The eight planets of the Solar System with size to scale (up to down, left to right): Saturn, Jupiter, Uranus, Neptune (outer planets), Earth, Venus, Mars, and Mercury (inner planets)

A planet is a large, rounded astronomical body that is neither a star nor its remnant. 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 has at least eight planets: the terrestrial planets Mercury, Venus, Earth and Mars, and the giant planets Jupiter, Saturn, Uranus and Neptune. These planets each rotate around an axis tilted with respect to its orbital pole. All planets of the Solar System other than Mercury possess a considerable atmosphere, and some share such features as ice caps, seasons, volcanism, hurricanes, tectonics, and even hydrology. Apart from Venus and Mars, the Solar System planets generate magnetic fields, and all except Venus and Mercury have natural satellites. The giant planets bear planetary rings, the most prominent being those of Saturn.

The word planet probably comes from the Greek planḗtai, meaning "wanderers". In antiquity, this word referred to the Sun, Moon, and five points of light visible by the naked eye that moved across the background of the stars—namely, Mercury, Venus, Mars, Jupiter and Saturn. Planets have historically had religious associations: multiple cultures identified celestial bodies with gods, and these connections with mythology and folklore persist in the schemes for naming newly discovered Solar System bodies. Earth itself was recognized as a planet when heliocentrism supplanted geocentrism during the 16th and 17th centuries.

With the development of the telescope, the meaning of planet broadened to include objects only visible with assistance: the moons of the planets beyond Earth; the ice giants Uranus and Neptune; Ceres and other bodies later recognized to be part of the asteroid belt; and Pluto, later found to be the largest member of the collection of icy bodies known as the Kuiper belt. The discovery of other large objects in the Kuiper belt, particularly Eris, spurred debate about how exactly to define a planet. The International Astronomical Union (IAU) adopted a standard by which the four terrestrials and four giants qualify, placing Ceres, Pluto and Eris in the category of dwarf planet,[1][2][3] although many planetary scientists have continued to apply the term planet more broadly.[4]

Further advances in astronomy led to the discovery of over five thousand planets outside the Solar System, termed exoplanets. These include hot Jupiters—giant planets that orbit close to their parent stars—like 51 Pegasi b, super-Earths like Gliese 581c that have masses in between that of Earth and Neptune; and planets smaller than Earth, like Kepler-20e. Multiple exoplanets have been found to orbit in the habitable zones of their stars, but Earth remains the only planet known to support life.


Further information: History of astronomy and Timeline of Solar System astronomy

1660 illustration of Claudius Ptolemy's geocentric model

The idea of planets has evolved over its history, from the divine lights of antiquity to the earthly objects of the scientific age. The concept has expanded to include worlds not only in the Solar System, but in multitudes of other extrasolar systems. The consensus definition as to what counts as a planet vs. other objects orbiting the Sun has changed several times, previously encompassing asteroids, moons, and dwarf planets like Pluto,[5][6][7] and there continues to be some disagreement today.[7]

The five classical planets of the Solar System, being visible to the naked eye, have been known since ancient times and have had a significant impact on mythology, religious cosmology, and ancient astronomy. In ancient times, astronomers noted how certain lights moved across the sky, as opposed to the "fixed stars", which maintained a constant relative position in the sky.[8] Ancient Greeks called these lights πλάνητες ἀστέρες (planētes asteres, "wandering stars") or simply πλανῆται (planētai, "wanderers"),[9] from which today's word "planet" was derived.[10][11][12] In ancient Greece, China, Babylon, and indeed all pre-modern civilizations,[13][14] it was almost universally believed that Earth was the center of the Universe and that all the "planets" circled Earth. The reasons for this perception were that stars and planets appeared to revolve around Earth each day[15] and the apparently common-sense perceptions that Earth was solid and stable and that it was not moving but at rest.[16]


Main article: Babylonian astronomy

The first civilization known to have a functional theory of the planets were the Babylonians, who lived in Mesopotamia in the first and second millennia BC. The oldest surviving planetary astronomical text is the Babylonian Venus tablet of Ammisaduqa, a 7th-century BC copy of a list of observations of the motions of the planet Venus, that probably dates as early as the second millennium BC.[17] The MUL.APIN is a pair of cuneiform tablets dating from the 7th century BC that lays out the motions of the Sun, Moon, and planets over the course of the year.[18] Late Babylonian astronomy is the origin of Western astronomy and indeed all Western efforts in the exact sciences.[19] The Enuma anu enlil, written during the Neo-Assyrian period in the 7th century BC,[20] comprises a list of omens and their relationships with various celestial phenomena including the motions of the planets.[21][22] Venus, Mercury, and the outer planets Mars, Jupiter, and Saturn were all identified by Babylonian astronomers. These would remain the only known planets until the invention of the telescope in early modern times.[23]

Greco-Roman astronomy

See also: Greek astronomy

The ancient Greeks initially did not attach as much significance to the planets as the Babylonians. In the 6th and 5th centuries BC, the Pythagoreans appear to have developed their own independent planetary theory, which consisted of the Earth, Sun, Moon, and planets revolving around a "Central Fire" at the center of the Universe. Pythagoras or Parmenides is said to have been the first to identify the evening star (Hesperos) and morning star (Phosphoros) as one and the same (Aphrodite, Greek corresponding to Latin Venus),[24] though this had long been known in Mesopotamia.[25][26] In the 3rd century BC, Aristarchus of Samos proposed a heliocentric system, according to which Earth and the planets revolved around the Sun. The geocentric system remained dominant until the Scientific Revolution.[16]

By the 1st century BC, during the Hellenistic period, the Greeks had begun to develop their own mathematical schemes for predicting the positions of the planets. These schemes, which were based on geometry rather than the arithmetic of the Babylonians, would eventually eclipse the Babylonians' theories in complexity and comprehensiveness, and account for most of the astronomical movements observed from Earth with the naked eye. These theories would reach their fullest expression in the Almagest written by Ptolemy in the 2nd century CE. So complete was the domination of Ptolemy's model that it superseded all previous works on astronomy and remained the definitive astronomical text in the Western world for 13 centuries.[17][27] To the Greeks and Romans there were seven known planets, each presumed to be circling Earth according to the complex laws laid out by Ptolemy. They were, in increasing order from Earth (in Ptolemy's order and using modern names): the Moon, Mercury, Venus, the Sun, Mars, Jupiter, and Saturn.[12][27][28]

Medieval astronomy

Main articles: Astronomy in the medieval Islamic world and Indian astronomy

After the fall of the Western Roman Empire, astronomy developed further in India and the medieval Islamic world. In 499 CE, the Indian astronomer Aryabhata propounded a planetary model that explicitly incorporated Earth's rotation about its axis, which he explains as the cause of what appears to be an apparent westward motion of the stars. He also theorised that the orbits of planets were elliptical.[29] Aryabhata's followers were particularly strong in South India, where his principles of the diurnal rotation of Earth, among others, were followed and a number of secondary works were based on them.[30]

The astronomy of the Islamic Golden Age mostly took place in the Middle East, Central Asia, Al-Andalus, and North Africa, and later in the Far East and India. These astronomers, like the polymath Ibn al-Haytham, generally accepted geocentrism, although they did dispute Ptolemy's system of epicycles and sought alternatives. The 10th-century astronomer Abu Sa'id al-Sijzi accepted that the Earth rotates around its axis.[31] In the 11th century, the transit of Venus was observed by Avicenna.[32] His contemporary Al-Biruni devised a method of determining the Earth's radius using trigonometry that, unlike the older method of Eratosthenes, only required observations at a single mountain.[33]

Scientific Revolution and new planets

See also: Heliocentrism

With the advent of the Scientific Revolution and the heliocentric model of Copernicus, Galileo and Kepler, use of the term "planet" changed from something that moved around the sky relative to the fixed star to a body that orbited the Sun, directly (a primary planet) or indirectly (a secondary or satellite planet). Thus the Earth was added to the roster of planets[34] and the Sun was removed. The Copernican count of primary planets stood until 1781, when William Herschel discovered Uranus.[35]

When four satellites of Jupiter (the Galilean moons) and five of Saturn were discovered in the 17th century, they were thought of as "satellite planets" or "secondary planets" orbiting the primary planets, though in the following decades they would come to be called simply "satellites" for short. Scientists generally considered planetary satellites to also be planets until about the 1920s, although this usage was not common among non-scientists.[7]

In the first decade of the 19th century, four new planets were discovered: Ceres (in 1801), Pallas (in 1802), Juno (in 1804), and Vesta (in 1807). It soon became apparent that they were rather different from previously known planets: they shared the same general region of space, between Mars and Jupiter (the asteroid belt), with sometimes overlapping orbits. This was an area where only one planet had been expected, and they were much much smaller than all other planets; indeed, it was suspected that they might be shards of a larger planet that had broken up. Herschel called them asteroids (from the Greek for "starlike") because even in the largest telescopes they resembled stars, without a resolvable disk.[6][36]

The situation was stable for four decades, but in the mid-1840s several additional asteroids were discovered (Astraea in 1845, Hebe and Iris in 1847, Flora and Metis in 1848, and Hygiea in 1849). New "planets" were discovered every year; as a result, astronomers began tabulating the asteroids (minor planets) separately from the major planets, and assigning them numbers instead of abstract planetary symbols,[6] although they continued to be considered as small planets.[37]

