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,
One of Our Planets Is Missing One of Our Planets Is Missing "One of Our Planets Is Missing" is the third episode of the first season of the animated American science fiction television series "". It first aired in the NBC Saturday morning lineup on September 22, 1973, and was written by veteran "" director Marc Daniels. In this episode, the "Enterprise" must contend with a massive space cloud that eats planets, now targeting a Federation colony of over 82 million. On stardate 5371.3, the "Enterprise" encounters a giant cloud that consumes planets that lie in its path. They determine it is heading for Mantilles, home