Ossus

Ossus is the third planet of the Adega system in the Auril sector, known to the galaxy long before 25,000 BBY. Under the rule of the ancient empire of Xim the world bore the name Idux. The Jedi came here from Tython, founded an academy, and made the planet the repository of all the wisdom they had accumulated — the Great Jedi Library was located here.

When the Jedi Knight Exar Kun turned to the dark side and unleashed the Great Sith War, he attacked Ossus, seeking the Sith secrets hidden there. In the course of these events the explosion of the Cron Cluster produced a shock wave that turned the once-flourishing world into an arid and poisonous wasteland.

The surviving descendants, including descendants of the Jedi, reverted to a primitive state and lost the memory of the Force, forming the Ysanna people. Later the planet was studied as an archaeological site, and after the war with extragalactic invaders an academy was reopened here, becoming for a time the center of the revived Order.