Neptune was discovered in 1846, its position having been predicted thanks to its gravitational influence upon Uranus. Because the orbit of Mercury appeared to be affected in a similar way, it was believed in the late 19th century that there might be another planet even closer to the Sun. However, the discrepancy between Mercury's orbit and the predictions of Newtonian gravity was instead explained by an improved theory of gravity, Einstein's general relativity.[38][39]

20th century

Pluto was discovered in 1930. After initial observations led to the belief that it was larger than Earth,[40] the object was immediately accepted as the ninth major planet. Further monitoring found the body was actually much smaller: in 1936, Ray Lyttleton suggested that Pluto may be an escaped satellite of Neptune,[41] and Fred Whipple suggested in 1964 that Pluto may be a comet.[42] The discovery of its large moon Charon in 1978 showed that Pluto was only 0.2% the mass of Earth.[43] As this was still substantially more massive than any known asteroid, and because no other trans-Neptunian objects had been discovered at that time, Pluto kept its planetary status, only officially losing it in 2006.[44][45]

In the 1950s, Gerard Kuiper published papers on the origin of the asteroids. He recognised that asteroids were typically not spherical, as had previously been thought, and that the asteroid families were remnants of collisions. Thus he differentiated between the largest asteroids as "true planets" versus the smaller ones as collisional fragments. From the 1960s onwards, the term "minor planet" was mostly displaced by the term "asteroid", and references to the asteroids as planets in the literature became scarce, except for the geologically evolved largest three: Ceres, and less often Pallas and Vesta.[37]

The beginning of Solar System exploration by space probes in the 1960s spurred a renewed interest in planetary science. A split in definitions regarding satellites occurred around then: planetary scientists began to reconsider the large moons as also being planets, but astronomers who were not planetary scientists generally did not.[7]

In 1992, astronomers Aleksander Wolszczan and Dale Frail announced the discovery of planets around a pulsar, PSR B1257+12.[46] This discovery is generally considered to be the first definitive detection of a planetary system around another star. Then, on 6 October 1995, Michel Mayor and Didier Queloz of the Geneva Observatory announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[47]

The discovery of extrasolar planets led to another ambiguity in defining a planet: the point at which a planet becomes a star. Many known extrasolar planets are many times the mass of Jupiter, approaching that of stellar objects known as brown dwarfs. Brown dwarfs are generally considered stars due to their theoretical ability to fuse deuterium, a heavier isotope of hydrogen. Although objects more massive than 75 times that of Jupiter fuse simple hydrogen, objects of 13 Jupiter masses can fuse deuterium. Deuterium is quite rare, constituting less than 0.0026% of the hydrogen in the galaxy, and most brown dwarfs would have ceased fusing deuterium long before their discovery, making them effectively indistinguishable from supermassive planets.[48]

21st century

With the discovery during the latter half of the 20th century of more objects within the Solar System and large objects around other stars, disputes arose over what should constitute a planet. There were particular disagreements over whether an object should be considered a planet if it was part of a distinct population such as a belt, or if it was large enough to generate energy by the thermonuclear fusion of deuterium.[49] Complicating the matter even further, bodies too small to generate energy by fusing deuterium can form by gas-cloud collapse just like stars and brown dwarfs, even down to the mass of Jupiter:[50] there was thus disagreement about whether how a body formed should be taken into account.[49]

A growing number of astronomers argued for Pluto to be declassified as a planet, because many similar objects approaching its size had been found in the same region of the Solar System (the Kuiper belt) during the 1990s and early 2000s. Pluto was found to be just one small body in a population of thousands.[49] They often referred to the demotion of the asteroids as a precedent, although that had been done based on their geophysical differences from planets rather than their being in a belt.[7] Some of the larger trans-Neptunian objects, such as Quaoar, Sedna, Eris, and Haumea,[51] were heralded in the popular press as the tenth planet. The announcement of Eris in 2005, an object 27% more massive than Pluto, created the impetus for an official definition of a planet,[49] as considering Pluto a planet would logically have demanded that Eris be considered a planet as well. Since different procedures were in place for naming planets versus non-planets, this created an urgent situation because under the rules Eris could not be named without defining what a planet was.[7] At the time, it was also thought that the size required for a trans-Neptunian object to become round was about the same as that required for the moons of the giant planets (about 400 km diameter), a figure that would have suggested about 200 round objects in the Kuiper belt and thousands more beyond.[52][53] Many astronomers argued that the public would not accept a definition creating a large number of planets.[7]

To acknowledge the problem, the IAU set about creating the definition of planet, and produced one in August 2006. Their definition dropped to the eight significantly larger bodies that had cleared their orbit (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune), and a new class of dwarf planets was created, initially containing three objects (Ceres, Pluto and Eris).[54]

This definition has not been universally used or accepted. In planetary geology celestial objects have been assessed and defined as planets by geophysical characteristics. Planetary scientists are more interested in planetary geology than dynamics, so they classify planets based on their geological properties. A celestial body may acquire a dynamic (planetary) geology at approximately the mass required for its mantle to become plastic under its own weight. This leads to a state of hydrostatic equilibrium where the body acquires a stable, round shape, which is adopted as the hallmark of planethood by geophysical definitions. For example:[55]

a substellar-mass body that has never undergone nuclear fusion and has enough gravitation to be round due to hydrostatic equilibrium, regardless of its orbital parameters.[56]

In the Solar System, this mass is generally less than the mass required for a body to clear its orbit, and thus some objects that are considered "planets" under geophysical definitions are not considered as such under the IAU definition, such as Ceres and Pluto.[3] Proponents of such definitions often argue that location should not matter and that planethood should be defined by the intrinsic properties of an object.[3] Dwarf planets had been proposed as a category of small planet (as opposed to planetoids as sub-planetary objects) and planetary geologists continue to treat them as planets despite the IAU definition.[57]

The largest known trans-Neptunian objects with their moons; the Earth and Moon have been added for comparison. All pictures are artist's impressions except for the Pluto and Earth systems.

The number of dwarf planets even among known objects is not certain. In 2019, Grundy et al. argued based on the low densities of some mid-sized trans-Neptunian objects that the limiting size required for a trans-Neptunian object to reach equilibrium was in fact much larger than it is for the icy moons of the giant planets, being about 900 km diameter.[57] There is general consensus on Ceres in the asteroid belt[58] and on the eight trans-Neptunians that probably cross this threshold: Quaoar, Sedna, Orcus, Pluto, Haumea, Eris, Makemake, and Gonggong.[59] Planetary geologists may include the nineteen known planetary-mass moons as "satellite planets", including Earth's Moon and Pluto's Charon, like the early modern astronomers.[3][60] Some go even further and include as planets relatively large, geologically evolved bodies that are nonetheless not very round today, such as Pallas and Vesta,[3] or rounded bodies that were completely disrupted by impacts and re-accreted like Hygiea.[61][62][63]

The 2006 IAU definition presents some challenges for exoplanets because the language is specific to the Solar System and the criteria of roundness and orbital zone clearance are not presently observable for exoplanets.[64] There is no official definition of exoplanets, but the IAU's working group on the topic adopted a provisional statement in 2018.

Astronomer Jean-Luc Margot proposed a mathematical criterion that determines whether an object can clear its orbit during the lifetime of its host star, based on the mass of the planet, its semimajor axis, and the mass of its host star.[65] The formula produces a value called π that is greater than 1 for planets.[a] The eight known planets and all known exoplanets have π values above 100, while Ceres, Pluto, and Eris have π values of 0.1, or less. Objects with π values of 1 or more are expected to be approximately spherical, so that objects that fulfill the orbital-zone clearance requirement around Sun-like stars will also fulfill the roundness requirement.[66]

Definition and similar concepts

Main articles: Definition of planet and IAU definition of planet

Euler diagram showing the IAU Executive Committee conception of the types of bodies in the Solar System

At the 2006 meeting of the IAU's General Assembly, after much debate and one failed proposal, the following definition was passed in a resolution voted for by a large majority of those remaining at the meeting, addressing particularly the issue of the lower limits for a celestial object to be defined as a planet. The 2006 resolution defines planets within the Solar System as follows:[1]

A "planet" [1] is a celestial body inside the Solar System that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

[1] The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Under this definition, the Solar System is considered to have eight planets. Bodies that fulfill the first two conditions but not the third are classified as dwarf planets, provided they are not natural satellites of other planets. Originally an IAU committee had proposed a definition that would have included a larger number of planets as it did not include (c) as a criterion.[67] After much discussion, it was decided via a vote that those bodies should instead be classified as dwarf planets.[45]

This definition is based in modern theories of planetary formation, in which planetary embryos initially clear their orbital neighborhood of other smaller objects. As described below, planets form by material accreting together in a disk of matter surrounding a protostar. This process results in a collection of relatively substantial objects, each of which has either "swept up" or scattered away most of the material that had been orbiting near it. These objects do not collide with one another because they are too far apart, sometimes in orbital resonance.[68]


Main article: Exoplanet § Definition

The 2006 IAU definition presents some challenges for exoplanets because the language is specific to the Solar System and the criteria of roundness and orbital zone clearance are not presently observable for exoplanets.[64] The IAU working group on extrasolar planets (WGESP) issued a working definition in 2001 and amended it in 2003.[69] In 2018, this definition was reassessed and updated as knowledge of exoplanets increased.[69] The current official working definition of an exoplanet is as follows:[70]

