Terrestrial planet Terrestrial planet A terrestrial planet, telluric planet, or rocky planet is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun, i.e. Mercury, Venus, Earth, and Mars. The terms "terrestrial planet" and "telluric planet" are derived from Latin words for Earth ("Terra" and "Tellus"), as these planets are, in terms of structure, "Earth-like". Terrestrial planets have a solid planetary surface, making them substantially different from the larger giant planets, which are composed mostly of some combination of hydrogen, helium, and water existing in various
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.