According to the Tenth Doctor, the Sense Sphere was located in the same star system as the Ood Sphere. (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. (The Monsters from Earth) It was also rich in molybdenum. (The Sensorites)
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. (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 they left them alone. (The Sensorites)
The Sense Sphere finally capitulated to the Earth Empire in the 30th century at the end of the Wars of Acquisition. (Original Sin)
When remembering his travels with the First Doctor, one of the things Ian Chesterton recalled was this planet. (Hunters of the Burning Stone)