Deimos

Deimos was a moon of Mars.

The Ice Warriors fled to Deimos after radiation killed the soil of their home planet, Mars, putting themselves in suspended animation inside some catacombs for — according to the Eighth Doctor — "many millions of years". (AUDIO: Deimos)

In the 21st century, the Deindum tried to make Deimos and Phobos leave Mars' orbit. Merlin sent Excalibur to Winifred Bambera and Ancelyn in order for them to use the sword to prevent the Deindum's plan from suceeding. (PROSE: Excalibur of Mars)

A moonbase was set up on Deimos intending to terraform Mars and make it habitable for humans. However, the Great Recession, along with insufficient funding for artificial suns to heat the planet, meant the terraforming project was abandoned. In the 23rd century, a group of Ice Warriors (AUDIO: Deimos) that was prematurely awakened from their catacombs by the Monk (AUDIO: The Resurrection of Mars) attacked Deimos Moonbase, intending to use the still-functioning atmospheric re-ioniser to make Mars habitable to Martians, but killing the thousands of human colonists in doing so.

The base was evacuated, (AUDIO: Deimos) but an artificial gravity eddy was used to bring the passenger rocket back down to Deimos. After the Doctor was forced to repair the re-ioniser when the Ice Warriors threatened the craft, the Ice Warriors destroyed it anyway by testing the re-ioniser, killing the 600 passengers and crew.

The Doctor, unable to reverse the effects of the device once it had started altering Mars' atmosphere, brought the re-ioniser "to a very sudden halt with a very loud bang" by reducing a critical feedback in the ionisation beam. At the last minute, the Doctor also made the process alter Mars into an Earth-like atmosphere rather than that of the Mars of long before. The feedback in the beam lit up the atmosphere of the base, setting the entire moon on fire and turning it into an artificial sun that heated Mars. The Doctor noted that this event was part of the Web of Time. (AUDIO: The Resurrection of Mars)