  1. Objects with true masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars, brown dwarfs or stellar remnants and that have a mass ratio with the central object below the L4/L5 instability (M/Mcentral < 2/(25+621) are "planets" (no matter how they formed). The minimum mass/size required for an extrasolar object to be considered a planet should be the same as that used in our Solar System.
  2. Substellar objects with true masses above the limiting mass for thermonuclear fusion of deuterium are "brown dwarfs", no matter how they formed nor where they are located.
  3. Free-floating objects in young star clusters with masses below the limiting mass for thermonuclear fusion of deuterium are not "planets", but are "sub-brown dwarfs" (or whatever name is most appropriate).[70]

The IAU noted that this definition could be expected to evolve as knowledge improves.[70] A 2022 review article discussing the history and rationale of this definition suggested that the words "in young star clusters" should be deleted in clause 3, as such objects have now been found elsewhere, and that the term "sub-brown dwarfs" should be replaced by the more current "free-floating planetary mass objects".[69]

Planetary-mass object

Main article: Planetary-mass object

See also: List of gravitationally rounded objects of the Solar System

The planetary-mass moons to scale, compared with Mercury, Venus, Earth, Mars, and Pluto. Borderline Proteus and Nereid (about the same size as round Mimas) have been included. Unimaged Dysnomia (intermediate in size between Tethys and Enceladus) is not shown; it is in any case probably not a solid body.[71]

Geoscientists often reject the IAU definition, preferring to consider round moons and dwarf planets as also being planets. Some scientists who accept the IAU definition of "planet" use other terms for bodies satisfying geophysical planet definitions, such as "world".[7] The term "planetary mass object" has also been used to refer to ambiguous situations concerning exoplanets, such as objects with mass typical for a planet that are free-floating or orbit a brown dwarf instead of a star.[69]

Mythology and naming

See also: Weekday names and classical planet

Naming of planets differs between planets of the Solar System and Exoplanets (planets of other planetary systems). Latter are commonly named after their parent star and their order of discovery within its planetary system, such as Proxima Centauri b.

The names for the planets of the Solar System (other than Earth) in the English language are derived from naming practices developed consecutively by the Babylonians, Greeks and Romans of antiquity. The practice of grafting the names of gods onto the planets was almost certainly borrowed from the Babylonians by the ancient Greeks, and thereafter from the Greeks by the Romans. The Babylonians named Venus after the Sumerian goddess of love with the Akkadian name Ishtar; Mars after their god of war, Nergal; Mercury after their god of wisdom Nabu; and Jupiter after their chief god, Marduk.[72] There are too many concordances between Greek and Babylonian naming conventions for them to have arisen separately.[17] Given the differences in mythology, the correspondence was not perfect. For instance, the Babylonian Nergal was a god of war, and thus the Greeks identified him with Ares. Unlike Ares, Nergal was also a god of pestilence and ruler of the underworld.[73][74][75]

In ancient Greece, the two great luminaries, the Sun and the Moon, were called Helios and Selene, two ancient Titanic deities; the slowest planet, Saturn, was called Phainon, the shiner; followed by Phaethon, Jupiter, "bright"; the red planet, Mars was known as Pyroeis, the "fiery"; the brightest, Venus, was known as Phosphoros, the light bringer; and the fleeting final planet, Mercury, was called Stilbon, the gleamer. The Greeks assigned each planet to one among their pantheon of gods, the Olympians and the earlier Titans:[17]

The Greek gods of Olympus, after whom the Solar System's Roman names of the planets are derived

Although modern Greeks still use their ancient names for the planets, other European languages, because of the influence of the Roman Empire and, later, the Catholic Church, use the Roman (Latin) names rather than the Greek ones. The Romans inherited Proto-Indo-European mythology as the Greeks did and shared with them a common pantheon under different names, but the Romans lacked the rich narrative traditions that Greek poetic culture had given their gods. During the later period of the Roman Republic, Roman writers borrowed much of the Greek narratives and applied them to their own pantheon, to the point where they became virtually indistinguishable.[76] When the Romans studied Greek astronomy, they gave the planets their own gods' names: Mercurius (for Hermes), Venus (Aphrodite), Mars (Ares), Iuppiter (Zeus) and Saturnus (Cronus). Some Romans, following a belief possibly originating in Mesopotamia but developed in Hellenistic Egypt, believed that the seven gods after whom the planets were named took hourly shifts in looking after affairs on Earth. The order of shifts went Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon (from the farthest to the closest planet).[77] Therefore, the first day was started by Saturn (1st hour), second day by Sun (25th hour), followed by Moon (49th hour), Mars, Mercury, Jupiter and Venus. Because each day was named by the god that started it, this became the order of the days of the week in the Roman calendar.[78] In English, Saturday, Sunday, and Monday are straightforward translations of these Roman names. The other days were renamed after Tīw (Tuesday), Wōden (Wednesday), Þunor (Thursday), and Frīġ (Friday), the Anglo-Saxon gods considered similar or equivalent to Mars, Mercury, Jupiter, and Venus, respectively.[79]

Earth's name in English is not derived from Greco-Roman mythology. Because it was only generally accepted as a planet in the 17th century,[34] there is no tradition of naming it after a god. (The same is true, in English at least, of the Sun and the Moon, though they are no longer generally considered planets.) The name originates from the Old English word eorþe, which was the word for "ground" and "dirt" as well as the world itself.[80] As with its equivalents in the other Germanic languages, it derives ultimately from the Proto-Germanic word erþō, as can be seen in the English earth, the German Erde, the Dutch aarde, and the Scandinavian jord. Many of the Romance languages retain the old Roman word terra (or some variation of it) that was used with the meaning of "dry land" as opposed to "sea".[81] The non-Romance languages use their own native words. The Greeks retain their original name, Γή (Ge).[82]

Non-European cultures use other planetary-naming systems. India uses a system based on the Navagraha, which incorporates the seven traditional planets and the ascending and descending lunar nodes Rahu and Ketu. The planets are Surya 'Sun', Chandra 'Moon', Budha for Mercury, Shukra ('bright') for Venus, Mangala (the god of war) for Mars, Bṛhaspati (councilor of the gods) for Jupiter, and Shani (symbolic of time) for Saturn.[83]

The native Persian names of most of the planets are based on identifications of the Mesopotamian gods with Iranian gods, analogous to the Greek and Latin names. Mercury is Tir (تیر) for the western Iranian god Tīriya (patron of scribes), analogous to Nabu; Venus is Nāhid (ناهید) for Anahita; Mars is Bahrām (بهرام) for Verethragna; and Jupiter is Hormoz (هرمز) for Ahura Mazda. The Persian name for Saturn, Keyvān (کیوان), is a borrowing from Akkadian kajamānu, meaning "the permanent, steady".[84]

China and the countries of eastern Asia historically subject to Chinese cultural influence (such as Japan, Korea and Vietnam) use a naming system based on the five Chinese elements: water (Mercury 星 "water star"), metal (Venus 星 "metal star"), fire (Mars 星 "fire star"), wood (Jupiter 星 "wood star") and earth (Saturn 星 "earth star").[78] The names of Uranus (王星 "sky king star"), Neptune (王星 "sea king star"), and Pluto (王星 "underworld king star") in Chinese, Korean, and Japanese are calques based on the roles of those gods in Roman and Greek mythology.[85][86][b] In the 19th century, Alexander Wylie and Li Shanlan calqued the names of the first 117 asteroids into Chinese, and many of their names are still used today, e.g. Ceres (神星 "grain goddess star"), Pallas (神星 "wisdom goddess star"), Juno (神星 "marriage goddess star"), Vesta (神星 "hearth goddess star"), and Hygiea (神星 "health goddess star").[88] Such translations were extended to some later minor planets, including some of the dwarf planets discovered in the 21st century, e.g. Haumea (神星 "pregnancy goddess star", Makemake (神星 "bird goddess star"), and Eris (神星 "quarrel goddess star"). However, except for the better-known asteroids and dwarf planets, many of them are rare outside Chinese astronomical dictionaries.[85]

In traditional Hebrew astronomy, the seven traditional planets have (for the most part) descriptive names – the Sun is חמה Ḥammah or "the hot one", the Moon is לבנה Levanah or "the white one", Venus is כוכב נוגה Kokhav Nogah or "the bright planet", Mercury is כוכב Kokhav or "the planet" (given its lack of distinguishing features), Mars is מאדים Ma'adim or "the red one", and Saturn is שבתאי Shabbatai or "the resting one" (in reference to its slow movement compared to the other visible planets).[89] The odd one out is Jupiter, called צדק Tzedeq or "justice".[89] Hebrew names were chosen for Uranus (אורון Oron, "small light") and Neptune (רהב Rahab, a Biblical sea monster) in 2009;[90] prior to that the names "Uranus" and "Neptune" had simply been borrowed.[91] The etymologies for the Arabic names of the planets are less well understood. Mostly agreed among scholars are Venus الزهرة (az-Zuhara, "the bright one"[92]), Earth الأرض (al-ʾArḍ, from the same root as eretz), and Saturn زُحَل (Zuḥal, "withdrawer"[93]). Multiple suggested etymologies exist for Mercury عُطَارِد (ʿUṭārid), Mars اَلْمِرِّيخ (al-Mirrīkh), and Jupiter المشتري (al-Muštarī), but there is no agreement among scholars.[94][95][96][97]

