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.

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 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 floated on the surface of Aqua Magna, forming an island which was later known as Voya Nui. Mata Nui's camouflage system also created 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, leaving the Island of Mata Nui the only known landmass on the planet.

When the Toa Nuva awoke the great spirit, 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 was broken, destroying the landmass on the surface of the planet.

Makuta Teridax has since left for Bara Magna. Later, during a battle on that planet, a gravity blast from Teridax pulled the moon back toward Bara Magna, and they rejoined. Makuta had told Mata Nui that his gravity blast could destroy Bara Magna therofore his gravity blast turned the moon into chunks. One of the chunks hit Makuta in the head killing him.

Trivia

 * "Aqua Magna" is Latin for "great water", or "great sea".
 * A blue object of Spherus Magna struck Teridax on the back of the head as it headed towards Spherus Magna, killing him. It is unknown if this was Aqua Magna or not because it was quite small.