Geology of solar terrestrial planets Geology of solar terrestrial planets 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.
Retrograde and prograde motion relative to the Sun except those of Uranus. If there is a collision, material could be ejected in any direction and coalesce into either prograde or retrograde moons, which may be the case for the moons of dwarf planet Haumea, although Haumea's rotation direction is not known. Asteroids usually have a prograde orbit around the Sun. Only a few dozen asteroids in retrograde orbits are known. Some asteroids with retrograde orbits may be burnt-out comets, but some may acquire their retrograde orbit due to gravitational interactions with Jupiter. Due to their small size and their large distance from Earth it