Sontar

Sontar was the home planet of the Sontarans.

History
The name Sontar was included in the Sontaran battle chant, "Sontar, ha." (DW: The Sontaran Stratagem) Sontar was a reddish planet with gravity six times higher than that of Earth's; this is said to be how the Sontarans develop such strong physiques and muscles. (Captain Jack's Monster Files: Sontarans) (DW: The Two Doctors)

Circa 2009, the Sontarans chanted the name of their world to work up a battle-frenzy. (DW: The Poison Sky)

Circa the 25th or 26th century, the Sontarans' enemies, the Rutans destroyed Sontar with photonic bombs, leading to the dispersal of Sontaran troops across their home galaxy of Mutter's Spiral. (DWM: Pureblood)

At a time when a Pureblood Sontaran is seen running a mining ship, a planet of Sontar is shown; it was coloured green, with vast metal structures covering whole continents. This may be a new planet of Sontar.(DWM: The Betrothal of Sontar)

Donna's World
In the parallel world where Donna Noble never met the Doctor, Captain Jack Harkness and Torchwood Three moved to stop the Sontaran fleet. The Torchwood team were killed while Jack Harkness was transported to Sontar. (DW: Turn Left)

Other information
The supreme military commander and founder of the Sontaran Empire, General Sontar, had the same name as the planet.