List of planet types
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The following is a list of planet types:
- Chthonian planet – An extrasolar planet that orbits close to its parent star. Most Chthonian planets are expected to be gas giants that had their atmospheres stripped away, leaving their cores.
- Carbon planet – A theoretical type of terrestrial planet that could form if protoplanetary discs are carbon-rich and oxygen-poor.
- Circumbinary planet – An exoplanet that orbits two stars.
- Coreless planet – A theoretical type of planet that has undergone planetary differentiation but has no metallic core. It is not the same as a hollow Earth.
- Desert planet – A theoretical type of terrestrial planet with very little water.
- Dwarf planet – A celestial body in direct orbit of the Sun that is massive enough for its shape to be controlled by gravity, but that has not cleared its orbit of other objects.
- Earth analog – A planet with environmental conditions similar to those found on Earth.
- Eccentric Jupiter – A gas giant that orbits its star in an eccentric orbit.
- Exoplanet – A planet that does not orbit the Sun, but a different star, a stellar remnant, or a brown dwarf.
- Extragalactic planet – An exoplanet outside the Milky Way.
- Gas dwarf – A low-mass planet composed primarily of hydrogen and helium.
- Gas giant – A massive planet composed primarily of hydrogen and helium.
- Giant planet – A massive planet. They are most commonly composed primarily of 'gas' (hydrogen and helium) or 'ices' (volatiles such as water, methane, and ammonia), but may also be composed primarily of rock. Regardless of their bulk compositions, giant planets normally have thick atmospheres of hydrogen and helium.
- Goldilocks planet - A Goldilocks planet is a planet that falls within a star's habitable zone, and the name is often specifically used for planets close to the size of Earth. The name comes from the children's fairy tale of Goldilocks and the Three Bears, in which a little girl chooses from sets of three items, ignoring the ones that are too extreme (large or small, hot or cold, etc.), and settling on the one in the middle, which is "just right".
- Helium planet - A helium planet is a theoretical type of planet that may form via mass loss from a low-mass white dwarf. Helium planets are predicted to have roughly the same diameter as hydrogen–helium planets of the same mass.
- Hot Jupiter - Hot Jupiters are a class of extrasolar planets whose characteristics are similar to Jupiter, but that have high surface temperatures because they orbit very close—between approximately 0.015 and 0.5 astronomical units (2.2×106 and 74.8×106 km)—to their parent stars, whereas Jupiter orbits its parent star (the Sun) at 5.2 astronomical units (780×106 km), causing low surface temperatures.
- Hot Neptune - A hot Neptune is an extrasolar planet in an orbit close to its star (normally less than one astronomical unit away), with a mass similar to that of Uranus or Neptune.
- Hypothetical planet - A hypothetical planet or hypothetical planetary object is a planet or similar body whose existence is not proven, but is believed by some to exist.
- Ice giant - An ice giant is a giant planet composed mainly of 'ices'—volatile substances heavier than hydrogen and helium, such as water, methane, and ammonia—as opposed to 'gas' (hydrogen and helium).
- Ice planet - An ice planet is a type of planet with an icy surface. Ice planets consist of a global cryosphere. Ice planets are bigger versions of Solar System's icy moons such as Europa, Enceladus, and Triton; dwarf planets Pluto and Eris, and many other icy Solar System bodies.
- Inferior and superior planets - The planets whose orbits lie within the orbits of Earth are called Inferior planets whereas the planets whose orbits lie outside the orbit of Earth are called superior planets. The terms "inferior planet" and "superior planet" were originally used in the geocentric cosmology of Claudius Ptolemy to differentiate as 'inferior' those planets (Mercury and Venus) whose epicycle remained collinear with Earth and the Sun, compared to the 'superior' planets (Mars, Jupiter, and Saturn) that did not.
- Inner planet - The four inner or terrestrial planets have dense, rocky compositions, few or no moons, and no ring systems. They are composed largely of refractory minerals, such as the silicates, which form their crusts and mantles, and metals, such as iron and nickel, which form their cores. Three of the four inner planets (Venus, Earth and Mars) have atmospheres substantial enough to generate weather; all have impact craters and tectonic surface features, such as rift valleys and volcanos. The term inner planet should not be confused with inferior planet, which designates those planets that are closer to the Sun than Earth is (i.e. Mercury and Venus).
