The Velixum system is a solar system located in the Segmentum Obscurus (Scarus Sector, Antimar Subsector), comprising eight worlds in orbit around a red supergiant star. The worlds are of varying size and consistently have traits of desert worlds, with very little natural water. Many of the worlds were, accordingly, depending on Velixum VIII for water, which is, conveniently, an Ice world.
The system was discovered in early M36 through usage of a Mechanicus "warp-probe" - essentially an unmanned craft with poor, expendable cartographical and tracking equipment that is launched through the Astromonicon in the hopes that it will start sending back information of an undiscovered location, heralding the arrival of a colonisation fleet. After a debate between the Mechanicus and the Imperium, a heated albeit verbal conflict that exemplified the independence from the Imperium the Mechanicum effectively held, the Triad Velixumis was formed not only as a treaty of terms as to who would have rights to the three main worlds in the system, but that they would be uniquely set up to dependently co-operate with each other rather than becoming self-sufficient in their own right - a successful social experiment if there ever was one.
In 893 M41, the system fell victim to a massive invasion by the Necrons, who advanced through the planets starting from the outermost, effortlessly destroying all resistance until the Battle of Velixum III.
The closest planet to the sun, that has thus far went untouched, declared a Dead World due to its lack of breathable atmosphere and dangerous proximity to the system's sun. Adeptus Mechanicus scouts sent to the world burnt to death, or, in the case of those who were able to avoid the unforgiving heat of the sun, apparently went out of contact. Com-links descended into eerie static as these scouts landed, and anything trackable from orbit either failed or somehow became untrackable. During the Necron invasion of Velixum, it escaped attack.
The next in line from Velixum I (but still a considerably great deal away), Velixum II was originally a Desert World until it was industrialised, and later became a Hive World with vast cities. It is famous for its industrial output of infantry-level armour and ballistic weaponry, supplied by raw materials brought from Velixum IV, which is of noteworthy quality in comparison to similar output from other Hive Worlds. It was the place were the devasted Imperial forces in the Velixum system regrouped in the wake of the Necron invasion, and where the Velixumite 5th Rifles were formed. It was the last to be invaded during the Necron invasion of Velixum.
The third planet from the sun and yet still very far away from Velixum II, Velixum III was a Civilised World with a high quality of life as far as such worlds went, especially so considering that it was technically a Desert World still. Disparangingly refered to as an "advert planet" due to its role as the tertiary centre of the Triad Velixumis, Velixum III barely escaped classification as a Paradise World in M38 after the world was fully developed, and yet it still remains a popular stop-off point for offworld traders on account of the "attractions" the planet has. It consisted of two continents with a single ocean between them, with a small web of lakes and rivers spanning through each continent. These are inhabited by native aquatic life, and at their banks, small amounts of flora grow. Notable landmarks were Neomars Valley, which contained the deepest point on the planet's surface, the Thanas Mountains and the Zaora Desert. Its capital city was Athenor Prime. It had four moons, most of which were used as Mechanicum research bases, apart from Argonis, which served as a small Penal World. It was the second last to be invaded during the Necron invasion of Velixum.
The fourth from the sun and the home of the Velixumite 4th Rifles. It was a Desert World that was colonised and later used as a Mining World, forming the primary backbone of the Triad Velixumis. It had virtually no natural water apart from in the atmosphere and deep underground and few native lifeforms, apart from the hardy "Dunedogs", powerful canine-like animals, and a couple of smaller species. Even after it was developed and infrastructure was established, the harsh weather conditions ensured that a strong frontier spirit remained in the labouring populace. The battle in which it fell during the Necron Invasion was extremely bloody and involved virtually every Imperial Guard force in the system, and culminated in being destroyed by Cyclonic Torpedoes by the Vigilant Blades Space Marines chapter.
A Desert World with ever-so-slightly more water than Velixum IV. It was a large, high-G planet that fell under Feudal World classification with a high population of an Ogryn subspecies which adapted to the harsh desert environment, making them even hardier. This world was a primary source of Ogryn troops for Imperial Guard regiments throughout the Segmentum Obscurus. It was the fourth planet to fall to Necron invasion in the system, and there were no actual survivors apart from the Ogryn who were part of Imperial Guard regiments.
A helium-rich gas giant that served no real purpose in the system. However, several battles during the Necron invasion of the system took place on its three mineral-rich moons, on which small mining outposts and research stations had been established.
A Civilised World that, while primarily covered in desert, actually escaped such a classification due to the prominence of woodland, swamps and oceans in the southern regions of the planet. It became the secondary supplier of water for the system after Velixum VIII fell, but the rest of the system found itself in a considerably sticky situation after it fell a few years later.
The furthest planet from the sun which led to the freezing of much of the atmosphere's water due to the subzero temperatures. It was a small planetoid, technically a Mining World, primarily inhabited by humans living in specialised, insulated compound-domes, alongside Ratlings. Routinely, ice would be gathered, melted, purified and shipped off to the other worlds in the system which had considerably less water, which was a primary source of income. It was the first to fall during the invasion.