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The following is a list of planet types by their mass, orbit, physical and chemical composition, or by another classification.
| | This article needs additional citations for verification .(February 2020) |
The following is a list of planet types by their mass, orbit, physical and chemical composition, or by another classification.
| Planet type | Description | Example(s) |
|---|---|---|
| Super-Jupiter | An astronomical object more massive than the planet Jupiter. | Kappa Andromedae b, Kepler-1625b |
| 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, which would make one a Mega Earth. [1] Regardless of their bulk compositions, giant planets normally have thick atmospheres of hydrogen and helium. | Jupiter |
| Super-Neptune | A planet that is more massive than the planet Neptune. These planets are generally described as being around 5–7 times as large as Earth with estimated masses of 20–80 ME; | PH1b, K2-33b |
| Neptunian planet | Planets of mass similar to Uranus or Neptune; smaller than the gas giants, but still much larger than Earth. | Gliese 436 b, GJ 3470 b |
| Sub-Neptune | a planet with smaller radius than Neptune even though it may have a larger mass | HD 110067 (b, c, d, e, f and g) |
| Mini-Neptune | Also known as a gas dwarf or transitional planet. A planet up to 10 Earth masses, but less massive than Uranus and Neptune. Mini-Neptunes 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). | HD 63433 c |
| Mega-Earth | Proposed neologism for a massive terrestrial exoplanet that is at least ten times the mass of Earth | Kepler-10c |
| Super-Earth | 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 14.5 and 17.1 Earth masses respectively. | Kepler-10b, Gliese 667 Cc |
| Sub-Earth | A classification of planets "substantially less massive" than Earth and Venus. | Mercury & Kepler-37b |
| Planet type | Description | Examples |
|---|---|---|
| Circumbinary planet | An exoplanet that orbits two stars. | PH1b, Kepler-16b |
| Circumtriple planet | An exoplanet that orbits three stars. | Gliese 900 b |
| Double planet | Also known as a binary planet. Two planetary-mass objects orbiting each other. | OGLE-2017-BLG-0380Lb [2] |
| Eccentric Jupiter | A gas giant that orbits its star in an eccentric orbit. | HD 80606 b, HD 20782 b |
| Exoplanet | A planet that does not orbit the Sun, but a different star, a stellar remnant, or a brown dwarf. | Proxima Centauri b, 51 Pegasi b |
| Extragalactic planet | An exoplanet outside the Milky Way. | M51-ULS-1b (unconfirmed) |
| Goldilocks planet | A planet with an orbit that falls within the star's habitable zone. The name derives from the fairy tale "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". | Kepler-186f, 38 Virginis b |
| Hot Jupiter | 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 AU (2.2×106 and 74.8×106 km)—to their parent stars, whereas Jupiter orbits its parent star (the Sun) at 5.2 AU (780×106 km), causing low surface temperatures. | 51 Pegasi b, HD 209458 b, KELT-9b |
| Hot Neptune | 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. | Gliese 436 b, LTT 9779 b |
| Inferior planets | Planets whose orbits lie within the orbit of Earth. [nb 1] | Mercury and Venus |
| Inner planet | A planet in the Solar System that have orbits smaller than the asteroid belt. [nb 2] | Mercury, Venus, Earth, Mars |
| Outer planet | A planet in the Solar System beyond the asteroid belt, and hence refers to the gas giants. | Jupiter, Saturn, Uranus and Neptune |
| Pulsar planet | A planet that orbits a pulsar or a rapidly rotating neutron star. | PSR B1257+12 A , B and C |
| Rogue planet | Also known as an interstellar planet. A planet that is not bound to any star, stellar remnant or brown dwarf. | OGLE-2016-BLG-1928 |
| Superior planets | Planets whose orbits lie outside the orbit of Earth. [nb 1] | Jupiter, Saturn, Uranus and Neptune |
| Trojan planet | A planet co-orbiting with another planet. The discovery of a pair of co-orbital exoplanets has been reported, but later retracted. [3] One possibility for the habitable zone is a trojan planet of a gas giant close to its star. | GJ 3470 c (unconfirmed) |
| Planet type | Description | Example |
|---|---|---|
| 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. | TOI-849b (candidate) |
| Carbon planet | A theoretical terrestrial planet that could form if protoplanetary discs are carbon-rich and oxygen-poor. | PSR B1257+12 A, B and C (candidates) |
| Coreless planet | A theoretical planet that has undergone planetary differentiation but has no metallic core. Not to be confused with the Hollow Earth concept. | |
| Desert planet | A terrestrial planet with an arid surface consistency similar to Earth's deserts. | Mars |
