Nice concept
Although this game looks simple, the physics involved give it a certain depth. Enough to keep me interested for a while at least. The only advice I could give is to make better graphics - a nice starfield background, interesting planets with craters and different colors, and a less monochrone comet. You could also add moving objects such as space debris (collidable) and other comets to add to game complexity. And most important: explain the goal of the game early on, it isn't that obvious. Oveall, good job with room for improvement.