Basis

Basis is the largest natural satellite orbiting the gas giant Threshold in the Soell system.^[1] Silvery-gray in color, the moon is 23,848 kilometres (14,818 mi) in diameter,^[2] nearly double the size of Earth. Halo Installation 04 was positioned in the Lagrange point between Basis and Threshold.^[1] After Installation 04's destruction, a group of Covenant defectors built a makeshift camp on Basis, amid the wreckage from Alpha Halo.^[3] Debris from Installation 04 often rained down on Basis, creating small craters on the moon's surface.^[4] 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.^[5]

Trivia

The surface of Basis

Originally, the level The Arbiter was supposed to take place on the moon Basis, instead of the gas mine over Threshold.^{[citation needed]}
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.