Sense Sphere

The Sense Sphere was a rocky planet located in the Mutter's Spiral galaxy and was the homeworld of the Sensorites.

Profile
According to the Tenth Doctor, the Sense Sphere was located in the same star system as the Ood Sphere. (TV: Planet of the Ood) It had two suns, which meant the planet never had natural night-time. Its atmosphere was thick, which meant sound waves on the planet were increased in volume. The planet was also riddled with caves, which is where the Zilgans lived. (PROSE: The Monsters from Earth) It was also rich in molybdenum. (TV: The Sensorites)

The planet had yellow mountains with natural springs, as well as large aqueduct over which the Sensorite city was built. (TV: "Hidden Danger")

The Interior, literally inside the planet, was constantly in flux, constructed by the collective thoughts of the Sensorites. In here, gravity was context-dependent. (AUDIO: Sphere of Influence)

History
The Sensorites' development as a telepathic species was in large part influenced by their home planet, which had unique properties. In time, they developed a symbiotic relationship with the Sense Sphere, and drew much of their power from remaining together on the planet. (AUDIO: Sphere of Influence)

Early in its history, the First Doctor, Tony Barker and Amy Barker visited the Sense Sphere, where they angered the native Sensorites when the Doctor killed a Zilgan. However, they scared them off by shouting and escaped. (PROSE: The Monsters from Earth)

In the 28th century, the Sense Sphere was visited by two separate Earth expeditions. The first expedition discovered the existence of molybdenum on the planet. Two of the crew deserted and tried leaving in their spacecraft, but the Commander destroyed the ship before they could escape. The Commander and his two surviving crew went into hiding in the aqueducts of the Sensorite city and began poisoning the Sensorite's water supply with Atropa belladonna to wipe out the Sensorites and take the planet for themselves.

The second expedition was kept prisoner by the Sensorites to ensure their planet's future. The First Doctor eventually helped stop the survivors of the first expedition, and ensured that the Sense Sphere would not end up exploited by humans, as the native Sensorites would rather be left alone. During his encounter with the Sensorites, the Doctor encountered their leader, the First Elder, in a city on the Sense Sphere. (TV: The Sensorites)

The Sense Sphere finally capitulated to the Earth Empire in the 30th century at the end of the Wars of Acquisition. (PROSE: Original Sin)

During the Last Great Time War, three Daleks visited the Sense Sphere, claiming to need parts for their craft. Using their telepathic abilities, the Sensorites turned the Daleks against each other, unaware that they'd planted a Dalek mutant mixed with Sensorite DNA into the Interior. Unable to match the Sensorites' telepathy directly, the Daleks had bred the creature to increase the Sensorites' paranoia.

After the Daleks had seized control of a TARDIS, Susan Foreman suggested that the Time Lords seek out the Sensorites' aid to reconnect with the ship's telepathic circuits. As Ian Chesterton was recruited to join Susan, the War Council sent delegates throughout the Sense Sphere's history, establishing a relationship with Gallifrey as well as sending two Battle TARDISes to the Sense Sphere during the peace talks. As the Dalek parasite increased the Sensorties' paranoia, Susan and Ian descended into the Interior and defeated it, convincing the Sense Sphere to stand with Gallifrey in the Time War. (AUDIO: Sphere of Influence)