|This page contains spoilers for:
|Runes (Short Story)
|Iopheas Secundus System
A rocky planet, Gath Rimmon is nearly covered by impenetrable acid oceans that are driven by constant storms. The planetoid seems to be semi-aware and is able to create creatures from its rocky surface to kill anyone who lands on the planet. All of this means that no permanent human settlements have ever been established on Gath Rimmon; in fact, merely surveying the planetoid is almost impossible.
Gath Rimmon possesses one natural satellite, called Riapax. The moon's orbit is highly irregular, with a period of 5467 years. Once every orbital period, the gravitational influence of Riapax results in the acid oceans on Gath Rimmon receding enough to allow exploration for three days.
At one point, Logis Alsmo Charis of the Adeptus Mechanicus hid a Dark Eldar artefact that he recovered, known as the Ayex Commorragh, in a vault beneath the surface of Gath Rimmon, hoping to come back to study it later.
Five millennia later, Charis returned to Gath Rimmon to retrieve the Ayex, but was almost killed by the native lifeforms. He was saved by a group of Space Wolves, who had come to the planet following a vision from the Rune Priest Kolja Ravenblade. Charis convinced the Space Marines that he was seeking a cache of archeotech, and they escorted Charis to the hidden vault. Once there, Charis turned the weapon against the Wolves, hoping to eliminate any witnesses to his study of the xenos device. He killed the Grey Hunters Lokjr and Varek, but Ravenblade was able to use his psyker abilities to call forth Gath Rimmon's acid storms, flooding the vault and destroying the Ayex. Charis was then killed by Baldr Svelok - the only one to make it off Gath Rimmon alive following the incident, as Ravenblade was mortally wounded by the acid.