The First Mission to Byss was carried out by Jedi Rosh Penin in 14 ABY, for the New Jedi Order. Luke Skywalker assigned Rosh to investigate the remains of Byss, and determine whether the Disciples of Ragnos have been there.
Rosh was assigned to Byss, but never returned or made contact. After some time, Kyle Katarn decided to look for him on the planet's remains, and later with Jaden Korr and also to investigate since Penin's mission was never completed.
During that time, Rosh Penin fell to the dark side of the Force.
- Star Wars: Jedi Knight: Jedi Academy (Mentioned only)