From the Super Mario Wiki
A Silver Star in a
Star Sphere.
A
Star Sphere is a clear ball in
Super Mario 64 DS. If a player receives five
Silver Stars, or presses a
Star Switch, then a
Power Star will appear in the ball. (If it was a Star Switch, it will only last for 10 seconds.) When the Star Sphere is touched, it will break, allowing the player to get access to a regular Power Star or a
Secret Star.