When subsequent planets were discovered in the 18th and 19th centuries, Uranus was named for a Greek deity and Neptune for a Roman one (the counterpart of Poseidon). The asteroids were initially named from mythology as well – Ceres, Juno, and Vesta are major Roman goddesses, and Pallas is an epithet of the major Greek goddess Athena – but as more and more were discovered, they first started being named after more minor goddesses, and the mythological restriction was dropped starting from the twentieth asteroid Massalia in 1852.[98] Pluto was given a classical name, as it was considered a major planet when it was discovered. After more objects were discovered beyond Neptune, naming conventions depending on their orbits were put in place: those in the 2:3 resonance with Neptune (the plutinos) are given names from underworld myths, while others are given names from creation myths. Most of the trans-Neptunian dwarf planets are named after gods and goddesses from other cultures (e.g. Quaoar is named after a Tongva god), except for Orcus and Eris which continued the Roman and Greek scheme.[99][100]

The moons (including the planetary-mass ones) are generally given names with some association with their parent planet. The planetary-mass moons of Jupiter are named after four of Zeus' lovers (or other sexual partners); those of Saturn are named after Cronus' brothers and sisters, the Titans; those of Uranus are named after characters from Shakespeare and Pope (originally specifically from fairy mythology,[101] but that ended with the naming of Miranda). Neptune's planetary-mass moon Triton is named after the god's son; Pluto's planetary-mass moon Charon is named after the ferryman of the dead, who carries the souls of the newly deceased to the underworld (Pluto's domain).[102]


Main article: Planetary symbol

Most common planetary symbols
⛢ or ♅

The written symbols for Mercury, Venus, Jupiter, Saturn and possibly Mars have been traced to forms found in late Greek papyrus texts.[103] The symbols for Jupiter and Saturn are identified as monograms of the corresponding Greek names, and the symbol for Mercury is a stylized caduceus.[103]

According to Annie Scott Dill Maunder, antecedents of the planetary symbols were used in art to represent the gods associated with the classical planets. Bianchini's planisphere, discovered by Francesco Bianchini in the 18th century but produced in the 2nd century,[104] shows Greek personifications of planetary gods charged with early versions of the planetary symbols. Mercury has a caduceus; Venus has, attached to her necklace, a cord connected to another necklace; Mars, a spear; Jupiter, a staff; Saturn, a scythe; the Sun, a circlet with rays radiating from it; and the Moon, a headdress with a crescent attached.[105] The modern shapes with the cross-marks first appeared around the 16th century. According to Maunder, the addition of crosses appears to be "an attempt to give a savour of Christianity to the symbols of the old pagan gods."[105] Earth itself was not considered a classical planet; its symbol descends from a pre-heliocentric symbol for the four corners of the world.[106]

When further planets were discovered orbiting the Sun, symbols were invented for them. The most common astronomical symbol for Uranus, ⛢,[107] was invented by Johann Gottfried Köhler, and was intended to represent the newly discovered metal platinum.[108][109] An alternative symbol, ♅, was invented by Jérôme Lalande, and represents a globe with a H on top, for Uranus' discoverer Herschel.[110] Today, ⛢ is mostly used by astronomers and ♅ by astrologers, though it is possible to find each symbol in the other context.[107] The first few asteroids were similarly given abstract symbols, e.g. Ceres' sickle (⚳), Pallas' spear (⚴), Juno's sceptre (⚵), and Vesta's hearth (⚶), but as their number rose further and further, this practice stopped in favour of numbering them instead (Massalia, the first asteroid not named from mythology, is also the first asteroid that was not assigned a symbol by its discoverer).[6] Neptune's symbol (♆) represents the god's trident.[109] The astronomical symbol for Pluto is a P-L monogram (♇),[111] though it has become less common since the IAU definition reclassified Pluto.[112] Since Pluto's reclassification, NASA has used the traditional astrological symbol of Pluto (⯓), a planetary orb over Pluto's bident.[112]

Some rarer planetary symbols in Unicode
♇ or ⯓

The IAU discourages the use of planetary symbols in modern journal articles in favour of one-letter or (to disambiguate Mercury and Mars) two-letter abbreviations for the major planets. The symbols for the Sun and Earth are nonetheless common, as solar mass, Earth mass and similar units are common in astronomy.[113] Other planetary symbols today are mostly encountered in astrology. Astrologers have resurrected the old astronomical symbols for the first few asteroids, and continue to invent symbols for other objects.[112] Unicode includes some relatively standard astrological symbols for minor planets, including dwarf planets discovered in the 21st century, though astronomical use of any of them is rare. In particular, the Eris symbol is a traditional one from Discordianism, a religion worshipping the goddess Eris. The other dwarf-planet symbols are mostly initialisms (except Haumea) in the native scripts of the cultures they come from; they also represent something associated with the corresponding deity or culture, e.g. Orcus' gape, Makemake's face, or Gonggong's snake-tail.[112][114]


Main article: Nebular hypothesis

Artists' impressions
A protoplanetary disk
Asteroids colliding during planet formation

It is not known with certainty how planets are built. The prevailing theory is that they are formed during the collapse of a nebula into a thin disk of gas and dust. A protostar forms at the core, surrounded by a rotating protoplanetary disk. Through accretion (a process of sticky collision) dust particles in the disk steadily accumulate mass to form ever-larger bodies. Local concentrations of mass known as planetesimals form, and these accelerate the accretion process by drawing in additional material by their gravitational attraction. These concentrations become ever denser until they collapse inward under gravity to form protoplanets.[115] After a planet reaches a mass somewhat larger than Mars' mass, it begins to accumulate an extended atmosphere,[116] greatly increasing the capture rate of the planetesimals by means of atmospheric drag.[117][118] Depending on the accretion history of solids and gas, a giant planet, an ice giant, or a terrestrial planet may result.[119][120][121] It is thought that the regular satellites of Jupiter, Saturn, and Uranus formed in a similar way;[122][123] however, Triton was likely captured by Neptune,[124] and Earth's Moon[125] and Pluto's Charon might have formed in collisions.[126]

When the protostar has grown such that it ignites to form a star, the surviving disk is removed from the inside outward by photoevaporation, the solar wind, Poynting–Robertson drag and other effects.[127][128] Thereafter there still may be many protoplanets orbiting the star or each other, but over time many will collide, either to form a larger, combined protoplanet or release material for other protoplanets to absorb.[129] Those objects that have become massive enough will capture most matter in their orbital neighbourhoods to become planets. Protoplanets that have avoided collisions may become natural satellites of planets through a process of gravitational capture, or remain in belts of other objects to become either dwarf planets or small bodies.[130][131]

Supernova remnant ejecta producing planet-forming material

The energetic impacts of the smaller planetesimals (as well as radioactive decay) will heat up the growing planet, causing it to at least partially melt. The interior of the planet begins to differentiate by density, with higher density materials sinking toward the core.[132] Smaller terrestrial planets lose most of their atmospheres because of this accretion, but the lost gases can be replaced by outgassing from the mantle and from the subsequent impact of comets.[133] (Smaller planets will lose any atmosphere they gain through various escape mechanisms.[134])

With the discovery and observation of planetary systems around stars other than the Sun, it is becoming possible to elaborate, revise or even replace this account. The level of metallicity—an astronomical term describing the abundance of chemical elements with an atomic number greater than 2 (helium)—appears to determine the likelihood that a star will have planets.[135][136] Hence, a metal-rich population I star is more likely to have a substantial planetary system than a metal-poor, population II star.[137]

Solar System

Main article: Solar System

The Solar System, including the Sun, planets, dwarf planets, and the larger moons (except Iapetus). Distances between the bodies are not to scale.

According to the IAU definition, there are eight planets in the Solar System, which are (in increasing distance from the Sun):[1] Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Jupiter is the largest, at 318 Earth masses, whereas Mercury is the smallest, at 0.055 Earth masses.[138]

The planets of the Solar System can be divided into categories based on their composition. Terrestrials are similar to Earth, with bodies largely composed of rock and metal: Mercury, Venus, Earth, and Mars. Earth is the largest terrestrial planet.[139] Giant planets are significantly more massive than the terrestrials: Jupiter, Saturn, Uranus, and Neptune.[139] They differ from the terrestrial planets in composition. The gas giants, Jupiter and Saturn, are primarily composed of hydrogen and helium and are the most massive planets in the Solar System. Saturn is one third as massive as Jupiter, at 95 Earth masses.[140] The ice giants, Uranus and Neptune, are primarily composed of low-boiling-point materials such as water, methane, and ammonia, with thick atmospheres of hydrogen and helium. They have a significantly lower mass than the gas giants (only 14 and 17 Earth masses).[140]

