Geology of solar terrestrial planets Their size, radius, and density are all similar. Terrestrial planets have numerous similarities to plutoids (objects like Pluto), which also have a solid surface, but are primarily composed of icy materials. During the formation of the Solar System, there were probably many more (planetesimals), but they have all merged with or been destroyed by the four remaining worlds in the solar nebula. The terrestrial planets all have roughly the same structure: a central metallic core, mostly iron, with a surrounding silicate mantle. The Moon is similar, but lacks a substantial iron core. Three of the four solar terrestrial planets (Venus,
Alien Legacy of the system. The Beta Caeli system is similar to our real-life solar system, with a barren, rocky inner planet, terrestrial planets in the habitable zone of the inner system, followed by gas giants in the outer system that first increase and then decrease in size, and a tiny rock outermost. The naming of the Caelian planets closely matches that of naming planets in our solar system. But while our system uses the names of Roman deities (except for Uranus), Caeli has Greek ones; Gaea is the Greek goddess of the Earth, and Rhea is her daughter. In addition, as