page_title: Geology of solar terrestrial planets
hierarchical_section_title: Geology of solar terrestrial planets
caption_attribution_description: Size comparison of the four terrestrial planets Mercury, Venus, Earth and Mars and the terrestrial dwarf planet Ceres.
context_page_description: The geology of solar terrestrial planets mainly deals with the geological aspects of the four terrestrial planets of the Solar System – Mercury, Venus, Earth, and Mars – and one terrestrial dwarf planet: Ceres. Earth is the only terrestrial planet known to have an active hydrosphere.
  Terrestrial planets are substantially different from the giant planets, which might not have solid surfaces and are composed mostly of some combination of hydrogen, helium, and water existing in various physical states. Terrestrial planets have a compact, rocky surfaces, and Venus, Earth, and Mars each also have an atmosphere. Their size, radius, and density are all similar.
  Terrestrial planets have numerous similarities to plutoids, 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, 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.
context_section_description: The geology of solar terrestrial planets mainly deals with the geological aspects of the four terrestrial planets of the Solar System – Mercury, Venus, Earth, and Mars – and one terrestrial dwarf planet: Ceres. Earth is the only terrestrial planet known to have an active hydrosphere.
  Terrestrial planets are substantially different from the giant planets, which might not have solid surfaces and are composed mostly of some combination of hydrogen, helium, and water existing in various physical states. Terrestrial planets have a compact, rocky surfaces, and Venus, Earth, and Mars each also have 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 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, 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 refers to any planet that is closer to the Sun than the observer's planet is, but usually refers to Mercury and Venus.
caption: The inner planets. From left to right: Mercury, Venus, Earth, Mars and terrestrial dwarf planet, Ceres (sizes to scale)
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