I've tried running around randomly as an asteroid and a planet, and I've also just tried going on and on and on for miles across the universe, but I haven't been able to unlock the "Get Lost" achievement in the steam release of Solar 2.
It's from the last part of the "Heist" mission series as a star. You need to leave the trap death line of stars that are spawning. It doesn't win the mission but it does get the achievement. I did it by loading my largest star system and just plowing my way through the killer flying stars.