Ilum

"There is no place more sacred to the Jedi."

- Jedi Padawan Ahsoka Tano, regarding Ilum's Crystal Caves

Ilum was a snow-covered planet located in the 7G sector of the Unknown Regions, within the Ilum system. In the system, Ilum was fifth from its parent star Asar, a blue dwarf, located roughly equidistant from Asar and the system's cometary cloud. Ilum had been utilized by the Jedi Order for the Gathering, a rite of passage in which Jedi younglings must find and harvest kyber crystals for their lightsabers, for thousands of standard years.

When the Jedi Order was exterminated by order of Darth Sidious, the new Galactic Empire occupied Ilum and began excavating it for its vast supply of kyber crystals, which were to be used in the construction of the first and second Death Stars. The over-mining of the planet caused a massive trench to open up along Ilum's equator.

After the fall of the Empire, its successor state, the First Order, converted the massive trench into Starkiller Base: a planet-destroying superweapon that was the culmination of the Empire's research into dark energy translations and hyperspace tunneling. The First Order's modifications allowed Ilum to act as a mobile base until it was destroyed by the Resistance in retaliation for the destruction of the Hosnian system. Following the attack, led by Poe Dameron, the planet collapsed into a star that would later be named Solo after the legendary smuggler Han Solo who died on its surface.

Description
The planet Ilum was situated in the Ilum system, a star system located in a part of the Unknown Regions known as the 7G sector. Ilum was an arctic world; that is, the entire planet was covered in ice and snow, and was therefore inhospitable to most species. Hidden beneath Ilum's frigid surface was what came to be known as the Crystal Cave. Within the maze-like crystal caves grew kyber crystals, which brought the Jedi Order to Ilum so they could harvest the crystals in a rite of passage known as the Gathering, in which Jedi initiates harvested their crystals by attuning themselves to the Force. As such, Ilum was a holy site for the Jedi Order for centuries.

Also located beneath the surface of Ilum were geysers, formed by volcanic activity on the planet. These geysers warmed some underwater bodies of water and their size or duration could change due to volcanic episodes or mineral deposition. Geological formations were also present in the caves of the planet, formed over billions of years by accumulated mineral matter, deposited from hydrothermal fluids. The planet had a kyber crystalline core.

By 18 BBY, the Empire had already corrupted Ilum, draining its resources dry as well as having destroyed entire parts of the planet's surface, as they were harvesting kyber crystals for the Death Star; the destruction was visible even from space. When Jedi Purge survivor Ahsoka Tano returned to the planet, she noted that there were at least two Star Destroyers and a mining ship in orbit around the planet. Chunks of the planet had been carved away, exposing the rock and lava that boiled up from the planet's core.

Discovery
Ilum's recorded history began tens of thousands of years before the Galactic Empire's creation. A Jedi scout performed Force-assisted hyperspace navigation through hyperspace routes, taking her to the Unknown Regions. She was drawn to a powerful resonance in the Force, which brought her to Ilum. The scout reported that Ilum was devoid of any sentient life, but was rich with non-sentient animals.

Jedi uses
Survey teams were sent out later, and ultimately discovered the vast quantity of naturally-forming kyber crystals such as pontite and mephite. The Jedi Order's High Council dispatched scholars, artisans and warriors to secure the planet. The Council decided that the planet should be kept secret to the galaxy at large. Hyperspace surveyors mapped out an uninterrupted hyperspace route from the Core World of Metellos directly to Ilum, and was incredibly complex. Eventually, all mentions of Ilum were deleted and it was kept from local, sector-wide and galactic star maps.

The Jedi Temple on Ilum remained the last sign of intelligent life on Ilum, but was almost entirely covered by ice. All other bases on Ilum were removed by the Jedi. Ilum became a bigger supplier of kyber crystals when other planets exhausted their supplies.

