Eggman's Chaos Energy Cannon is a vast energy weapon used by Dr. Eggman in the opening cutscene of Sonic Unleashed. Heavily guarded by the Eggman Fleet, it was built by the mad scientist to release Dark Gaia as described in the Gaia Manuscripts.
The size of a large space station, this orbital weapons platform leeches power out of Super Sonic and the Chaos Emeralds, channeling it into a giant laser beam that is fired into the ocean of Sonic's world. The beam fractures the world into multiple continent-sized pieces, releasing an immature Dark Gaia from the world's core. Feedback from Dark Gaia via the weapon seems to be what turns Sonic into Sonic the Werehog.
Professor Pickle gives the cannon its name in his hint The shattered planet.
The Eggman Fleet guards the cannon in the opening
Dark Gaia minions: