Urs

The Urs system, formally known as the Urs-Fied-Joori system, is a triple star system most notable as the home system of the Sangheili species. The system consists of the F-type dwarf star Urs (Urs A), its smaller K-type companion Fied (Urs B), and the red dwarf Joori (Urs C). Both Fied and Joori orbit Urs at a distance of several dozen AUs. Most of the major planets in the system, including the fourth, Sanghelios, orbit Urs, though both Fied and Joori host small planetary systems.

Located in the Orion Arm in the constellation Lepus approximately 3,500 light-years trailing from Sol, Urs is considered by many to be one of the closest things the Holy Ecumene has to a fixed physical core. As the hub and epicenter of the Sunlit Worlds, Urs is one of the most populated and trafficked systems in the Covenant, with several colonized planets and moons along with numerous space habitats and stations. Aside from Sanghelios, a number of other bodies in the system are fully or nearly habitable by the Sangheili (one of them, Unsfaral, orbiting Joori), which has led to some speculation at possible Forerunner ecoforming or an intervention by an even earlier civilization.

The interstellar medium within several dozen light-years around the Urs system, known as the Wreath of Urs, is relatively dense. While not a full-fledged nebula, this made early slipspace navigation relatively easy for the Sangheili, as the interstellar medium provided clear navigation routes and ample traction for the early blinker drives to drag ships along.

History
The system's trinary makeup had a notable effect on the culture and mythology of the Sangheili. Its three stars and many planets would often be cast as religious and mythological figures, with Urs frequently being a primary sun deity, Fied his consort, and Joori a wayward or banished relative, often a form of trickster god. By the time Forerunner worship became the mainstream religion on Sanghelios, the old sun-faiths were already waning or all but dead, but their legacy lived on in Sangheili culture and language. For example, the sun-deities and mythic figures named after the three stars and the planets orbiting them remained as the subject of many proverbs and greetings.

Various bodies in the system, including some of the worlds around Fied and Joori, served as a target for early Sangheili colonization efforts. After contact with the system at large was lost in the Skyfall, the space colonies developed a distinct cultural character from that of Sanghelios and would only be re-contacted centuries later.

The Urs-Fied-Joori system has no major asteroid belts, though a number of asteroids are clustered in major Lagrange points. The asteroids are unusually metal-poor and are suspected to have been depleted by extensive mining in ancient times.

Saiben
A metal-rich rocky world, Saiben is intensely volcanic due to the immense tidal forces from the Urs-Fied pair. One side of the planet is constantly in a near-molten state due to the heat. For a planet orbiting so close to a binary, its orbit is unusually stable. The planet was once revered as a servant-deity of Urs and Fied in one of the Sangheili's ancient pantheons.

Hudowan
Hudowan is a large, high-gravity superterrestrial covered in a single deep ocean that covers the entire planet. Hudowan's atmosphere is dense but not breathable, being largely composed of nitrogen, ammonia, helium as well as large amounts of water vapor. The planet has a primitive ecosystem, though several signs point to its native life having been more complex in the ancient past. Various Forerunner relics are known to be located in its depths, though only some of these have been studied.

Sanghelios
The Sangheili homeworld.

The larger of Sanghelios' moons, Suban is most notably home to the origin point of Subanese crystals.
 * Suban

A moon largely covered in oceans, Qikost is a notable aquacultural site for the Sangheili and home to various population centers. Its oceans have served as a major source of deuterium for fusion purposes since the Sangheili's early spacefaring days.
 * Qikost

Etashondo
Etashondo is a large gas giant with an intense radiation belt. This severely hampered the Sangheili's early efforts to extract helium-3. Etashondo has an expansive system of moons, though the planet's radiation belt dampened large-scale colonization.

Otazhaan
Otazhaan is a cold terrestrial world largely composed of rock and ice and a trace atmosphere of xenon and nitrogen. Its surface gets periodically warmed as it aligns with Fied on its orbital path, though these warm seasons are fleeting.

Kotaaro
A very dense superterrestrial world, Kotaaro is suspected to be a "fossil core" of a drained gas giant.

Joori planetary system
A red dwarf, Joori is orbited by six rocky or icy worlds. A number of asteroids are clustered in Joori's trojan points.

Unsobara
Joori's largest planet and the primary Sangheili colony around Joori, Unsobara is a close-orbiting terrestrial world tidally locked to Joori but has a terminator line habitable to the Sangheili. Its partially hospitable environment attracted Sangheili settlers early on, and it remains Joori's largest population center, with most of the habitable band utilized by its settlers one way or the other. Though the days of the Nirphal Resurgence are long past, and Unsobara has long stood as a relatively prosperous world of its own, the locals retain some of their unique cultural traits of old that distinguish them from those on Sanghelios or the inner Urs system.

Kaloruun
A small, barren world, Kaloruun has housed minor arcology-colonies since the early days of Joori's colonization.