Grunt Homeworld

The colloquially-named Grunt Homeworld is the planet from which all of the Covenant Unggoy (Grunt) race originally migrated from.

"Ancient stepping-stones" of Forerunner creation can be found on this planet. There intended purpose is unclear. According to a comment here, the stones are also mentioned in one of the novels.

Topology and Climatology
The Grunt Homeworld is believed to mirror the Human homeworld Earth in that it appears it has two or more climatic zones - swampy and hyperborean. It is noted to have swamps interlaced with "naturally occurring pillars of fire", marshes, and ponds. This might occur at the equatorial regions. However, it is also noticed to be of extreme low temperatures in other locations, probably like the poles.

It should be noted that the Grunt Homeworld may not necessarily be one uniform biome or temperature like stereotypically conceived in science fiction. Most known worlds are different biomes existing adjacently with respect to each other.

Atmosphere
The atmosphere is mainly of methane (CH4), which has been noted to be necessary for Grunt life, possibly even cellular respiration.