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,
Wonders of the Solar System greenhouse planet Venus, a planet often referred to as "Earth's twin", and compares it to the vulcan geology of the Deccan Plateau. An example of Earth's interconnectivity with the solar system reveals that Jupiter's gravitational effect could potentially send an asteroid through the Asteroid Belt on a collision course with Earth, as evidenced by Meteor Crater. The same gravitational force is also shown to give the Jovian moon Io geological life (given the absence of meteor impact evidence there) as paralleled by the volcanism of Erta Ale in Ethiopia. All in all, with the universal laws of physics at play