The Metroid Prime Trilogy version of Metroid Prime uses the same credits-based system for unlocking extra game material as Metroid Prime 3 (so everything on this page only applies to the Wii version of Metroid Prime). All the bonus art galleries and the Fusion Suit are still available to purchase, although the original NES Metroid is only present in the original GameCube version.
Two types of credits exist for MP: orange and silver. Orange credits are all picked up from defeated bosses, while silver credits are gained as you collect artifacts (along with a few other tasks). See below for a complete list of how to go about collecting all the credits.
See the Secrets and Tips page for the list of all unlockable items, how to make them available for purchase and their credit cost.
A total of 10 orange credits can be collected. Each of the following bosses will grant you a single orange credit upon their defeat. Note that you can only collect these credits once per save file on any difficulty setting.
Most silver credits are awarded as each Chozo Artifact is collected. Filling up the Log Book will also grant a few other credits. A total of 16 can be gained in this game, tallying up to a grand total of 34 when combined with Metroid Prime 2's silver credits. See below for details.