The Sethis System is composed of one star, one major planet, and three moons of varying character and hostility. What follows is a brief account of each body, compiled from fragmentary geologis surveys, Mechanicus reports, and the testimonies of those few souls who have travelled between them and lived to tell the tale.
Toricum IV is an aging red dwarf, bloated and dim. Its light barely reaches Sethis Major, and what little warmth it provides is negligible compared to the geothermal heat extracted from the planet's volcanic core. The star's name comes from an obscure saint venerated in the Macharian Sector, though whether Saint Toricum would be flattered or insulted by the association with such a feeble celestial body is a matter of theological debate the Adeptus Ministorum has wisely chosen not to pursue.
Augur readings suggest Toricum IV has perhaps another two million Terran years before it collapses entirely, at which point Sethis Major will become truly uninhabitable. The Tech-Priests of Mars find this timeframe acceptably distant and have filed the star's inevitable death under "problems for future generations." The citizens of Omin, who live and die within the span of decades, care even less.
Sethis Major is a barren, frozen rock. It is only a small planet, lying so distant from Toricum IV that the planet's surface is covered in permafrost and receives no more than three hours of sunlight a day. For its citizens, this means that day-to-day life is a benighted affair, the vast majority of the planet's natural light coming from the horrific Rictus Borealis, which hangs in the sky like an open wound, casting everything in shades of crimson and shadow.
In the centuries since the planet was settled, it has only been very roughly catalogued by geologists of the Adeptus Mechanicum who sought to understand the resources that the planet had to offer. What they found was grim but serviceable: metals, minerals, and—most importantly—heat. The rest of the planet they dismissed as "uninhabitable wasteland" and moved on.
The planet's South Pole is a vast mountain range called the Ataxan Plateau. The mountain range spans many thousands of miles and its tallest peaks offer breathtaking vistas of the snow-blasted wasteland that makes up the majority of the planet's surface. No permanent settlements exist here, though occasional Mechanicus expeditions venture into the range in search of rare mineral deposits. Most do not return. Those that do speak of howling winds, temperatures that freeze promethium in its tanks, and shapes moving in the blizzards that are not entirely explicable by natural phenomena.
The Inquisition maintains a watching brief on the Ataxan Plateau but has thus far declined to commit resources to a full investigation. There are, after all, more pressing threats in the sector, and if something unnatural lurks in the frozen south, it has thus far shown no interest in leaving.
The equatorial belt is slightly more temperate than the poles—though "temperate" is a relative term on Sethis Major, meaning only that a human might survive for hours rather than minutes without thermal protection. The belt has not been deemed fit for settlement due to the thick rock crust beneath the surface, which offers stiff resistance to the mining and energy extraction projects that make up the Imperium's chief concern on Sethis Major.
A few hardy souls have attempted to establish outposts in the equatorial wastes, drawn by promises of unclaimed land and freedom from the Adeptus Mechanicus' oversight. Most of these settlements failed within a generation. A handful endure, eking out miserable existences as scavengers, smugglers, and worse. The Adeptus Arbites occasionally mounts punitive expeditions to root out particularly troublesome enclaves, but for the most part, the wastelanders are left to their own devices. They pose no threat to Omin, and the Imperium has learned that some problems are best solved by simply ignoring them until they freeze to death.