Dwarf planets are gravitationally rounded, but have not cleared their orbits of other bodies. In increasing order of average distance from the Sun, the ones generally agreed among astronomers are Ceres, Orcus, Pluto, Haumea, Quaoar, Makemake, Gonggong, Eris and Sedna.[57] Ceres is the largest object in the asteroid belt, located between the orbits of Mars and Jupiter. The other eight all orbit beyond Neptune. Orcus, Pluto, Haumea, Quaoar, and Makemake orbit in the Kuiper belt, which is a second belt of small Solar System bodies beyond the orbit of Neptune. Gonggong and Eris orbit in the scattered disc, which is somewhat further out and, unlike the Kuiper belt, is unstable towards interactions with Neptune. Sedna is the largest known detached object, a population that never comes close enough to the Sun to interact with any of the classical planets; the origins of their orbits are still being debated. All nine are similar to terrestrial planets in having a solid surface, but they are made of ice and rock, rather than rock and metal. Moreover, all of them are smaller than Mercury, with Pluto being the largest known dwarf planet, and Eris being the most massive known.[141][142]

There are at least nineteen planetary-mass moons or satellite planets—moons large enough to take on ellipsoidal shapes:[3]

The Moon, Io, and Europa have compositions similar to the terrestrial planets; the others are made of ice and rock like the dwarf planets, with Tethys being made of almost pure ice. (Europa is often considered an icy planet, though, because its surface ice layer makes it difficult to study its interior.[3][143]) Ganymede and Titan are larger than Mercury by radius, and Callisto almost equals it, but all three are much less massive. Mimas is the smallest object generally agreed to be a geophysical planet, at about six millionths of Earth's mass, though there are many larger bodies that may not be geophysical planets (e.g. Salacia).[57]

Planetary attributes

The tables below summarise some properties of objects generally agreed to satisfy geophysical planet definitions. There are many smaller dwarf planet candidates, such as Salacia, that have not been included in the tables because astronomers disagree on whether or not they are dwarf planets. Likewise, objects such as Pallas and Vesta that developed planetary geology but are no longer round are also excluded, though some authors would include them regardless. The diameters, masses, orbital periods, and rotation periods of the major planets are available from the Jet Propulsion Laboratory.[138] JPL also provides their semi-major axes, inclinations, and eccentricities of planetary orbits,[144] and the axial tilts are taken from their Horizons database.[145] Other information is summarized by NASA.[146] The data for the dwarf planets and planetary-mass moons is taken from list of gravitationally rounded objects of the Solar System, with sources listed there.

Name Equatorial
Mass Semi-major axis (AU) Orbital period
(Julian years)
to the ecliptic
Rotation period
Axial tilt (°) Rings Atmosphere
Major planets
☿ Mercury 0.383 0.06 0.39 0.24 7.00 0.206 58.65 0 0.04 no minimal
♀ Venus 0.949 0.81 0.72 0.62 3.39 0.007 243.02 0 177.30 no CO2, N2
🜨 Earth 1.000 1.00 1.00 1.00 0.0 0.017 1.00 1 23.44 no N2, O2, Ar
♂ Mars 0.532 0.11 1.52 1.88 1.85 0.093 1.03 2 25.19 no CO2, N2, Ar
♃ Jupiter 11.209 317.83 5.20 11.86 1.30 0.048 0.41 95 3.13 yes H2, He
♄ Saturn 9.449 95.16 9.54 29.45 2.49 0.054 0.44 146 26.73 yes H2, He
⛢ Uranus 4.007 14.54 19.19 84.02 0.773 0.047 0.72 27 97.77 yes H2, He, CH4
♆ Neptune 3.883 17.15 30.07 164.79 1.77 0.009 0.67 14 28.32 yes H2, He, CH4
Dwarf planets
⚳ Ceres 0.0742 0.00016 2.77 4.60 10.59 0.080 0.38 0 4 no minimal
🝿 Orcus 0.072 0.0001 39.42 247.5 20.59 0.226 9.54? 1 ? ? ?
♇ Pluto 0.186 0.0022 39.48 247.9 17.14 0.249 6.39 5 119.6 no N2, CH4, CO
🝻 Haumea 0.13 0.0007 43.34 283.8 28.21 0.195 0.16 2 126? yes ?
🝾 Quaoar 0.085 0.0002 43.69 288.0 7.99 0.038 0.74 1 14? yes ?
🝼 Makemake 0.11 0.0005 45.79 306.2 28.98 0.161 0.95 1 ? ? minimal
🝽 Gonggong 0.10 0.0003 67.33 552.5 30.74 0.506 0.93 1 ? ? ?
⯰ Eris 0.18 0.0028 67.67 559 44.04 0.436 15.79 1 78? ? ?
⯲ Sedna 0.078 ? 525.86 12059 11.93 0.855 0.43 0 ? ? ?
Color legend:   terrestrial planets   gas giants   ice giants (both categories of giant planets  dwarf planets

Measured relative to Earth.
The Earth's mass is approximately 5.972 × 1024 kilograms, and its equatorial radius is approximately 6,378 kilometres.[138]

As all the planetary-mass moons exhibit synchronous rotation, their rotation periods equal their orbital periods.

Planetary-mass moons
Name Equatorial
Mass Semi-major axis (km) Orbital period
to primary's equator
Axial tilt (°) Atmosphere
☾ Moon 0.272 0.0123 384,399 27.322 18.29–28.58 0.0549 6.68 minimal
♃1 Io 0.285 0.0150 421,600 1.769 0.04 0.0041 ≈0 minimal
♃2 Europa 0.246 0.00804 670,900 3.551 0.47 0.009 ≈0.1 minimal
♃3 Ganymede 0.413 0.0248 1,070,400 7.155 1.85 0.0013 ≈0.2 minimal
♃4 Callisto 0.378 0.0180 1,882,700 16.689 0.2 0.0074 ≈0–2 minimal
♄1 Mimas 0.031 0.00000628 185,520 0.942 1.51 0.0202 ≈0
♄2 Enceladus 0.04 0.0000181 237,948 1.370 0.02 0.0047 ≈0 minimal
♄3 Tethys 0.084 0.000103 294,619 1.888 1.51 0.02 ≈0
♄4 Dione 0.088 0.000183 377,396 2.737 0.019 0.002 ≈0 minimal
♄5 Rhea 0.12 0.000386 527,108 4.518 0.345 0.001 ≈0 minimal
♄6 Titan 0.404 0.0225 1,221,870 15.945 0.33 0.0288 ≈0.3 N2, CH4
♄8 Iapetus 0.115 0.000302 3,560,820 79.322 14.72 0.0286 ≈0
⛢5 Miranda 0.037 0.0000110 129,390 1.414 4.22 0.0013 ≈0
⛢1 Ariel 0.091 0.000226 190,900 2.520 0.31 0.0012 ≈0
⛢2 Umbriel 0.092 0.00020 266,000 4.144 0.36 0.005 ≈0
⛢3 Titania 0.124 0.00059 436,300 8.706 0.14 0.0011 ≈0
⛢4 Oberon 0.119 0.000505 583,519 13.46 0.10 0.0014 ≈0
♆1 Triton 0.212 0.00358 354,759 5.877 157 0.00002 ≈0.7 N2, CH4
♇1 Charon 0.095 0.000255 17,536 6.387 0.001 0.0022 ≈0
Color legend:   predominantly rocky   predominantly icy

Measured relative to Earth.


Main article: Exoplanet

Exoplanet detections per year as of June 2022 (by NASA Exoplanet Archive)[147]

An exoplanet (extrasolar planet) is a planet outside the Solar System. As of 1 August 2023, there are 5,484 confirmed exoplanets in 4,047 planetary systems, with 875 systems having more than one planet.[148] Known exoplanets range in size from gas giants about twice as large as Jupiter down to just over the size of the Moon. Analysis of gravitational microlensing data suggests a minimum average of 1.6 bound planets for every star in the Milky Way.[149]

In early 1992, radio astronomers Aleksander Wolszczan and Dale Frail announced the discovery of two planets orbiting the pulsar PSR 1257+12.[46] This discovery was confirmed, and is generally considered to be the first definitive detection of exoplanets. Researchers suspect they formed from a disk remnant left over from the supernova that produced the pulsar.[150]

The first confirmed discovery of an extrasolar planet orbiting an ordinary main-sequence star occurred on 6 October 1995, when Michel Mayor and Didier Queloz of the University of Geneva announced the detection of 51 Pegasi b, an exoplanet around 51 Pegasi.[151] From then until the Kepler mission most known extrasolar planets were gas giants comparable in mass to Jupiter or larger as they were more easily detected. The catalog of Kepler candidate planets consists mostly of planets the size of Neptune and smaller, down to smaller than Mercury.[152][153]

In 2011, the Kepler Space Telescope team reported the discovery of the first Earth-sized extrasolar planets orbiting a Sun-like star, Kepler-20e and Kepler-20f.[154][155][156] Since that time, more than 100 planets have been identified that are approximately the same size as Earth, 20 of which orbit in the habitable zone of their star – the range of orbits where a terrestrial planet could sustain liquid water on its surface, given enough atmospheric pressure.[157][158][159] One in five Sun-like stars is thought to have an Earth-sized planet in its habitable zone, which suggests that the nearest would be expected to be within 12 light-years distance from Earth.[c] The frequency of occurrence of such terrestrial planets is one of the variables in the Drake equation, which estimates the number of intelligent, communicating civilizations that exist in the Milky Way.[162]

