Atlas
From Halopedia, the Halo wiki
Atlas is a UNSC colony with multiple moons. The prolonged Siege of the Atlas Moons was fought on the planet's moons by Vice Admiral Danforth Whitcomb, ending in a rare UNSC victory[1].
The planet (like the UNSC Atlas) is named after Atlas, the Greek titan who bore the world on his back.
Halo 3: ODST was codenamed Atlas by Bungie at one point in development.
