The geology of solar terrestrial planets mainly deals with the geological aspects of four planets of the Solar System namely, Mercury, Venus, Earth, and Mars and one terrestrial dwarf planet, Ceres. Only one terrestrial planet, Earth, is known to have an active hydrosphere.
Terrestrial planets are substantially different from gas giants, which might not have solid surfaces and are composed mostly of some combination of hydrogen, helium, and water existing in various physical states. These planets have a compact, rocky surfaces, with the last three also having an atmosphere. 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 composed of more 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.
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 an iron core. Three of the four solar terrestrial planets (Venus, Earth and Mars) have substantial atmospheres; all have impact craters and tectonic surface features such as rift valleys and volcanoes. The term inner planet should not be confused with inferior planet, which designates those planets which are closer to the Sun than Earth is (i.e. Mercury and Venus).
Read more about Geology Of Solar Terrestrial Planets: Formation of Solar Planets, Surface Geology of Inner Solar Planets, Small Solar System Bodies
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“The solar system has no anxiety about its reputation, and the credit of truth and honesty is as safe; nor have I any fear that a skeptical bias can be given by leaning hard on the sides of fate, of practical power, or of trade, which the doctrine of Faith cannot down-weigh.”
—Ralph Waldo Emerson (1803–1882)
“Perhaps when distant people on other planets pick up some wave-length of ours all they hear is a continuous scream.”
—Iris Murdoch (b. 1919)