Asteroids, of course.
CnC

Very nice image, and amazing if you created that from scratch (which I think you didn't, did you?), especially the contrast. One area that I thought didn't look right would be the "outline" of the bottom left section of both asteroids. At some area's it's a dark outline, and at other's it's white (or light). I'd say try to keep them either all dark or no outline with some light depending on what effect you want to go for. Another area I noticed was at the asteroid closest to our perspective or largest in the picture, if you look closely at the top-ish area the light has a block where there is no light. And lastly, why is the asteroid's opacity lowered? (Where the 2 asteroids intersect you can see through the closest or largest asteroid).

Well, that's all I noticed.

I used a wax paper image to make the floor, a cement wall to make the wall, and 2 pictures of rocks to make an asteroid. Then I used that asteroid to make the other.

And the semi-opaque part of the asteroid was unintentional, but I kept it because it gives it a sort of impact look, ....I dunno I just like it.