I think this has a lot of potential if you tweak some things a little. Reminds me a lot of Gravitee, an online space golf game I really like. Obviously this isn't the defacto way to fix it, but I have two suggestions:

1. I agree with JafCraze: the planets shouldn't have gravity until you place them. If you're trying to play properly, it's really easy to have that throw you off-course, and it's really easy to abuse if you want to: since the planets don't hurt you, you can just let the ship hug them forever and earn points (I could only get maybe 30 points normally, but got about 300 this way).
2. I don't know if planets should hurt you? I'm not as sure about this one, but I think it's too easy to underestimate the gravity's strength and get hurt that way. I'm thinking that either the planets should just knock your ship out of control towards asteroids, or that it should be easier to tell where the ship will go, maybe with a prediction line or if it just moves slower.

I really appreciate the amount of polish with the sprites and music in this one.

Pretty hard to control but I think that's the point :D

I don't think celestial bodies should affect the ship before they are placed

My final score (while playing it my way :P)