Aqua Magna

Aqua Magna, also known as the Endless Ocean Planet or the Great Sea, was the planet which Mata Nui crash-landed on as a result of the Great Cataclysm and a moon of Bara Magna.

History
Aqua Magna was originally the ocean of Spherus Magna. When the Shattering occurred, Aqua Magna broke loose and became a moon of Bara Magna.

When the Great Spirit, Mata Nui, completed his mission, he was returning to Bara Magna, when he fell into a coma because of a virus which the Brotherhood of Makuta had infected him with, and "crashed" on Aqua Magna. In the impact, part of the Mainland inside the Matoran Universe broke loose, punched out of Mata Nui's "chest" and subsequently rose up up the surface of Aqua Magna, forming an island which was later known as Voya Nui. After crash-landing, many islands of the Matoran Universe rose to the surface. Mata Nui's camouflage system also formed an island over his head, an island which was later known as the island of Mata Nui.

After the Toa Mahri destroyed the Stone Cord, Voya Nui sank back to it's original position. When the Toa Nuva awoke the great spirit, the Matoran Universe was reformed. Makuta Teridax located and possessed Mata Nui's "brain", a bank of machinery far beneath the surface of Metru Nui. When Teridax arose as the new Great Spirit on Aqua Magna, the Island of Mata Nui broke apart, destroying the landmass on the surface of the planet.

Teridax later left for Bara Magna to kill the great spirit. Later, during a battle on that planet, a gravity blast from Teridax pulled the moon back toward Bara Magna (unintentional), and they rejoined, along with Bota Magna. Right before the moon rejoined with Bara Magna, Mata Nui pushed Teridax, causing a chunk of Aqua Magna to smash the Great Spirit Robot's head, killing Teridax.

Trivia

 * "Aqua Magna" is Latin for "great water", or "great sea".