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.

Fiction

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. The Covenant of Primus

Animated cartoon continuity

Neutronia was a destroyed planet that was part of both the Autobot Commonwealth and the Quintesson Pan Galactic Co-Prosperity Sphere in the Milky Way. The Complete AllSpark Almanac

Ask Vector Prime

In Primax 489.0 Zeta, Neutronia was destroyed by a rampaging Majin Zarak. Ask Vector Prime, 2015/07/10