How did you even come up with this idea ?? XD
I played it on HTML, it was hard but I had a good laugh of panic when I thought it was a good idea to throw the comet away quickly, turning it into a high speed uncontrollable missile.
I like that the planets can change texture for each try, would be even better if they look more like earth or like a habitable planet.
There are times when the planet leave the screen entirely, while the do float back after a few seconds, I think it is important that at least half of the planet should be visible at all time.
Overall, it's a very original idea. nice work !