Substance
From Halopedia, the Halo wiki
Substance is the name of the blue gas giant around which Installation 05 orbits. While not named during the game, the file containing the planet's graphics was found to be named "Substance." Similarly, there was a file called "Threshold and Basis" in Halo: Combat Evolved. It is unknown if there is a gas mine on Substance like Threshold.[1]
