Talk about it here.
Tranquility was a planet visited by the Tenth Doctor and Heather McCrimmon. However, the Doctor was shocked to find the planet in ruins. Joining the Bereft on their journey to the Eternity Canyon, the Doctor and Heather encountered T.R.O.L, the robotic creation of the Bereft's warlike ancestors. The Doctor travelled on T.R.O.L to the planet's crust and found a military bunker. He discovered an ancient bomb had caused tremendous damage to Tranquility. The Doctor resettled the planet's defence shield so that the Bereft could escape before the bomb exploded and destroyed Tranquility. After saving the population, the Doctor and Heather watched the destruction of Tranquility from space, hopeful that Tranquility would be reborn in a thousand years. (COMIC: T.R.O.L)