Sontar

Sontar was the home planet of the Sontarans. Its name was included in the Sontaran battle chant, "Sontar, ha." (DW: The Sontaran Stratagem) 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)

In the parallel world where Donna Noble never met The Doctor, Captain Jack Harkness and Torchwood moved to stop the Sontaran fleet. Torchwood 3 was killed while Jack Harkness was transported to the Sontaran homeworld as he escaped. (DW: 'Turn Left'')

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