Finally found time to play your game.
Let's come to the good parts first. The music and sound effects are very good. Also the foreground graphics are nice and the theme is clearly met. I love the dialog, especially that they are different when planets die in level 2.
Now a little bit about the negativ stuff. The background graphic (this galaxy cloud or what it should be) doesn't really fit with the foreground graphics. I guess these graphics where done by different people.
The control is clear, but selecting the correct planet is really hard, at least it was for me. Maybe you could give one of the violett planets a different color and also make the orbit in the color of the planet. This could help. Changing orbit speed is slow, but I guess this is wanted to increase the challenging aspect.
Some asteroid hits in level 2 are not registered. So a planet is hit, but doesn't take dmg. This should be a bug in the code somewhere.
But, overall a nice game. Don't be fooled by the big negative part, your rating is on the better side ;)
Just one thing at the end. You were a group of 4 who worked on this project. I don't know how much time you invested or how your experience in game design is, but for my sense, you could have done more. At the end it is just 2 levels with a quite basic mechanic.