Diobath

Diobath was an experimental alien planet of various environments created by a company called Sierra Logistica. Over time its rodent-like inhabitants (part of the original experiment) evolved into peaceful creatures with their initial marked on their foreheads. They sheltered in the underground systems. Over many centuries, after the company ceased trading, the planet’s systems began to break down and decay. Off-worlders like the Gorolox waited to plunder the planet until the bio-dome began to collapse and chunks of the planet's ‘sky’ fell to the ground.

The Doctor repaired the underground systems (used as a safe house by inhabitants like Mersal and Kilo). The invading Goroloxes left, fearing that the planet was being protected by their sworn enemies. (DWA: The Sky is Falling!)