Neutronia

Neutronia was one of the Cybertronian colonies during the Golden Age. It was one of the many planets to be hit by the Rust Plague.

Transformers: The Covenant of Primus
The Neutronia colonists fled into space when the Rust Plague struck their planet. Led by Mercury, they discovered the Transformation Cog of Amalgamous Prime near a black hole and eventually became the Mutacons because of long-term exposure to its power. After the Rust Plague ended, the Mutacons returned to Neutronia, stocked up heavily on energon, then departed into space again in the hopes of finding Amalgamous so they could return his device.