| Gas dwarf | A low-mass planet composed primarily of hydrogen and helium. | GJ 1214 b |
| Gas giant | A massive planet composed primarily of hydrogen and helium. | Saturn, Jupiter, 70 Virginis b |
| Helium planet | A theoretical 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. | |
| Hycean planet | A hypothetical type of habitable planet described as a hot, water-covered planet with a hydrogen-rich atmosphere. | TOI-270 d, K2-18b (candidates) |
| Ice giant | 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). | Neptune and Uranus |
| Ice planet | A theoretical planet with a solid, icy surface. | OGLE-2005-BLG-390Lb |
| Iron planet | A planet that consists primarily of an iron-rich core with little or no mantle, such as Mercury. | K2-137b, LHS 3844 b (candidates) |
| Lava planet | A theoretical terrestrial planet with a surface mostly or entirely covered by molten lava. | Kepler-10b, Kepler-78b |
| Ocean planet | A theoretical planet which has a substantial fraction of its mass made of water. | Earth, Kepler-22b (candidate) |
| Protoplanet | A large planetary embryo that originates within protoplanetary discs and has undergone internal melting to produce differentiated interiors. Protoplanets are believed to form out of kilometer-sized planetesimals that attract each other gravitationally and collide. | PDS 70 b and c, AB Aurigae b |
| Puffy planet | A gas giant with a large radius and very low density which is similar to or lower than Saturn's. | TrES-4 |
| Super-puff | A type of exoplanet with a mass only a few times larger than Earth's but with a radius larger than that of Neptune, giving it a very low mean density. | Kepler-51b, c and d |
| Silicate planet | A terrestrial planet that is composed primarily of silicate rocks. All four inner planets in the Solar System are silicon-based. | Mercury, Venus, Earth and Mars |
| Terrestrial planet | Also known as a telluric planet or rocky planet. A planet that is composed primarily of carbonaceous or silicate rocks or metals. | Solar System inner planets, TRAPPIST-1b, Kepler-37b |
| Planet type | Description | Example |
|---|---|---|
| Classical planets | The planets as known during classical antiquity: the Moon, the Sun, Mercury, Venus, Mars, Jupiter, and Saturn. | |
| Earth analog | A planet or even a superhabitable planet with conditions to be compared with those found on Earth. | Teegarden b and c, KOI-4878.01 (unconfirmed) |
| Jupiter analog | A planet whose physical and orbital characteristics are comparable to those of Jupiter. | HIP 11915 b |
| Hypothetical planet | A planet or similar body whose existence is not proven, but is believed by some to exist. | KOI-4878.01, FU Orionis Ab |
A planet is a large, rounded astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets by the most restrictive definition of the term: the terrestrial planets Mercury, Venus, Earth, and Mars, and the giant planets Jupiter, Saturn, Uranus, and Neptune. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young protostar orbited by a protoplanetary disk. Planets grow in this disk by the gradual accumulation of material driven by gravity, a process called accretion.
The Solar System is the gravitationally bound system of the Sun and the objects that orbit it. It formed about 4.6 billion years ago when a dense region of a molecular cloud collapsed, forming the Sun and a protoplanetary disc. The Sun is a typical star that maintains a balanced equilibrium by the fusion of hydrogen into helium at its core, releasing this energy from its outer photosphere. Astronomers classify it as a G-type main-sequence star.
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. Among astronomers who use the geophysical definition of a planet, two or three planetary-mass satellites – Earth's Moon, Io, and sometimes Europa – may also be considered terrestrial planets. The large rocky asteroids Pallas and Vesta are sometimes included as well, albeit rarely. The terms "terrestrial planet" and "telluric planet" are derived from Latin words for Earth, as these planets are, in terms of structure, Earth-like. Terrestrial planets are generally studied by geologists, astronomers, and geophysicists.
In the Solar System, a planet is said to be inferior or interior with respect to another planet if its orbit lies inside the other planet's orbit around the Sun. In this situation, the latter planet is said to be superior to the former. In the reference frame of the Earth, where the terms were originally used, the inferior planets are Mercury and Venus, while the superior planets are Mars, Jupiter, Saturn, Uranus and Neptune. Dwarf planets like Ceres or Pluto and most asteroids are 'superior' in the sense that they almost all orbit outside the orbit of Earth.
