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 inhabited the Sontar system. (COMIC: Supremacy of the Cybermen)

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, WC: ) 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: , COMIC: Pureblood) According to one account, Sontar appeared red when seen from space. (WC: ) 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)

The Thirteenth Doctor bought a Sontaran Frosted Boom Cake at a bakery on Sontar. (PROSE: Dr. Thirteenth)

Donna's world
In a parallel universe where Donna Noble never met the Tenth Doctor, Captain Jack Harkness and Torchwood Three stopped the Tenth Sontaran Battle Fleet's attempt to tranform Earth into a Sontaran cloning world. The Torchwood team were killed and Jack Harkness was transported to Sontar. (TV: Turn Left)

Alternate timeline
In an alternate timeline where the Cybermen used Time Lord resources to conquer all of history, by the 24th century, the Cybermen had destroyed nearly the entire Sontaran Empire and successfully driven the last surviving Sontarans back to Sontar; the Cybermen sought to gain control of the planet's cloning factories to produce an endless supply of Mondasians for cyber-conversion, with the Tenth Doctor speculating that the Cybermen would then mobilise Sontar via void drives to reproduce Cybermen infinitely across the universe. The Sontaran-Prime oversaw the capture of the Tenth Doctor for his assistance in the Sontarans' final battle with the Cybermen. After the Imperial Flagship of the Last Great Sontaran War Fleet crashed on Sontar due to an attack from the Cybermen, the Sontarans marched into battle against the Cybermen, the latter of whom descended onto Sontar via Gallifreyan portal technology. When a CyberKing caused a Sontaran scout ship piloted by Gabby Gonzalez and Cindy Wu to crash, the Doctor crashed his own scout ship into the CyberKing and took control of it, obliterating most of the Cybermen and destroying the other two CyberKings; despite this, a Cyber-Ark descended on Sontar and commenced planetary conversion, seeding the entire planet with Cyber-Technology.

Ultimately, this timeline was erased when, at the end of the universe, the Twelfth Doctor and a betrayed Rassilon used the Eye of Harmony on Gallifrey to regenerate the universe and restore the original timeline. (COMIC: Supremacy of the Cybermen)

Sontar