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A terrestrial planet, tellurian planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate, rocks or metals. Within the Solar System , the terrestrial planets accepted by the IAU are the inner planets closest to the Sun : Mercury , Venus , Earth and Mars .
The four inner or terrestrial planets have dense, rocky compositions, few or no moons, and no ring systems. They are composed largely of minerals with high melting points, such as the silicates which form their solid crusts and semi-liquid mantles , and metals such as iron and nickel , which form their cores .
All of the rocky inner planets, as well as the moon, have an iron-dominant core. Venus and Mars have an additional major element in the core. Venus’ core is believed to be iron-nickel, similarly to Earth. Mars, on the other hand, is believed to have an iron-sulfur core and is separated into an outer liquid layer around an inner solid core. [20]
The outer planets Jupiter, Saturn, Uranus and Neptune, compared to the inner planets Earth, Venus, Mars, and Mercury at the bottom right The four outer planets, called giant planets or Jovian planets, collectively make up 99% of the mass orbiting the Sun. [ h ] All four giant planets have multiple moons and a ring system, although only Saturn's ...
Planets whose orbits lie within the orbit of Earth. [nb 1] Inner planet: A planet in the Solar System that have orbits smaller than the asteroid belt. [nb 2] Outer planet: A planet in the Solar System beyond the asteroid belt, and hence refers to the gas giants. Pulsar planet: A planet that orbits a pulsar or a rapidly rotating neutron star ...
However, smaller gas planets and planets closer to their star will lose atmospheric mass more quickly via hydrodynamic escape than larger planets and planets farther out. [12] [13] A gas dwarf could be defined as a planet with a rocky core that has accumulated a thick envelope of hydrogen, helium and other volatiles, having as result a total ...
According to the solar nebular disk model, rocky planets form in the inner part of the protoplanetary disk, within the frost line, where the temperature is high enough to prevent condensation of water ice and other substances into grains. [64] This results in coagulation of purely rocky grains and later in the formation of rocky planetesimals.
Planetary surfaces are found throughout the Solar System, from the inner terrestrial planets, to the asteroid belt, the natural satellites of the giant planets and beyond to the Trans-Neptunian objects. Surface conditions, temperatures and terrain vary significantly due to a number of factors including Albedo often generated by the surfaces itself