Cool idea for a game.
Very much fits the Jam theme. Art style is quite simple, but effective, although I don't really understand what the random giant and Pickaxe were doing inside an asteroid ;)
I liked the little touches you added like making the self destruction button a mechanic for clearing obstacles and having the asteroid rotate.
For improvements, a bit of music and some sfx would go a long way to adding to the feel of the game. I'm not sure how much more you're planning on working on this game, but it would be cool if you made it so that maps were made up of multiple asteroids, would add more depth to the game and more possibilities.
Overall, submission has lots of potential and places you could take it. Well done!