There are types of planets that do not exist in the Solar System: super-Earths and mini-Neptunes, which have masses between that of Earth and Neptune. Such planets could be rocky like Earth or a mixture of volatiles and gas like Neptune—the dividing line between the two possibilities is currently thought to occur at about twice the mass of Earth.[163] The planet Gliese 581c, with mass 5.5–10.4 times the mass of Earth,[164] attracted attention upon its discovery for potentially being in the habitable zone,[165] though later studies concluded that it is actually too close to its star to be habitable.[166] Exoplanets have been found that are much closer to their parent star than any planet in the Solar System is to the Sun. Mercury, the closest planet to the Sun at 0.4 AU, takes 88 days for an orbit, but ultra-short period planets can orbit in less than a day. The Kepler-11 system has five of its planets in shorter orbits than Mercury's, all of them much more massive than Mercury. There are hot Jupiters, such as 51 Pegasi b,[151] that orbit very close to their star and may evaporate to become chthonian planets, which are the leftover cores. There are also exoplanets that are much farther from their star. Neptune is 30 AU from the Sun and takes 165 years to orbit, but there are exoplanets that are thousands of AU from their star and take more than a million years to orbit. e.g. COCONUTS-2b.[167]


Although each planet has unique physical characteristics, a number of broad commonalities do exist among them. Some of these characteristics, such as rings or natural satellites, have only as yet been observed in planets in the Solar System, whereas others are commonly observed in extrasolar planets.[168]

Dynamic characteristics


Main articles: Orbit and orbital elements

See also: Kepler's laws of planetary motion and Exoplanetology § Orbital parameters

The orbit of the planet Neptune compared to that of Pluto. Note the elongation of Pluto's orbit in relation to Neptune's (eccentricity), as well as its large angle to the ecliptic (inclination).

In the Solar System, all the planets orbit the Sun in the same direction as the Sun rotates: counter-clockwise as seen from above the Sun's north pole. At least one extrasolar planet, WASP-17b, has been found to orbit in the opposite direction to its star's rotation.[169] The period of one revolution of a planet's orbit is known as its sidereal period or year.[170] A planet's year depends on its distance from its star; the farther a planet is from its star, the longer the distance it must travel and the slower its speed, since it is less affected by its star's gravity.

No planet's orbit is perfectly circular, and hence the distance of each from the host star varies over the course of its year. The closest approach to its star is called its periastron, or perihelion in the Solar System, whereas its farthest separation from the star is called its apastron (aphelion). As a planet approaches periastron, its speed increases as it trades gravitational potential energy for kinetic energy, just as a falling object on Earth accelerates as it falls. As the planet nears apastron, its speed decreases, just as an object thrown upwards on Earth slows down as it reaches the apex of its trajectory.[171]

Each planet's orbit is delineated by a set of elements:

Axial tilt

Main article: Axial tilt

Earth's axial tilt is about 23.4°. It oscillates between 22.1° and 24.5° on a 41,000-year cycle and is currently decreasing.

Planets have varying degrees of axial tilt; they spin at an angle to the plane of their stars' equators. This causes the amount of light received by each hemisphere to vary over the course of its year; when the northern hemisphere points away from its star, the southern hemisphere points towards it, and vice versa. Each planet therefore has seasons, resulting in changes to the climate over the course of its year. The time at which each hemisphere points farthest or nearest from its star is known as its solstice. Each planet has two in the course of its orbit; when one hemisphere has its summer solstice with its day being the longest, the other has its winter solstice when its day is shortest. The varying amount of light and heat received by each hemisphere creates annual changes in weather patterns for each half of the planet. Jupiter's axial tilt is very small, so its seasonal variation is minimal; Uranus, on the other hand, has an axial tilt so extreme it is virtually on its side, which means that its hemispheres are either continually in sunlight or continually in darkness around the time of its solstices.[177] In the Solar System, Mercury, Venus, Ceres, and Jupiter have very small tilts; Pallas, Uranus, and Pluto have extreme ones; and Earth, Mars, Vesta, Saturn, and Neptune have moderate ones.[178][179][180][181] Among extrasolar planets, axial tilts are not known for certain, though most hot Jupiters are believed to have a negligible axial tilt as a result of their proximity to their stars.[182] Similarly, the axial tilts of the planetary-mass moons are near zero,[183] with Earth's Moon at 6.687° as the biggest exception;[184] additionally, Callisto's axial tilt varies between 0 and about 2 degrees on timescales of thousands of years.[185]


See also: Exoplanetology § Rotation and axial tilt

The planets rotate around invisible axes through their centres. A planet's rotation period is known as a stellar day. Most of the planets in the Solar System rotate in the same direction as they orbit the Sun, which is counter-clockwise as seen from above the Sun's north pole. The exceptions are Venus[186] and Uranus,[187] which rotate clockwise, though Uranus's extreme axial tilt means there are differing conventions on which of its poles is "north", and therefore whether it is rotating clockwise or anti-clockwise.[188] Regardless of which convention is used, Uranus has a retrograde rotation relative to its orbit.[187]

Comparison of the rotation period (sped up 10 000 times, negative values denoting retrograde), flattening and axial tilt of the planets and the Moon (SVG animation)

The rotation of a planet can be induced by several factors during formation. A net angular momentum can be induced by the individual angular momentum contributions of accreted objects. The accretion of gas by the giant planets contributes to the angular momentum. Finally, during the last stages of planet building, a stochastic process of protoplanetary accretion can randomly alter the spin axis of the planet.[189] There is great variation in the length of day between the planets, with Venus taking 243 days to rotate, and the giant planets only a few hours.[146] The rotational periods of extrasolar planets are not known, but for hot Jupiters, their proximity to their stars means that they are tidally locked (that is, their orbits are in sync with their rotations). This means, they always show one face to their stars, with one side in perpetual day, the other in perpetual night.[190] Mercury and Venus, the closest planets to the Sun, similarly exhibit very slow rotation: Mercury is tidally locked into a 3:2 spin–orbit resonance (rotating three times for every two revolutions around the Sun),[191] and Venus' rotation may be in equilibrium between tidal forces slowing it down and atmospheric tides created by solar heating speeding it up.[192][193]

All the large moons are tidally locked to their parent planets;[194] Pluto and Charon are tidally locked to each other,[195] as are Eris and Dysnomia.[196] Orcus and its moon Vanth may be another example of mutual tidal locking, but the data is not conclusive.[197] The other dwarf planets with known rotation periods rotate faster than Earth; Haumea rotates so fast that it has been distorted into a triaxial ellipsoid.[198] The exoplanet Tau Boötis b and its parent star Tau Boötis appear to be mutually tidally locked.[199][200]

Orbital clearing

Main article: Clearing the neighbourhood

The defining dynamic characteristic of a planet, according to the IAU definition, is that it has cleared its neighborhood. A planet that has cleared its neighborhood has accumulated enough mass to gather up or sweep away all the planetesimals in its orbit. In effect, it orbits its star in isolation, as opposed to sharing its orbit with a multitude of similar-sized objects. As described above, this characteristic was mandated as part of the IAU's official definition of a planet in August 2006.[1] Although to date this criterion only applies to the Solar System, a number of young extrasolar systems have been found in which evidence suggests orbital clearing is taking place within their circumstellar discs.[201]

Physical characteristics

Size and shape

See also: Earth § Size and shape, Astronomical body § Size, and Planetary coordinate system

Gravity causes planets to be pulled into a roughly spherical shape, so a planet's size can be expressed roughly by an average radius (for example, Earth radius or Jupiter radius). However, planets are not perfectly spherical; for example, the Earth's rotation causes it to be slightly flattened at the poles with a bulge around the equator.[202] Therefore, a better approximation of Earth's shape is an oblate spheroid, whose equatorial diameter is 43 kilometers (27 mi) larger than the pole-to-pole diameter.[203] Generally, a planet's shape may be described by giving polar and equatorial radii of a spheroid or specifying a reference ellipsoid. From such a specification, the planet's flattening, surface area, and volume can be calculated; its normal gravity can be computed knowing its size, shape, rotation rate and mass.[204]


Main article: Planetary mass

A planet's defining physical characteristic is that it is massive enough for the force of its own gravity to dominate over the electromagnetic forces binding its physical structure, leading to a state of hydrostatic equilibrium. This effectively means that all planets are spherical or spheroidal. Up to a certain mass, an object can be irregular in shape, but beyond that point, which varies depending on the chemical makeup of the object, gravity begins to pull an object towards its own centre of mass until the object collapses into a sphere.[205]

Mass is the prime attribute by which planets are distinguished from stars. While the lower stellar mass limit is estimated to be around 75 times that of Jupiter (MJ), the upper planetary mass limit for planethood is only roughly 13 MJ for objects with solar-type isotopic abundance, beyond which it achieves conditions suitable for nuclear fusion of deuterium. Other than the Sun, no objects of such mass exist in the Solar System; but there are exoplanets of this size. The 13 MJ limit is not universally agreed upon and the Extrasolar Planets Encyclopaedia includes objects up to 60 MJ,[206] and the Exoplanet Data Explorer up to 24 MJ.[207] The mass-radius relationship does not change appreciably with the onset of deuterium fusion, with radius remaining roughly constant as mass increases from one Saturn mass (beginning of significant self-compression) to about 0.08 M (around 80 MJ, the onset of hydrogen burning and becoming a red dwarf), and thus some authors argue that brown dwarfs should be considered as high-mass Jovian planets.[163]

