Solar Terrestrial Planets
Earth's 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 they have all merged with, or been ejected by, the four remaining worlds in the solar nebula.
Dwarf planets, like Ceres and Pluto, and other large asteroids 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 and Pluto have a density of 2.1 g cm−3, and Haumea's density is similar to Pallas's 2.8 g cm−3).
Read more about this topic: Terrestrial Planet
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