I just learned about this program called Spriter. It's free edition seems like a useful alternative for those of use who don't understand/don't own Anime Studio.

http://www.brashmonkey.com/index.htm

How big are the original source images? Certainly try to make them as small as possible (not size wise, but filesize wise). Each of the 35 objects aren't using a different picture are they?

You could put multiple rocks in one picture and then rotate it in the level editor so only one rock is visible, but that probably won't reduce the filesize very much.

You may end up having to only use two or three different rocks and repeating them in that screen. Or you could stick a few of them in your tileset. Then they'd be loaded when you get to the planet instead of on that screen.