In the late 40th Millennium, however, warp storms engulfed the planet, summoned by the Great Unclean One Ulkair in his battle against the Blood Ravens. Chapter Master Moriah and Azariah Kyras sealed the Greater Daemon within the heart of the planet, but the damage was done. Aurelia disappeared into the Warp, and remained there for a millenium, frozen into a perpetually-shifting Ice World devoid of all realspace-dwelling life. In late M41, Aurelia emerged back into realspace at the behest of Chaotic forces (led by Araghast and Eliphas of the Black Legion) who wished to free Ulkair and wreak havoc on the sub-sector. Through the efforts of the Blood Ravens' Third and Fifth Companies, Ulkair was banished back into his prison and the Black Legion was thwarted.
From then on, the Imperial Guard stationed a number of regiments to keep watch on the planet, at least one of which fell under the thrall of Ulkair.