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 vapour and could be indicators of liquid water deeper down. It could also be just ice. In June 2009, evidence was put forward for salty subterranean oceans on Enceladus. On April 3, 2014, NASA reported that evidence for a large underground ocean of liquid water on Enceladus, moon of planet Saturn, had been found by the Cassini spacecraft. According to the scientists, evidence of an underground ocean suggests that Enceladus is one of the most likely places in the solar system to "host microbial life". Emissions of water vapor have been detected from several regions of the dwarf planet Ceres.