Hm, thats interesting. In US2, there is a method for easily spawning hurtling bodies from your screen at unsuspecting planets.
Pressing 1 spawns an asteroid of determined size;
Pressing 2 spawns Mimas;
Pressing 3 spawns Ceres;
Pressing 4 spawns The Moon;
Pressing 4 spawns Earth;
And so on until you end up launching Jupiters and stars by the time you get to 7 or something. Therefore, you might of pressed some numbers while you were in another window and US2 thought you wanted to spawn something. Does the asteroid say Asteroid 80-something metres? Or is it 40- something metres? Sorry I cant remember meh Ubox wont start.