Grunt Homeworld

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

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 is not one uniform biome or temperature like stereotypically conceived in science fiction. Most known habitable 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.

Speculation
The mainly methane composition of the atmosphere and swampiness (and therefore, hotness of the homeworld) has led to speculation that the Grunt Homeworld was like Earth 4.4 billion years ago - very hot, saturated with volcanoes, and with an atmosphere of mainly steam, carbon dioxide, methane, and ammonia. These atmospheric gases would be conducive to the Greenhouse Effect, increasing the temperature, and therefore, increase eutrophication and the creation of swamps.