- Iron planet - An iron planet is a type of planet that consists primarily of an iron-rich core with little or no mantle.
- Lava planet - A lava planet is a hypothetical type of terrestrial planet, with a surface mostly or entirely covered by molten lava. Situations where such planets could exist include a young terrestrial planet just after its formation, a planet that has recently suffered a large collision event, or a planet orbiting very close to its star, causing intense irradiation and tidal forces.
- Mesoplanet - Mesoplanets are planetary bodies with sizes smaller than Mercury but larger than Ceres. The term was coined by Isaac Asimov. Assuming "size" is defined by linear dimension (or by volume), mesoplanets should be approximately 1,000 km to 5,000 km in diameter.
- Mini-Neptune - A mini-Neptune (sometimes known as a gas dwarf or transitional planet) is a planet smaller than Uranus and Neptune, up to 10 Earth masses. Those planets have thick hydrogen–helium atmospheres, probably with deep layers of ice, rock or liquid oceans (made of water, ammonia, a mixture of both, or heavier volatiles).
- Ocean planet - An ocean planet (also termed a waterworld) is a hypothetical type of planet which has a substantial fraction of its mass made of water.
- Outer planet - The outer planets are those planets in the Solar System beyond the asteroid belt, and hence refers to the gas giants.
- Planetar - A planetar is a type of extrasolar planet.
In astronomy, the term planetar has been used to denote two different kinds of celestial objects:
- Brown dwarfs—objects with a size larger than planets but smaller than stars, having formed by processes that typically yield planets; and
- Sub-brown dwarfs—objects smaller than brown dwarfs that do not orbit a star.
- Protoplanet - Protoplanets are large planetary embryos that originate within protoplanetary discs and have undergone internal melting to produce differentiated interiors. They are believed to form out of kilometer-sized planetesimals that attract each other gravitationally and collide.
- Puffy planet - Gas giants with a large radius and very low density are sometimes called "puffy planets" or "hot Saturns", due to their density similar to Saturn's.
- Pulsar planet - Pulsar planets are planets that are found orbiting pulsars, or rapidly rotating neutron stars.
- Rogue planet - A rogue planet is a planetary-mass object that orbits the galaxy directly.
- Sub-Earth - Sub-Earth is a classification of planets "substantially less massive" than Earth and Venus.
- Super-Earth - A super-Earth is an extrasolar planet with a mass higher than Earth's, but substantially below the mass of the Solar System's smaller gas giants Uranus and Neptune, which are 15 and 17 Earth masses respectively.
- Super-Jupiter - A super-Jupiter is an astronomical object that's more massive than the planet Jupiter.
- Terrestrial planet - A terrestrial planet, telluric planet or rocky planet is a planet that is composed primarily of silicate rocks or metals.
- Trojan planet - The discovery of a pair of co-orbital exoplanets has been reported but later retracted.One possibility for the habitable zone is a trojan planet of a gas giant close to its star.
- Planet types in science fiction
- Class M planet
- Planet classifications in the Star Trek series
- Types of planets in Noctis
- Sudarsky's gas giant classification
- Hypothetical planet types
- Stellar classification
- Substellar object
- Sub-brown dwarf
- Dwarf planet
- Minor planet
- Centaur (minor planet)
- Periodic Table of Exoplanets at Planetary Habitability Laboratory, University of Puerto Rico at Arecibo
- A Thermal Planetary Habitability Classification for Exoplanets
- A Mass Classification for both Solar and Extrasolar Planets
- What Kinds of Planets Are Out There? at NASA
- Stern and Levison, "Regarding the criteria for planethood and proposed planetary classification schemes," Highlights of Astronomy 12 (2002)
- Lineweaver, C. H. and Robles, J. A. (2006). Towards a Classification System of Terrestrial Planets
- Out There: A Strange Zoo of Other Worlds
- SpaceEngine Planet Classifications
- A Planetary Classification Proposal