Greetings friends,
Lately I found this game, which would interest most of you space lovers. It's name is Universe Sandbox
It can do from asteroids hitting Earth, or stability of the solar system, up to entire galaxies, galaxy collisions (like Andromeda with our Milky Way) and black holes. It also has many fun modes/scenarios, where you shoot asteroids at Earth and see how it react, and dozens more. Also everything in the universe is EDITABLE, so you can change a planet's (sun or anything else's ) mass, speed, size, temperature, density, etc. So you can make out everything you can imagine in here, even spawning Halo rings (from Halo), dices, footballs and stuff... make them collide, etc.
Some videos:
You can buy it, play the trial (30 mins), or using your imagination (other ways), you're on the internet
Have fun and,
- Enjoy !
~~Mike