The Oort cloud (/ˈɔrt/ or /ˈʊərt/1) or Öpik–Oort cloud, named after Dutch astronomer Jan Oort and Estonian astronomer Ernst Öpik, is a spherical cloud of predominantly icy planetesimals believed to surround the Sun at a distance of up to 50,000 AU (0.8 ly). This places the cloud a quarter of the distance to Proxima Centauri, the nearest star to the Sun. The Kuiper belt and the scattered disc, the other two reservoirs of trans-Neptunian objects, are less than one thousandth as far from the Sun as the Oort cloud. The outer limit of the Oort cloud defines the cosmographical boundary of the Solar System and the region of the Sun’s gravitational dominance.
The Oort cloud is thought to comprise two regions: a spherical outer Oort cloud and a disc-shaped inner Oort cloud, or Hills cloud. Objects in the Oort cloud are largely composed of ices, such as water, ammonia, and methane.
Astronomers conjecture that the matter composing the Oort cloud formed closer to the Sun and was scattered far into space by the gravitational effects of the giant planets early in the Solar System’s evolution. Although no confirmed direct observations of the Oort cloud have been made, it may be the source of all long-period and Halley-type comets entering the inner Solar System, and many of the centaurs and Jupiter-family comets as well. The outer Oort cloud is only loosely bound to the Solar System, and thus is easily affected by the gravitational pull both of passing stars and of the Milky Way itself. These forces occasionally dislodge comets from their orbits within the cloud and send them towards the inner Solar System. Based on their orbits, most of the short-period comets may come from the scattered disc, but some may still have originated from the Oort cloud.
The Oort Cloud is the only human settlements not controlled by the USH. After the Triton Conflict, many dissidents from Triton and other supporters moved to the cloud. They set up a variety of miniature colonies throughout a tiny portion of the cloud, living off the materials they find. Many pirates, deserters, and visionaries live within the cloud. The USH will not spare the resources to make a Darkgate out in the cloud so for the time being the area is safe.