(Oth Sonin IV)
Universe Halo Universe
System Oth Sonin System
Class Terrestrial
Atmosphere Breathable (N2, O2, Ar)
Primary Terrain Tropical Rain Forest, Magma Fields
Notable Species Jiralhanae
Technology Tier Native Tier 4 (Space Age)
Adopted Tier 2 (Interstellar)

Doisac, scientifically known as Oth Sonin IV, is the homeworld to the Jiralhanae, and is the fourth planet in the Oth Sonin planetary system. It has three natural satellites: Warial, Solrapt, and Teash, and is itself dominated by tropical rain forests, magma, and magnetism, although other than that has an environment similar to Earth's. Much of its western hemisphere appears "covered in red", which likely indicates a massive amount of lava and magma fields. Judging by its tropical climates, it is likely less than 1 AU away from Oth Sonin, as its temperatures range from -15 to 52 ℃ (5 - 125.6 ℉), making it in effect closer to its sun than Earth is to Sol. It has an atmospheric pressure of 1.3 Earth Atmospheres, and is composed mainly of Nitrogen, Oxygen, and Argon. It also has over double the gravity well of Earth, giving it approximately 2.1G. The native Jiralhanae live in warlike, alpha-oriented, patriarchal packs with an estimated population of 12.5 billion individuals. Because the Jiralhanae are a violent species and are allied with the Covenant, this planet is considered a significant to serious threat.

Doisac's orbital shape and coloring is similar to both Earth and Eayn.