Neat idea. It took me a while to figure out that you could jump to other planets, but I really like how there were unique powerups tied to each one. Since I see it mentioned in several comments: my suggestion for the controls would be to not have a dedicated fire button, but use the arrows for firing. Since you already have A/D mapped for movement, you could use the arrows to shoot left or right (similar to how a twin stick shooter might work). Keep it up!