This is fantastic.
Everything about this demo is gorgeous.The art gives me good space vibes love it, and that music is so smooth,I didn't think game boy music could be so smooth.
Was there a ship dock in the asteroid belt? If there was I couldn't find it. The arrows wasn't very helpful in that area, and I got frustrated so I decided to move on.
Also you should add some indicator to show where you can exit the screen. Found myself rubbing my ship against the right space border until I found the small part that lets me leave.
9/10 Perfect other then minor issues.
All and all I don't think I'd mind having a space harvest moon. :3