Isolum is a planet located in the Pacificus Segmentum, in the Sabbat Worlds. The planet was part of the Imperium of Mankind and served as the headquarters to the Knights of Redemption Space Marine chapter.
Originally an Ork savage world, Isolum was the base to a smaller Ork tribe that inhabited the planet for an unknown amount of time. Due to the hostile temperature, only little of the planet was controlled by the Orks, and most were withdrawn into bases on the surface of the planet, and even then they were only in small numbers. The Orks had no way of withdrawing from the planet, for their Rok was destroyed during their landing on the planet.
Soon, the Imperium of Mankind would get report of the Ork presence on the planet, and soon the Knightsof Redemption chapter was sent to eliminate it, and shortly after the marines of the 4th company moved to pacify the planet.
Isolum was an Imperial Ice World, with many glaciers and frozen oceans present. The planet made it's self almost uninhabitable following the freezing of the oceans, and the hostile climate, while the planet did have a proper gravity level.
On the surface, Isolum showed signs of past civilization, in forms of obselete buildings that were spared after the planet had frozen, however, the current climate no longer sported colonization, and was rendered almost impossible to most species without terraforming the planet. Apart from the riches that lay burried deep into the ocean, the planet held little value at the time, most having been stripped long before even the Orks had arrived.
While unconfirmed, mainly due to the inability to detect Necron life using a scan, as well being unable to dig without freezing to death, it's speculated a Necron tombworld exists under the surface of Isolum.