Antilla

Antilla is an ancient ringed planet which was the site of an early Autobot colonization effort. This colony developed a very advanced, peaceful civilization, but was eventually wiped out by the deadly plague known as Cosmic Rust.

Cartoon canon
The Thirteenth Legion of Autobots, fleeing the wars of Cybertron, landed on Antilla. There, they founded a thriving colony. Eventually, however, they were all dead due to the malignant Cosmic Rust.