Planet (The Macra Terror)

An Earth-like planet was the home of a human colony led by a Pilot. The planet was rocky, its foundation a type of salt that at depths generated gases over the years. It orbited a single sun and had either one or two moons.

Centuries after its colonisation, the colony was taken over by the Macra, who forced the colonists to mine the gas, deadly to humans but required by the Macra to breathe. The Second Doctor and his companions visited the planet and reversed the in and out flows of gas, killing the Macra and freeing the colonists. (TV: The Macra Terror)

Based on the Tenth Doctor's claim that the Macra were the "scourge" of galaxy M87, this planet may have been located in M87. (TV: Gridlock)

Behind the Scenes
The novelisation of The Macra Terror describes the planet having a single moon, while the animated reconstruction depicts two moons.