Jupiter

Everyone's favourite giant gas ball.

Astrographical map of Jupiter during the Horus Heresy.

Jupiter is a gas giant and the largest planet in the Solar System, dwarfed only by Sol itself. Most people know it for the big fuckoff storm that's raging on it in the present day. Neckbeards know it as the beating heart of the Imperial Navy.

Overview

Humans have probably known of Jupiter since prehistoric times (since it being the 3rd brightest object in the night sky, behind Venus and (obviously) the Moon, means it's pretty fucking hard to miss), though obviously they wouldn't know what it was for a long time. The first records we have of it being observed in any capacity come from Babylon in around 7-8,000 BC. (So around the time the Emprah was born, if you don't know your dates.) The ancient Chinese also based a bunch of shit off their observations of Jupiter's orbit of ~12 years, such as the well-known Chinese Zodiac - though a Hellenistic Greek astronomer would later narrow that orbit down to the scientifically-accurate 11.86 years, meaning the Zodiac is by now well out-of-sync with Jupiter. It's also one of the classical planets of alchemy, representing tin and being associated with Thursday.

Come the 17th century, and good ol' Galileo invented the telescope and chose to demonstrate it by looking at Jupiter. As such, he's credited with discovering that Jupiter has moons, among other things he saw with the nifty sight-extender. Others would continue in his footsteps (as he was unfortunately imprisoned for going against Church dogma) and figure out a fuckton about the Solar System's overweight gasball. Around this time the famous Great Red Spot, a giant storm that dwarfs the Earth, started on Jupiter and has been raging ever since.

Jupiter is the fifth planet from the Sun, and also the most massive by a large margin (having two-and-a-half times the mass of all the other planets combined). It's something of a gravitational bully, as it tugs on anything that dares to get even remotely close to its orbit. It's even believed that an early Jupiter is the reason why none of the inner solar system planets are gas giants themselves - it just ate most of the mass that could make them giants in the first place.

Warhammer 40,000

Jupiter is one of the key Forge Worlds and Mining Worlds in the Sol System and, as with all forge-worlds, it is a vast manufacturing center. It is the base of the orbital Jovian shipyards.

History

During the Age of Strife, Jupiter's moons became occupied by Xenos overlords which enslaved the human inhabitants and did typical Age of Strife stuff to them. These moons were not liberated from alien control until the coming of the Emperor in the early days of the Great Crusade. The Human Jovian Void Clans were utilized by the Emperor during the Great Crusade where their shipyards gained fame for producing massive amounts of high-quality warships thanks to technology they guarded even from the Mechanicum.

During the Horus Heresy Jupiter was the center of Rogal Dorn's third defensive sphere under the command of Imperial Fists Captain Efried. In the later stages of the Solar War, the massive array of moons and orbital habitations of Jupiter were captured by Iron Warriors forces led by Perturabo. Instead of reducing every pocket of loyalist resistance or wasting his time during his drive to Terra to occupy the many habitation zones around Jupiter, Perturabo in an unorthodox and un-Perturabo move, instead unleashed fleets of Pirates, traitor Imperial Army, Night Lords, and Emperor's Children to terrorize and subdue the region. Jupiter was subsequently reclaimed by the Imperium during the Great Scouring after the traitor defeat in the Siege of Terra.

Overview

Jupiter is de facto the homeworld of the Imperial Navy. The space docks and workshops that circle Jupiter, like a ring of moons, are home to the millions of technomat and drone Servitors that work under the supervision of Artisan and Rune Priest Tech-priests to build the Imperial Navy's warships.

It is known that as far back as the Horus Heresy, Jupiter held industrial and colonial cohorts with clouds of satellites along with Trojan asteroids containing human colonies, factories along with forges. The Jovian colonies were powered by the radiation that surged from the massive planet and much of the industry fed on the mineral riches that had been yielded from centuries of exploitation, with its full potential having not been fully exhausted. Due to these factors, Jupiter served as Terra's shipyards and its skies were always filled with starships with spacedocks and fabricatories around the various moons that worked tirelessly to construct anything from single manned Raven Interceptors to gargantuan hulls of Emperor-class Battleships.

Each of the Imperium's ship designs is associated with a single shipyard: the Emperor, Tyrant and Dominator are typical of the spaceships produced at the Jovian shipyards.

Moons of Jupiter

Jupiter has a shit ton of moons, so here is a list of the most relevant ones:

• Ananke: This moon is known to have had habitats on its surface by the era of the Horus Heresy.
• Iocaste: This moon is known to have had habitats on its surface by the era of the Horus Heresy.
• Europa: Located within the Galilean range, Europa had been geo-engineered into an ocean-moon by the time of the Horus Heresy.
• Io: One of the moons in the Galilean range that had a seething orange mass by the Horus Heresy.
• Ganymede: The largest moon of Jupiter with the shipyards centering around it as well as the dozen other smaller moons. It has since been transformed into a Hub-Fortress for the Indomitus Crusade.
• Thule: An asteroid moon that served as the clandestine shipyard for the Furious Abyss and was destroyed by renegade members of the Adeptus Mechanicus during the Horus Heresy.
• Callisto: A moon of Jupiter known to hold residential orbitals above its surface by the Horus Heresy.
• Lysithea: Moon of Jupiter that during the Age of Strife was occupied by Xenos. The moon was liberated by forces of the early XIXth Legion during the Great Crusade.

Orbital Plates

• Polar Shoal City-Stations: Vast space colony conglomerations that spread across Jupiter's northern pole. Home to the ruling class of Jupiter.
• Saros Station: This space station in orbit around Jupiter resembled a vast spindle bathing in crimson glow which made it appear as if it were crystal chandelier that had been severed from its mounting and thus cast free into the void. Unlike the majority of the gas giant's industrial and colonial cohorts, the station had been a resort platform before the Horus Heresy, where the Jovian elite found respite as well as diversion from the works of the shipyards and manufactories. It was said that only the Venus orbitals could surpass Saros Station in luxury with its avenues of gold and silver, null-gardens, auditoriums along with the finest opera houses outside the Imperial Palace.
• Kadal: Satellite munitions fortress. It was the site of an Alpha Legion-instigated anti-Imperial revolt during the Horus Heresy. Subsequently destroyed during the Solar War.

Other Place of Interests

• The Caul: Sphere of debris that surrounds Jupiters shipyards which extends deep into space in every direction. This debris field is home to mazes of equatorial breaker yards that gather scrap and dissemble or retrofit vessels.