Trash

From the Super Mario Wiki
Mario blowing up Trash with Bob-ombs in the Battlerock Galaxy

Trash is an object in Super Mario Galaxy. It appears twice in the game, in the Battlerock Galaxy and the Dreadnought Galaxy. Trash can be destroyed by blowing it up with Bob-ombs. In both galaxies, the planet trash appears on is the "ammo department", and there is always one green Gearmo maintaining it. Both Gearmos complain that even though the ammunition department should be clean, people dump their garbage on the planet anyway. It is up to the player to clean the planet up by blowing up the trash under a time limit of third seconds. if successfully done, the Gearmo will award the player with a Power Star they "just found lying around." However, if the player fails to complete the challenge, all the trash will reappear suddenly. The player will have to start all over to beat the level. Yellow spots in both levels show optimal places to throw the Bob-ombs to do large damage to the trash.

In Super Mario Galaxy 2, trash is replaced with crates.