Colonization of the outer Solar System is subject to only 0.01 rem a day. When NASA carried out a study called "HOPE" (Revolutionary Concepts for Human Outer Planet Exploration) regarding the future exploration of the Solar System, the target chosen was Callisto. It might be possible to build a surface base that would produce fuel for further exploration of the Solar System. The Keck Observatory announced in 2006 that the binary Jupiter trojan 617 Patroclus, and possibly many other Jupiter trojans, are likely composed of water ice, with a layer of dust. This suggests that mining water and other volatiles in this region and transporting them
Solar System disc-like regions of cosmic dust. The first, the zodiacal dust cloud, lies in the inner Solar System and causes the zodiacal light. It was likely formed by collisions within the asteroid belt brought on by gravitational interactions with the planets. The second dust cloud extends from about 10 AU to about 40 AU, and was probably created by similar collisions within the Kuiper belt. The inner Solar System is the region comprising the terrestrial planets and the asteroid belt. Composed mainly of silicates and metals, the objects of the inner Solar System are relatively close to the Sun; the radius