First Mission to Byss

"Rosh, I'm sending you to the remains of the planet Byss. It's very remote, so I doubt the Cult has been there. Don't stay too long; the Imperial Remnant may still be operating in the area."

- Luke Skywalker to Rosh Penin.

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.

Prelude
After Luke Skywalker learned that Alora sliced into his records, which contained a list of places with strong a Force connection, he dispatched several Jedi to the locations mentioned in his diary.

The mission
Rosh was assigned to Byss, but never returned or made contact. After some time, Kyle Katarn and Jaden Korr decided they'd look for him on the planet, and also to investigate, since Penin's mission was never completed.

During that time, Rosh Penin fell to the Dark side of the Force.