Atmosphere destroyer

An atmosphere destroyer was a Gallifreyan device capable of destroying a planet's atmosphere.

According to the Ninth Doctor, a Gallifreyan "high house" developed the device as part of their attempts to warp reality to their design during the Last Great Time War, likening it to their artillery. One survived the Time War and became the centre of a paradox involving the Doctor and Althea Bryce, with them eventually devising a way to break the loop to defuse it. (AUDIO: Her Own Bootstraps)