Sontar

Sontar, sometimes called Sontara, was the home planet of the Kaveetch, who created the Sontaran clones during their war with the Rutans. The cloned Sontarans eventually became the planet's rulers.

Astronomical data
Sontar originally orbited its star like any other planet, but by 1609 it had been modified so that the star orbited Sontar, as a more "logical" pattern. (PROSE: The Empire of Glass)

Sontar generated a gravity level six times higher than Earth. (TV: The Last Sontaran) However, its gravity was not used to bolster the muscular fitness of Sontarans. The Sontarans actually had such strong physiques and muscles due to being created on Sontar's Moon, within its even higher gravity. (AUDIO: The First Sontarans)

Sontar had large octagonical structures on its surface. (WC: Captain Jack's Monster Files: Sontarans, COMIC: Pureblood) According to one account, Sontar appeared red when seen from space. (WC: Captain Jack's Monster Files: Sontarans) Another account showed it green, with vast metal structures covering whole continents. (COMIC: The Betrothal of Sontar)

Somewhere on the planet was the Hall of the Fallen and the Brave. (TV: The Last Sontaran) There were also desert areas, inhabited by Sontar sand shrews. (PROSE: The Sontaran Games)

History
At some point in their history, the Rutans attacked Sontar and it started a war between the Rutans and the Kaveetch. The Kaveetch were losing the war so they began to clone themselves to replenish the soldiers they lost. The clones eventually became the Sontarans and the Kaveetch were forced to leave Sontar. (AUDIO: The First Sontarans)

By the 17th century, the Sontarans had moved their star system so that their star orbited Sontar. (PROSE: The Empire of Glass)

The name Sontar was included in the Sontaran battle chant, "Sontar, ha." (TV: The Sontaran Stratagem) Circa 2009, the Sontarans chanted the name of their world to work up a battle-frenzy. (TV: The Poison Sky)

The Twelfth Doctor crashed on Sontar, upon gaining a new piece of the Orb of Fates. The Sontarans were defending it on a base, but "Lumpy", a Dalek working for the Doctor, retrieved it. (GAME: The Doctor and the Dalek)

In the 26th century, the Sontarans' enemies, the Rutans, destroyed Sontar with photonic bombs, leading to the creation of a new homeworld on Pandora, the planet around which the space station Pandora Spindle orbited. (COMIC: Pureblood)

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