Delta III

'Delta III was the third moon of Delta Magna and refuge for the Swampies, natives of Delta Magna forced to relocate there by Humans who had colonized their original homeworld.

This moon was small, having weak gravity and a poor atmosphere, Humans had released Giant Squid on the moon to impress the Swampies. The moon was covered in swamps and bogs and was rich in methane. When Humans discovered this second feature, they set up refineries and attempted to exterminate the Swampies, a move disapproved of by such groups humanitarian groups as the Sons of Earth.

The Doctor and Romana found the second segment of the Key to Time there, in the form of the Swampy's god Kroll. (DW: The Power of Kroll)