How do I move the player in a circular motion?

I need help making my player rotate left or right in a circular motion around an object. When I press the down arrow key, the player should be able to move down a level or closer to the planet and if I press the up key, the player should move up a level or further from the planet.

I also would like to know if it's possible if a object can destroy itself and another (same) object at the same time?

For example comet(frame 1) on collision with comet(frame 0) = destroy comet (both)

Here is a link to the capx and example illustration:

https://www.dropbox.com/sh/jers1bso4z0e ... z4qXC201ba