Basis

Basis is the largest natural satellite of the gas giant Threshold in the Soell system.

Description
Basis is the largest of the twelve satellites orbiting the gas giant Threshold in the Soell system of the Milky Way galaxy. Silvery-gray in color, Basis has a diameter of 23848 km, nearly double that of Earth. Halo Installation 04 was positioned in the L1 Lagrange point between Basis and Threshold. Debris left over in the wake of Installation 04's destruction often rained down on Basis, creating small craters on the moon's surface.

Forerunner era
Sometime before 97,445 BCE, the L1 Lagrange point of Basis and its parent body, Threshold, was used by the Forerunner ecumene as the location of Installation 04, or Alpha Halo, one of the ecumene's seven ring-shaped superweapons that made up the Halo Array.

Human-Covenant War
After Installation 04's destruction, a group of Covenant defectors built a makeshift camp on Basis, amid the wreckage of the ring. During a skirmish over Threshold following the Battle of Installation 04, Cortana maneuvered John-117's GA-TL1 Longsword into the gravity well of the moon to slingshot the fighter around Basis to avoid Covenant attacks.

Post-war
After the war, Spartan-IVs were sent on reconnaissance to Basis in order to survey the debris of Alpha Halo scattered across the moon's surface. The mission marked the first use of the VECTOR-class Mjolnir armor.

Trivia

 * Originally, the level The Arbiter was supposed to take place on the moon Basis, instead of the gas mine over Threshold.
 * Basis's texture in Halo: Combat Evolved appears to be a color-graded image of Mars's surface.
 * The blue coloring of Basis when seen from space is puzzling, considering that from the surface it has a hazy orange or rust-colored atmosphere and terrain. The ruddy atmospheric coloration from the ground may result from the ash and smoke thrown up by the flaming wreckage of Installation 04.

List of appearances

 * Halo: The Fall of Reach
 * Halo: Combat Evolved
 * Halo: The Flood
 * Adjunct
 * Halo: First Strike
 * Halo 2
 * Halo: Evolutions - Essential Tales of the Halo Universe
 * The Mona Lisa
 * Halo: Combat Evolved Anniversary
 * Halo 2: Anniversary
 * Terminals
 * Halo: Escalation
 * Halo 5: Guardians