Substance

Substance is a greenish-blue gas giant in the Coelest system. It is the fourth planet in the system and is the planet which Installation 05 orbits. Though it masses more, it is similar to the planet Uranus in color and composition, being classified as an ice giant. Substance is orbited by eight satellites, only one of which, Opusculus, is a natural moon. The rest include Installation 05, and six dormant Forerunner facilities on predetermined orbital paths.

Unlike on Installation 04, where its parent planet Threshold could be seen quite clearly, especially at night, on Installation 05, Substance is very difficult to see in the sky of Installation 05. In fact, in none of the locations on this ring seen by UNSC forces (namely the Control Room, the Library, and various ruined structures) can the planet be seen. This is due to the Delta Halo's stormy weather conditions caused by a Flood outbreak that occurred some two centuries before the Battle of Installation 05.

Trivia

 * While not named during Halo 2, the file containing the planet's graphics were found to be named "Substance". Similarly, there was a file called "Threshold and Basis" in Halo: Combat Evolved. The planet was first officially identified in Halo: The Essential Visual Guide.
 * It is possible that Substance is host to a gas mining facility similar to the one found on Threshold. The two planets are very similar, and they both gravity anchors for Halos.

List of appearances

 * Halo 2
 * Halo: Ghosts of Onyx