Jupiter and liquid matter. It is the largest of the four giant planets in the Solar System and hence its largest planet. It has a diameter of at its equator. The average density of Jupiter, 1.326 g/cm, is the second highest of the giant planets, but lower than those of the four terrestrial planets. Jupiter's upper atmosphere is about 88–92% hydrogen and 8–12% helium by percent volume of gas molecules. A helium atom has about four times as much mass as a hydrogen atom, so the composition changes when described as the proportion of mass contributed by different atoms. Thus, Jupiter's
Colonization of the outer Solar System one of Neptune's satellites could be used for colonization. Triton's surface shows signs of extensive geological activity that implies a subsurface ocean, perhaps composed of ammonia/water. If technology advanced to the point that tapping such geothermal energy was possible, it could make colonizing a cryogenic world like Triton feasible, supplemented by nuclear fusion power. The noted physicist Freeman Dyson identified comets, rather than planets, as the major potential "habitat" of life in space. There would be many problems in colonizing the outer Solar System. These include: Colonization of the outer Solar System Many parts of the outer Solar System have