The smallest known exoplanet with an accurately known mass is PSR B1257+12A, one of the first extrasolar planets discovered, which was found in 1992 in orbit around a pulsar. Its mass is roughly half that of the planet Mercury.[208] Even smaller is WD 1145+017 b, orbiting a white dwarf; its mass is roughly that of the dwarf planet Haumea, and it is typically termed a minor planet.[209] The smallest known planet orbiting a main-sequence star other than the Sun is Kepler-37b, with a mass (and radius) that is probably slightly higher than that of the Moon.[153] The smallest object in the Solar System generally agreed to be a geophysical planet is Saturn's moon Mimas, with a radius about 3.1% of Earth's and a mass about 0.00063% of Earth's.[210] Saturn's smaller moon Phoebe, currently an irregular body of 1.7% Earth's radius[211] and 0.00014% Earth's mass,[210] is thought to have attained hydrostatic equilibrium and differentiation early in its history before being battered out of shape by impacts.[212] Some asteroids may be fragments of protoplanets that began to accrete and differentiate, but suffered catastrophic collisions, leaving only a metallic or rocky core today,[213][214][215] or a reaccumulation of the resulting debris.[63]

Internal differentiation

Main article: Planetary differentiation

Illustration of the interior of Jupiter, with a rocky core overlaid by a deep layer of metallic hydrogen

Every planet began its existence in an entirely fluid state; in early formation, the denser, heavier materials sank to the centre, leaving the lighter materials near the surface. Each therefore has a differentiated interior consisting of a dense planetary core surrounded by a mantle that either is or was a fluid. The terrestrial planets' mantles are sealed within hard crusts,[216] but in the giant planets the mantle simply blends into the upper cloud layers. The terrestrial planets have cores of elements such as iron and nickel, and mantles of silicates. Jupiter and Saturn are believed to have cores of rock and metal surrounded by mantles of metallic hydrogen.[217] Uranus and Neptune, which are smaller, have rocky cores surrounded by mantles of water, ammonia, methane and other ices.[218] The fluid action within these planets' cores creates a geodynamo that generates a magnetic field.[216] Similar differentiation processes are believed to have occurred on some of the large moons and dwarf planets,[57] though the process may not always have been completed: Ceres, Callisto, and Titan appear to be incompletely differentiated.[219][220] The asteroid Vesta, though not a dwarf planet because it was battered by impacts out of roundness, has a differentiated interior[221] similar to that of Venus, Earth, and Mars.[215]


Main articles: Atmosphere and extraterrestrial atmospheres

See also: Extraterrestrial skies

Earth's atmosphere

All of the Solar System planets except Mercury[222] have substantial atmospheres because their gravity is strong enough to keep gases close to the surface. Saturn's largest moon Titan also has a substantial atmosphere thicker than that of Earth;[223] Neptune's largest moon Triton[224] and the dwarf planet Pluto have more tenuous atmospheres.[225] The larger giant planets are massive enough to keep large amounts of the light gases hydrogen and helium, whereas the smaller planets lose these gases into space.[226] Analysis of exoplanets suggests that the threshold for being able to hold on to these light gases occurs at about 2.0+0.7
MEarth, so that Earth and Venus are near the maximum size for rocky planets.[163]

The composition of Earth's atmosphere is different from the other planets because the various life processes that have transpired on the planet have introduced free molecular oxygen.[227] The atmospheres of Mars and Venus are both dominated by carbon dioxide, but differ drastically in density: the average surface pressure of Mars' atmosphere is less than 1% that of Earth's (too low to allow liquid water to exist),[228] while the average surface pressure of Venus' atmosphere is about 92 times that of Earth's.[229] It is likely that Venus' atmosphere was the result of a runaway greenhouse effect in its history, which today makes it the hottest planet by surface temperature, hotter even than Mercury.[230] Despite hostile surface conditions, temperature and pressure at about 50–55 km altitude in Venus' atmosphere are close to Earthlike conditions (the only place in the Solar System beyond Earth where this is so) and this region has been suggested as a plausible base for future human exploration.[231] Titan has the only nitrogen-rich planetary atmosphere in the Solar System other than Earth's. Just as Earth's conditions are close to the triple point of water, allowing it to exist in all three states on the planet's surface, so Titan's are to the triple point of methane.[232]

Planetary atmospheres are affected by the varying insolation or internal energy, leading to the formation of dynamic weather systems such as hurricanes (on Earth), planet-wide dust storms (on Mars), a greater-than-Earth-sized anticyclone on Jupiter (called the Great Red Spot), and holes in the atmosphere (on Neptune).[177] Weather patterns detected on exoplanets include a hot region on HD 189733 b twice the size of the Great Red Spot,[233] as well as clouds on the hot Jupiter Kepler-7b,[234] the super-Earth Gliese 1214 b and others.[235][236]

Hot Jupiters, due to their extreme proximities to their host stars, have been shown to be losing their atmospheres into space due to stellar radiation, much like the tails of comets.[237][238] These planets may have vast differences in temperature between their day and night sides that produce supersonic winds,[239] although multiple factors are involved and the details of the atmospheric dynamics that affect the day-night temperature difference are complex.[240][241]


Main article: Magnetosphere

Earth's magnetosphere (diagram)

One important characteristic of the planets is their intrinsic magnetic moments, which in turn give rise to magnetospheres. The presence of a magnetic field indicates that the planet is still geologically alive. In other words, magnetized planets have flows of electrically conducting material in their interiors, which generate their magnetic fields. These fields significantly change the interaction of the planet and solar wind. A magnetized planet creates a cavity in the solar wind around itself called the magnetosphere, which the wind cannot penetrate. The magnetosphere can be much larger than the planet itself. In contrast, non-magnetized planets have only small magnetospheres induced by interaction of the ionosphere with the solar wind, which cannot effectively protect the planet.[242]

Of the eight planets in the Solar System, only Venus and Mars lack such a magnetic field.[242] Of the magnetized planets the magnetic field of Mercury is the weakest, and is barely able to deflect the solar wind. Jupiter's moon Ganymede has a magnetic field several times stronger, and Jupiter's is the strongest in the Solar System (so intense in fact that it poses a serious health risk to future crewed missions to all its moons inward of Callisto[243]). The magnetic fields of the other giant planets, measured at their surfaces, are roughly similar in strength to that of Earth, but their magnetic moments are significantly larger. The magnetic fields of Uranus and Neptune are strongly tilted relative to the planets' rotational axes and displaced from the planets' centres.[242]

In 2003, a team of astronomers in Hawaii observing the star HD 179949 detected a bright spot on its surface, apparently created by the magnetosphere of an orbiting hot Jupiter.[244][245]

Secondary characteristics

Main articles: Natural satellite and planetary ring

The rings of Saturn

Several planets or dwarf planets in the Solar System (such as Neptune and Pluto) have orbital periods that are in resonance with each other or with smaller bodies. This is common in satellite systems (e.g. the resonance between Io, Europa, and Ganymede around Jupiter, or between Enceladus and Dione around Saturn). All except Mercury and Venus have natural satellites, often called "moons". Earth has one, Mars has two, and the giant planets have numerous moons in complex planetary-type systems. Except for Ceres and Sedna, all the consensus dwarf planets are known to have at least one moon as well. Many moons of the giant planets have features similar to those on the terrestrial planets and dwarf planets, and some have been studied as possible abodes of life (especially Europa and Enceladus).[246][247][248][249][250]

The four giant planets are orbited by planetary rings of varying size and complexity. The rings are composed primarily of dust or particulate matter, but can host tiny 'moonlets' whose gravity shapes and maintains their structure. Although the origins of planetary rings is not precisely known, they are believed to be the result of natural satellites that fell below their parent planet's Roche limit and were torn apart by tidal forces.[251][252] The dwarf planets Haumea[253] and Quaoar also have rings.[254]

No secondary characteristics have been observed around extrasolar planets. The sub-brown dwarf Cha 110913-773444, which has been described as a rogue planet, is believed to be orbited by a tiny protoplanetary disc[255] and the sub-brown dwarf OTS 44 was shown to be surrounded by a substantial protoplanetary disk of at least 10 Earth masses.[256]

See also

A photomontage of the eight planets and the MoonNeptune in fictionUranus in fictionSaturn in fictionJupiter in fictionMars in fictionEarth in science fictionMoon in science fictionVenus in fictionMercury in fiction
Clicking on a planet leads to the article about its depiction in fiction.


