Terrestrial planet from the original solar nebula. The Solar System has four terrestrial planets: Mercury, Venus, Earth, and Mars. Only one terrestrial planet, Earth, is known to have an active hydrosphere. During the formation of the Solar System, there were probably many more terrestrial planetesimals, but most merged with or were ejected by the four terrestrial planets. Dwarf planets, such as Ceres, Pluto and Eris, and small Solar System bodies are similar to terrestrial planets in the fact that they do have a solid surface, but are, on average, composed of more icy materials (Ceres, Pluto and Eris have densities of 2.17,
Extraterrestrial liquid water the existence of a sub-ice ocean is inferred from the measurements of the magnetic field of Jupiter. Since conductors moving through a magnetic field produce a counter-electromotive field, the presence of the water below the surface was deduced from the change in magnetic field as the moon passed from the northern to southern magnetic hemisphere of Jupiter. Thomas Gold has posited that many Solar System bodies could potentially hold groundwater below the surface. It is thought that liquid water may exist in the Martian subsurface. Research suggests that in the past there was liquid water flowing on the surface, creating