the right it, in the pic as posted.
Yeah.
regarding the erosion, the plain is probably really hard basalt, so erosion would take a while. The various bits of crap that lay there as a consequence of the disintegration of the impactor (and the rock that had been where the crater is now) washed away long ago, no doubt.
speaking of doublet impact craters...
Red Planet's Ancient Equator Located
Scientific American (online) | April 20, 2005 | Sarah Graham
Posted on 04/24/2005 8:18:25 PM PDT by SunkenCiv
http://www.freerepublic.com/focus/f-chat/1390424/posts