From Halopedia, the Halo wiki
An oddity among Sol's gas giants, Uranus is mostly unexplored and uninhabited by humanity, as its distance from Sol makes traveling there costly. Its moons are poorly-understood when compared to those of Jupiter. Despite this, Uranus has a number of distinctive features that separate it from its neighbors. Firstly, its axial tilt has turned its poles past a 90o angle to the orbital plane. Secondly, Uranus has a number of anomalous radiation spikes that have not been addressed or explained.