Solar System

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A classy map of the Sol System. Don't ask us what the hell happened to Uranus however.

A general introduction to the neglected celestial bodies of humanity's home system in 40k.

Sol/Sun

It is the sun, yellow, G Class, with 5 billion years of life left under normal circumstances. General graveyard of heretics and their possessions (no pun intended).

Mercury

Mining world. That's it. Literally. The lore is that long. However much ore is left after tens of thousands of years is a matter of debate.

Venus

An Imperial forge world. Before the Great Crusade it was ruled by the War Witches, whoever they are, but was brought under the control of the Imperium by the early Iron Warriors.

Earth/Holy Terra

The capital planet of the Imperium, the homeworld of mankind and the most important world in the whole of the Imperium. Unless you are an astronaut, you are here.

Luna/Moon

Used to be ruled by gene-cults with a lot of growth vats before the Emperor set off uniting the Solar System. Refusing to be annexed and sending the envoy back as a somehow living sack of flesh, this caused big Emps sent the XVIth Legion(and co.) upon them, with the gene-cults finally saying "OK, we surrender, call off your wolves." As such, the Luna Wolves were christened.

Mars/Sacred Mars

Home of the Adeptus Mechanicus, and the biggest forge world of all by several degrees of magnitude. Phobos is also a Mini Forge World / Defense Platform while Deimos got moved to Saturn.

Jupiter

A gas giant Forge World. The Imperial Navy's foremost shipyard and drydock. It only makes ships. It is a hotly contested Imperial political debate as to whether Jupiter is soverign to the Mechanicum or the Imperium. They went totally green though, the hippies.

It once had a Forge Moon, Ganymede, in orbit. It is now Perdita. Do NOT go near Ganymede.

Saturn

Though an inhospitable gas giant, the rings and many of the moons of Saturn were populated prior to the Great Crusade and formed a pocket empire called the Saturnyn Ordo that were occupied by some unnamed Xenos race. Given the Ordo's forces were called Void Hoplites, they were likely the Greeks to Terra's Romans.

The worlds were swiftly liberated by the fledgling Imperium and were absorbed fully shortly thereafter where they became one of the first recruiting worlds of the Solar Auxilia and formed a cornerstone of the Imperial Army.

At some point during the Horus Heresy, the Saturnyn Ordo was seemingly dismantled and the rings and moons of Saturn were designated a quarantine zone by Malcador. Access became heavily restricted as he forwarded his plans to create the Grey Knights under the veil of secrecy with standing order to destroy any unregistered ships that approach.

Later, the moons were ravaged by the Night Lords Legion during the Solar War as a prelude to the invasion of Terra. Though the depopulation of the planet probably aided in keeping the secrets of the Inquisition after the war ended, and the planet and its moons have remained an Inquisitorial stronghold ever since.

• Titan - Homeworld of the Grey Knights chapter. Is itself orbited by Deimos, once the moon of Mars that has since been relocated. It now acts as the Grey Knight's own private Forge World.
• Encaladus: Once upon a time this was the capital of the Saturnyn Ordo, where they signed the treaty with the Emperor and joined the Imperium. Is now the Palace-Fortress of the Ordo Malleus where many inquisitors have private estates.
• Iapetus: Formerly home to a hold-out of anti-Imperial rebels who fought against the Death Guard and lost. Is now home to a naval fortress, although they serve the Inquisition and Grey Knights almost exclusively.
• Mimas: Inquisitorial prison, holding the worst criminals kept in isolation and guarded by psychic wards, gun servitors and their own Stormtrooper regiment.
• Tethys: Designated a Death World due to daemons trapped on the surface that are used as a training tool for aspirant Grey Knight Paladins who need to go to the surface and make a pilgrimage without wearing their armour. Canon differs on whether Tethys is also the location of the archive of the massively fortified Librarium Daemonica or whether it is located on Titan itself.

Uranus

Uranus has no solid surface and its 27 moons were too small for permanent settlement (The largest: Titania is less than half the radius of Luna). Nevertheless, it was surrounded by a series of orbital cities populated by peaceful artisans called the Azurites.

They built a stable warp route called the Elysian Gate which was one of two in the system, allowing safe access to the Mandeville points in the Sol System.

The Azurites agreed to become absorbed into the Imperium of Man, but were assaulted by pirates who infected them with a psychic plague called the Screaming, which was contagious through sound.

The Imperial Fists purposefully deafened themselves and fought their way to the heart of the Azurite station, and self-destructed it to prevent the plague from spreading.

For their sacrifice, the Emperor ordered the Bell of Lost Souls to ring for the first time.

Despite the small size of its moons, they were heavily fortified during the Horus Heresy.

Neptune

Neptune's moons were settled during the Age of Terra some point between M15-M18, though the population devolved into hideous mutants.

The IXth Legion were given the task of bringing them to compliance, and fought a bloody war through the tunnels of its moons that cost them 12,000 men, though due to the beneficial quirks of their gene-seed they were able to replenish those numbers directly from the conquered mutant population.

The moons of Neptune were frequently infiltrated by chaos or genestealer cults at later periods.

Pluto

Rogal Dorn seems to have killed Alpharius during the Battle of Pluto in the Horus Heresy.