Threshold
From Halopedia, the Halo wiki
Summary
File:Gas Mine.jpg
A Phantom approaches the gas mine in Threshold's atmosphere.
Threshold is a large gas planet. Before its destruction, Installation 04 orbited between it and its moon Basis. In Halo 2, the Heretics took refuge on a Forerunner Gas Mine in its atmosphere before the Arbiter and his Special Ops troops dropped it into Threshold's depths. Threshold is a Neutral planet.
Trivia
In Halo 1, the Assault Rifle has a small digital display that shows how much ammo you have left in your clip as well as a indicator that points to Threshold, acting like an off-world compass.
