More planets give more resources for stronger Empire. Send this unit on any unoccupied planet with order "Colonization", and if the level of Colonization technology more than the number of your planets, you will get one more planet when your unit reach the free planet. By the same way you can colonize pirates station. You can also colonize free or occupied asteroids. It is a battle when you colonize asteroid. Win this battle for successful colonization. You cannot activate vacation mode during 24 hours after colonization of asteroid. You can abandon this asteroid for urgent leave to the vacation mode.