Clone Wars
As was tradition, a group of Jedi younglings would travel to Ilum to build their first lightsabers, aboard the Crucible and escorted by a higher-ranked Jedi. In 20 BBY, one such Gathering took place in the midst of the Clone Wars. Padawan Ahsoka Tano escorted the younglings Byph, Ganodi, Gungi, Katooni, Petro, and Zatt to the Crystal Cave, where Grand Master Yoda awaited their arrival. Each youngling endured different trials to retrieve their crystals.

All of the younglings left Ilum aboard the Crucible, where they would be instructed by the architect droid Huyang on the construction of their lightsabers.

Under the Empire
A year after the Gathering took place, the Galactic Empire was proclaimed. The Empire quickly occupied and began strip-mining Ilum, revealing magma bubbling from Ilum's core. The entrance to the Jedi Temple was destroyed to allow access to the crystal caves. A massive mining ship, as well as two Imperial Star Destroyers, stood watch over the planet to gain its riches. The Empire used geothermal energy from the planet's core to power their machinery and control the internal temperature of their industrial operations. Harmful byproducts were created as a result, causing destruction to Ilum's pristine ecosystem.

After his Master's lightsaber was severely damaged, Padawan Cal Kestis visited Ilum crystal caves to find a kyber crystal and built a new lightsaber. Although he had problems with the Imperial garrison on the planet, he was successful in his mission.

First Order occupation and conversion into a superweapon
After the Battle of Jakku, the Empire's remnants disappeared into the Unknown Regions and reorganized into the First Order. Ilum was chosen to begin development of the Starkiller project by the First Order, and over the 30 year period they continued the excavations started by the Empire, transforming the equatorial trench into Starkiller Base, with the planet's kyber crystalline core serving as the containment field for the Base's superweapon.

Thirty years after the Battle of Endor, the First Order would use the Starkiller superweapon to destroy the Hosnian system. The Hosnian Cataclysm destroyed the New Republic, and the Resistance, acting on intelligence obtained from Finn, a defected First Order stormtrooper, launched an attack on Starkiller Base in an attempt to destroy the superweapon before it could fire on their base at D'Qar.

With help from Han Solo, Chewbacca and Finn, who arrived on Ilum to disable the shield protecting the planet, the Resistance was able to destroy the thermal oscillator that prevented the Starkiller superweapon from destabilizing. The destruction of the thermal oscillator caused a chain reaction of explosions across Ilum's surface, and Ilum imploded and exploded, becoming a miniature star which became known as "Solo".

Inhabitants
Ilum was not home to a large amount of people, with just 5,200 sentient inhabitants. Of those 5,200, 45% were support crew, 30% were temporary researchers, 20% were military, and the remaining 5% were other individuals living on-world.

Locations
Ilum's main attraction was its Jedi temple, hidden beneath a large cliff of ice. Beneath that temple was the planet's massive complex of crystal caves where a vast quantity of kyber crystals could be found, and the site of the Gathering. The remainder of Ilum's surface was barren, save for canyons and mountains, though there were also forests on Ilum's surface.

During the Cold war between the New Republic and the First Order, Starkiller Base was built into its equatorial trench.

Behind the scenes
Ilum first appeared in Star Wars canon in the sixth episode of the fifth season of the animated television show Star Wars: The Clone Wars, which was titled "The Gathering" and aired on November 12, 2012. The planet originated in Star Wars Legends, where it first appeared in the junior novel Jedi Quest: Path to Truth, which was released on September 1, 2001.

In the 2019 video game Star Wars Jedi: Fallen Order, Ilum is depicted similarly to Starkiller Base. This depiction also appears in the 2017 reference book Star Wars Super Graphic: A Visual Guide to a Galaxy Far, Far Away. Additionally, the book specifies Ilum's diameter to be 660 kilometers, which is the same diameter as Starkiller Base. The connection between Ilum and Starkiller Base was officially confirmed in Star Wars: The Rise of Skywalker: The Visual Dictionary.

Non-canon appearances

 * Disney Infinity 3.0
 * LEGO Star Wars: The Force Awakens
 * LEGO Star Wars: The Skywalker Saga
 * Star Wars: Galaxy of Heroes
 * Star Wars: Galaxy of Heroes