Planet of Trials

The Planet of Trials.

The Planet of Trials is a small planet orbiting the Comet Observatory in Super Mario Galaxy. The planet can only be accessed once the three Green Power Stars have been recovered. Once they are collected, the Green Lumas will activate a Launch Star which will allow Mario to travel to the planet.

The planet then serves as the hub for Mario to enter the three Trial Galaxies: the Rolling Gizmo Galaxy, the Bubble Blast Galaxy, and the Loopdeeswoop Galaxy. After 120 Power Stars have been collected with both Mario and Luigi, a fourth Green Luma will appear on the planet and grant access to the Grand Finale Galaxy.

Trivia

• It should be noted that the launch star is indeed the only way to reach the planet. If you attempt to fly to the planet, Mario will stop flying half way through, and the Toad Brigade claims that their ship is unable to actually touch the planet. It's possible that the planet has the power to keep people from entering through any way but using the launch star.