In astronomy, a transit is the passage of a celestial body directly between a larger body and the observer. As viewed from a particular vantage point, the transiting body appears to move across the face of the larger body, covering a small portion of it.
A planetary system is a set of gravitationally bound non-stellar bodies in or out of orbit around a star or star system. Generally speaking, systems with one or more planets constitute a planetary system, although such systems may also consist of bodies such as dwarf planets, asteroids, natural satellites, meteoroids, comets, planetesimals and circumstellar disks. For example, the Sun together with the planetary system revolving around it, including Earth, form the Solar System. The term exoplanetary system is sometimes used in reference to other planetary systems.
In astronomy and astrobiology, the habitable zone (HZ), or more precisely the circumstellar habitable zone (CHZ), is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure. The bounds of the HZ are based on Earth's position in the Solar System and the amount of radiant energy it receives from the Sun. Due to the importance of liquid water to Earth's biosphere, the nature of the HZ and the objects within it may be instrumental in determining the scope and distribution of planets capable of supporting Earth-like extraterrestrial life and intelligence.
Planetary habitability is the measure of a planet's or a natural satellite's potential to develop and maintain an environment hospitable to life. Life may be generated directly on a planet or satellite endogenously. Research suggests that life may also be transferred from one body to another, through a hypothetical process known as panspermia. Environments do not need to contain life to be considered habitable nor are accepted habitable zones (HZ) the only areas in which life might arise.
There is evidence that the formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a protoplanetary disk out of which the planets, moons, asteroids, and other small Solar System bodies formed.
A Super-Earth or super-terran or super-tellurian is a type of exoplanet with a mass higher than Earth, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17.1 times Earth's, respectively. The term "super-Earth" refers only to the mass of the planet, and so does not imply anything about the surface conditions or habitability. The alternative term "gas dwarfs" may be more accurate for those at the higher end of the mass scale, although "mini-Neptunes" is a more common term.
The following outline is provided as an overview of and topical guide to the Solar System:
In planetary astronomy, the grand tack hypothesis proposes that Jupiter formed at a distance of 3.5 AU from the Sun, then migrated inward to 1.5 AU, before reversing course due to capturing Saturn in an orbital resonance, eventually halting near its current orbit at 5.2 AU. The reversal of Jupiter's planetary migration is likened to the path of a sailboat changing directions (tacking) as it travels against the wind.
Wolf 1061 c is an exoplanet orbiting within the habitable zone of the red dwarf star Wolf 1061 in the constellation Ophiuchus, about 14.1 light-years from Earth. At the time of discovery, it was the closest known potentially habitable exoplanet to Earth, though several closer ones have since been found. It is the second planet in order from its host star in a triple planetary system, and has an orbital period of 17.9 days. Wolf 1061 c is classified as a super-Earth exoplanet as its mass is between that of Earth and the ice giants.
Tau Ceti f is a potential super-Earth or mini-Neptune orbiting Tau Ceti that was discovered in 2012 by statistical analyses of the star's variations in radial velocity, based on data obtained using HIRES, AAPS, and HARPS. It is of interest because its orbit places it in Tau Ceti's extended habitable zone, but a 2015 study implies that there may not be a detectable biosignature because it has only been in the temperate zone for less than one billion years. In 2017, it was again recovered from radial-velocity data, along with Tau Ceti e. Despite this, it remains an unconfirmed candidate.
Over the years, our ability to detect, confirm, and characterize exoplanets and their atmospheres has improved, allowing researchers to begin constraining exoplanet interior composition and structure. While most exoplanet science is focused on exoplanetary atmospheric environments, the mass and radius of a planet can tell us about a planet's density, and hence, its internal processes. The internal processes of a planet are partly responsible for its atmosphere, and so they are also a determining factor in a planet's capacity to support life.
Habitability of yellow dwarf systems defines the suitability for life of exoplanets belonging to yellow dwarf stars. These systems are the object of study among the scientific community because they are considered the most suitable for harboring living organisms, together with those belonging to K-type stars.
Solar System belts are asteroid and comet belts that orbit the Sun in the Solar System in interplanetary space. The Solar System belts' size and placement are mostly a result of the Solar System having four giant planets: Jupiter, Saturn, Uranus and Neptune far from the sun. The giant planets must be in the correct place, not too close or too far from the sun for a system to have Solar System belts.
