Green Star

Green Power Stars are green-colored Power Stars that can be found in Super Mario Galaxy. Only three Green Power Stars are known to exist, all of which are hidden away in certain galaxies. Collecting all three of them will grant Mario access to the three Trial Galaxies, those being the Rolling Gizmo Galaxy, the Loopdeeswoop Galaxy, and the Bubble Blast Galaxy. Green Lumas will grow up to turn into Green Power Stars.

One Green Power Star is hidden in the Buoy Base Galaxy, another is hidden in the Dusty Dune Galaxy, and the last one is eventually discovered by Luigi in the Battlerock Galaxy.

Trivia

 * Even though only three Green Power Stars are recovered in the game, a total of seven Green Lumas can be found on the Comet Observatory and the Planet of Trials.