Ah here is the game description link. It was indeed called Planet's Edge by New World Computing and released in 1991
It was actually made by the same creators of Might and Magic. The premise is that Earth disappeared after an alien ship blasts it.
http://www.mobygames.com/game/sheet/p,2/gameId,765/
Amazingly it was written for DOS
I wish someone would come out with another game like this. I had a lot of fun.