Illum is a warm ocean planet rich in oxygen giving it its distinctive blue color and making it naturally habitable to humans, and due to its distance from its parent star, the waters are very temperate and hospitable, making the human populace on the planet have no need to wear protective suits or retreat within pressurized structures. This water remains the same temperature across the entire planet, even towards the core.
Like all ocean planets, Illum's surface is completely covered in water. However its ocean is completely comprised of fresh water, drinkable to humans. This has lead to the planet to be come an important water resource for nearby star systems that lack bodies that contain it.
The planet exists in a duel-planet system with its sister-world Autum, meaning the two celestial bodies orbit each other rather than one orbiting the other. Though due to it being larger, Illum is the planet in the system while Autum remains the moon.
Its years are extremely long, lasting around two thousand nine hundred and twenty four standard years. This is because when its moon Autum became gravitationaly bound to Illum its orbit around its parent star, Indicum, was slowed to a crawl. Leaving the planet with its piratically three millennia years we see today.
It holds one major colony, Aqua-Illinium. Here, the populace of Illum gathers fresh drinkable water and sends it to nearby star systems who lack the ability to gather fresh-water themselves, this causes the planet to be quite economically prosperous.
It, and its moon Autum, served as the second battlefield of the First Alliance War. This battle, known as the Battle of Illum and Autum was caused because to the Indicum System and its respective worlds defecting to the newly formed True Alliance of Man. And due to Illum being a very important resource to nearby star systems, an invasion of the planet and its moon was launched. However, because the Human Alliance of Ambrosia was unaware of how powerful the True Alliance's military was, they were quickly overwhelmed and control of the planet remained under the True Alliance.
Illum formed alongside the formation of its parent star Indicum around 1,178,000,000 BCE. When the planet first formed, it was a cold ice-world with an average year length of three hundred and sixty five standard days. This icy surface was originally comprised of almost entirely half frozen oxygen, and half frozen water.
The planet would remain this way for millions of years until' the once temperate terra planet Autum would be captured by the planet's gravity, slowly traveling within its orbit. Ultimately culminating when the former planet would be permanently captured by Illum's gravity in 546,000,000 BCE. forming a duel-planet system.
With the introduction of Autum in Illum's orbit, the planet's icy surface would heat up significantly, melting it very quickly and forming an oxygen rich atmosphere as well as a large fresh water ocean covering the entire planet. This event also caused the destruction of all water and life on the surface of the now moon Autum, leaving it a lifeless desert world.
Illum would remain untouched by any Ambrosia Civilization until' it, and the rest of the Indicum System would be discovered by the Human Alliance of Ambrosia in 10307 CE. While the majority of worlds in the Indicum System were deemed to be too hot and not worth the expense for colonization, it was discovered that Illum could support human habitability naturally. With this a fairly large colony would be established on the planet in 10333 CE. On this colony, water is gathered from Illum's surface and is sent to nearby star systems that lack celestial bodies that contain fresh drinking water.
During the early months of the First Alliance War the Indicum System would join the True Alliance of Man as they seemed to be the better option for the star system's interests. This presented a problem to the Human Alliance of Ambrosia as Illum serves as an important resource to several star systems near Indicum, As such, the Human Alliance opted to launch a two-pronged invasion of the planet and its moon in the hopes that it would deter it, and other star systems from joining this new rebel government in 10388 CE. This attempt failed as the True Alliance military quickly overwhelmed the Human Alliance's poultry force as they were unprepared on how powerful the True Alliance's military actually was.
After their defeat, control of the planet would remain under the True Alliance of Man. And with it being a very important resource for the aforementioned nearby star systems, those worlds that rely on Illum followed suit and defected to the new rebel government as well. And after the True Alliance's dismantling it would fall under the Ambrosia Alliance of United Systems like all True Alliance colonies.