The junior novelization of Star Wars: The Rise of Skywalker reveals the history of the Sith planet Exegol. The final movie in the sequel trilogy is essentially the story of Emperor Palpatine's ultimate defeat. The Dark Lord of the Sith had been overthrown in Return of the Jedi, and apparently killed, but his spirit had fled into a clone body and thus was able to return.
Far from extinct, the Sith had flourished on their last redoubt, the planet Exegol. Palpatine was resurrected on Exegol, hidden from the galaxy in the depths of the Unknown Regions, safe behind a labyrinth of solar storms, rogue magnetospheres, black holes, gravity wells, and things far stranger. There, he had prepared his Final Order, a fleet of Star Destroyers armed with planet-smashing weapons.
The Star Wars: The Rise of Skywalker junior novelization briefly fleshes out Exegol's history, revealing how it had become a Sith stronghold. In one key scene, Rey flicks through the pages of the Aionomica - one of the old Jedi texts - and reads about the difference between the Jedi and the Sith:
"The Prime is One, but the Jedi are Many. The Sith were Many but often emerge Ruled by Two. The Seeds of the Jedi have been Sown throughout the Galaxy, on Ossus, Jedha, Xenxiar, and Others. The Sith have no Seeds, since what they Bury does not Grow. They are the Despoilers of Worlds, and have Laid to Waste once Fertile Habitats such as Korriban, Ziost, Ixigul, Asog, and Others."
This is a Jedi text, of course, which means it can hardly be said to be impartial. Still, assuming the Jedi historian who recorded it was even remotely accurate, Exegol - known by the ancient name Ixigul, as in early drafts of the film's script - was once a fertile planet. The Sith Empire had discovered Exegol, and no doubt saw the potential of a last, impregnable stronghold that only they could access by means of the Wayfinder. If this really was once a place rich in life, then the Sith certainly have 'despoiled' it, given the Exegol of Star Wars: The Rise of Skywalker is barren and ravaged by the dark side of the Force.
The junior novelization also names a couple of key Sith worlds from the old Expanded Universe, helping to absorb them into the canon. Ommin - was subtly referenced in Rae Carson's adult novelization of Star Wars: The Rise of Skywalker. Asog is entirely new to Star Wars lore.
Even the references to the Jedi are interesting, suggesting the seeds of the Jedi Order were sown on numerous worlds; Ossus was the Jedi homeworld in the Expanded Universe, already re-canonized; the ancient sanctuary of Jedha appeared in Jedi: Fallen Order game.
