Doisac

Doisac is the name of the Jiralhanae homeworld. It possesses three satellites (moons), named Warial, Solrapt, and Teash, and is the third planet of the Oth Sonin system. It can be estimated that Doisac is closer to Oth Sonin than Earth is to Sol because its surface temperature/climate is slightly more tropical, ranging from -15 °C to 52 °C (5°F to 125.6°F). Alternatively, its atmosphere may cause a natural greenhouse effect, trapping heat and warming up the planet (in a similar fashion to Venus).

From limited details available about Doisac, it can be estimated that it's environment is very Earth-like, with forests and oceans. It has been noted, however, that its terrain is dominated by magma and magnetism, hinting at high tectonic activity and rich magnetized iron deposits likely caused by the lunar tidal effects projected by its three moons. Doisac is a very war-torn land due to constant Jiralhanae civil warfare, typically between clans. This only occurred before they joined the Covenant.

Doisac's surface inhabitated by Brutes.

The statement that Doisac is a "Native Tier 4" refers to the "tiers of technological achievement" noted in the same Bestiarum, the Jiralhanae had worked their way up to this level before a devastating civil war brought the Tier level down. Until they were integrated into the Covenant's Tier 2 (Interstellar) technological systems.

Dosiac also seems to be war-torn, before the Brutes were part of the Covenant. As stated above, they had a series of wars amongst clans. When discovered, the Brutes were starting to re-discover radio and flight, and during the final months of the Human-Covenant War, it's more than likely it was a spot for battles between the Loyalists and Separatists.