  1. ^ Margot's parameter[66] is not to be confused with the famous mathematical constant π≈3.14159265 ... .
  2. ^ In Korean, these names are more often written in Hangul rather than Chinese characters, e.g. 명왕성 for Pluto. In Vietnamese, calques are more common than directly reading these names as Sino-Vietnamese, e.g. sao Thuỷ rather than Thuỷ tinh for Mercury. Pluto is not sao Minh Vương but sao Diêm Vương "Yama star".[87]
  3. ^ Here, "Earth-sized" means 1–2 Earth radii, and "habitable zone" means the region with 0.25 to 4 times Earth's stellar flux (corresponding to 0.5–2 AU for the Sun). Data for G-type stars like the Sun is not available. This statistic is an extrapolation from data on K-type stars.[160][161]


  1. ^ a b c d "IAU 2006 General Assembly: Result of the IAU Resolution votes". International Astronomical Union. 2006. Retrieved 30 December 2009.
  2. ^ "Working Group on Extrasolar Planets (WGESP) of the International Astronomical Union". IAU. 2001. Archived from the original on 16 September 2006. Retrieved 23 August 2008.
  3. ^ a b c d e f g Lakdawalla, Emily (21 April 2020). "What Is A Planet?". The Planetary Society. Archived from the original on 22 January 2022. Retrieved 3 April 2022.
  4. ^ Grossman, Lisa (24 August 2021). "The definition of planet is still a sore point – especially among Pluto fans". Science News.
  5. ^ "What is a Planet? | Planets". NASA Solar System Exploration. Retrieved 2 May 2022.
  6. ^ a b c d Hilton, James L. (17 September 2001). "When Did the Asteroids Become Minor Planets?". U.S. Naval Observatory. Archived from the original on 21 September 2007. Retrieved 8 April 2007.
  7. ^ a b c d e f g h Metzger, Philip T.; Grundy, W. M.; Sykes, Mark V.; Stern, Alan; Bell III, James F.; Detelich, Charlene E.; Runyon, Kirby; Summers, Michael (2022). "Moons are planets: Scientific usefulness versus cultural teleology in the taxonomy of planetary science". Icarus. 374: 114768. arXiv:2110.15285. Bibcode:2022Icar..37414768M. doi:10.1016/j.icarus.2021.114768. S2CID 240071005. Retrieved 8 August 2022.
  8. ^ "Ancient Greek Astronomy and Cosmology". The Library of Congress. Retrieved 19 May 2016.
  9. ^ πλάνης, πλανήτης. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project Retrieved on 11 July 2022.
  10. ^ "Definition of planet". Merriam-Webster OnLine. Retrieved 23 July 2007.
  11. ^ "Planet Etymology". Retrieved 29 June 2015.
  12. ^ a b "planet, n". Oxford English Dictionary. 2007. Retrieved 7 February 2008. Note: select the Etymology tab
  13. ^ Neugebauer, Otto E. (1945). "The History of Ancient Astronomy Problems and Methods". Journal of Near Eastern Studies. 4 (1): 1–38. doi:10.1086/370729. S2CID 162347339.
  14. ^ Ronan, Colin (1996). "Astronomy Before the Telescope". In Walker, Christopher (ed.). Astronomy in China, Korea and Japan. British Museum Press. pp. 264–265.
  15. ^ Kuhn, Thomas S. (1957). The Copernican Revolution. Harvard University Press. pp. 5–20. ISBN 978-0-674-17103-9.
  16. ^ a b Frautschi, Steven C.; Olenick, Richard P.; Apostol, Tom M.; Goodstein, David L. (2007). The Mechanical Universe: Mechanics and Heat (Advanced ed.). Cambridge [Cambridgeshire]: Cambridge University Press. p. 58. ISBN 978-0-521-71590-4. OCLC 227002144.
  17. ^ a b c d e Evans, James (1998). The History and Practice of Ancient Astronomy. Oxford University Press. pp. 296–297. ISBN 978-0-19-509539-5. Retrieved 4 February 2008.
  18. ^ Rochberg, Francesca (2000). "Astronomy and Calendars in Ancient Mesopotamia". In Jack Sasson (ed.). Civilizations of the Ancient Near East. Vol. III. p. 1930.
  19. ^ Aaboe, Asger (1991), "The culture of Babylonia: Babylonian mathematics, astrology, and astronomy", in Boardman, John; Edwards, I. E. S.; Hammond, N. G. L.; Sollberger, E.; Walker, C. B. F (eds.), The Assyrian and Babylonian Empires and other States of the Near East, from the Eighth to the Sixth Centuries B.C., The Cambridge Ancient History, vol. 3, Cambridge: Cambridge University Press, pp. 276–292, ISBN 978-0521227179
  20. ^ Hermann Hunger, ed. (1992). Astrological reports to Assyrian kings. State Archives of Assyria. Vol. 8. Helsinki University Press. ISBN 978-951-570-130-5.
  21. ^ Lambert, W. G.; Reiner, Erica (1987). "Babylonian Planetary Omens. Part One. Enuma Anu Enlil, Tablet 63: The Venus Tablet of Ammisaduqa". Journal of the American Oriental Society. 107 (1): 93–96. doi:10.2307/602955. JSTOR 602955.
  22. ^ Kasak, Enn; Veede, Raul (2001). Mare Kõiva; Andres Kuperjanov (eds.). "Understanding Planets in Ancient Mesopotamia" (PDF). Electronic Journal of Folklore. 16: 7–35. CiteSeerX doi:10.7592/fejf2001.16.planets. Retrieved 6 February 2008.
  23. ^ Sachs, A. (2 May 1974). "Babylonian Observational Astronomy". Philosophical Transactions of the Royal Society. 276 (1257): 43–50 [45 & 48–49]. Bibcode:1974RSPTA.276...43S. doi:10.1098/rsta.1974.0008. JSTOR 74273. S2CID 121539390.
  24. ^ Burnet, John (1950). Greek philosophy: Thales to Plato. Macmillan and Co. pp. 7–11. ISBN 978-1-4067-6601-1. Retrieved 7 February 2008.
  25. ^ Cooley, Jeffrey L. (2008). "Inana and Šukaletuda: A Sumerian Astral Myth". KASKAL. 5: 161–172. ISSN 1971-8608. The Greeks, for example, originally identified the morning and evening stars with two separate deities, Phosphoros and Hesporos respectively. In Mesopotamia, it seems that this was recognized prehistorically. Assuming its authenticity, a cylinder seal from the Erlenmeyer collection attests to this knowledge in southern Iraq as early as the Late Uruk / Jemdet Nasr Period, as do the archaic texts of the period. [...] Whether or not one accepts the seal as authentic, the fact that there is no epithetical distinction between the morning and evening appearances of Venus in any later Mesopotamian literature attests to a very, very early recognition of the phenomenon.
  26. ^ Kurtik, G. E. (June 1999). "The identification of Inanna with the planet Venus: A criterion for the time determination of the recognition of constellations in ancient Mesopotamia". Astronomical & Astrophysical Transactions. 17 (6): 501–513. Bibcode:1999A&AT...17..501K. doi:10.1080/10556799908244112. ISSN 1055-6796.
  27. ^ a b Goldstein, Bernard R. (1997). "Saving the phenomena: the background to Ptolemy's planetary theory". Journal for the History of Astronomy. 28 (1): 1–12. Bibcode:1997JHA....28....1G. doi:10.1177/002182869702800101. S2CID 118875902.
  28. ^ Ptolemy; Toomer, G. J. (1998). Ptolemy's Almagest. Princeton University Press. ISBN 978-0-691-00260-6.
  29. ^ O'Connor, J. J.; Robertson, E. F. "Aryabhata the Elder". MacTutor History of Mathematics archive. Retrieved 10 July 2022.
  30. ^ Sarma, K. V. (1997). "Astronomy in India". In Selin, Helaine (ed.). Encyclopaedia of the History of Science, Technology, and Medicine in Non-Western Cultures. Kluwer Academic Publishers. p. 116. ISBN 0-7923-4066-3.
  31. ^ Bausani, Alessandro (1973). "Cosmology and Religion in Islam". Scientia/Rivista di Scienza. 108 (67): 762.
  32. ^ Ragep, Sally P. (2007). "Ibn Sina, Abu Ali [known as Avicenna] (980?1037)". In Thomas Hockey (ed.). Ibn Sīnā: Abū ʿAlī al-Ḥusayn ibn ʿAbdallāh ibn Sīnā. The Biographical Encyclopedia of Astronomers. Springer Science+Business Media. pp. 570–572. Bibcode:2000eaa..bookE3736.. doi:10.1888/0333750888/3736. ISBN 978-0-333-75088-9.
  33. ^ Huth, John Edward (2013). The Lost Art of Finding Our Way. Harvard University Press. pp. 216–217. ISBN 978-0-674-07282-4.
  34. ^ a b Van Helden, Al (1995). "Copernican System". The Galileo Project. Rice University. Retrieved 28 January 2008.
  35. ^ Dreyer, J. L. E. (1912). The Scientific Papers of Sir William Herschel. Vol. 1. Royal Society and Royal Astronomical Society. p. 100.
  36. ^ "asteroid". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  37. ^ a b Metzger, Philip T.; Sykes, Mark V.; Stern, Alan; Runyon, Kirby (2019). "The Reclassification of Asteroids from Planets to Non-Planets". Icarus. 319: 21–32. arXiv:1805.04115. Bibcode:2019Icar..319...21M. doi:10.1016/j.icarus.2018.08.026. S2CID 119206487.
  38. ^ Baum, Richard P.; Sheehan, William (2003). In Search of Planet Vulcan: The Ghost in Newton's Clockwork. Basic Books. p. 264. ISBN 978-0738208893.
  39. ^ Park, Ryan S.; Folkner, William M.; Konopliv, Alexander S.; Williams, James G.; et al. (2017). "Precession of Mercury's Perihelion from Ranging to the MESSENGER Spacecraft". The Astronomical Journal. 153 (3): 121. Bibcode:2017AJ....153..121P. doi:10.3847/1538-3881/aa5be2. hdl:1721.1/109312. S2CID 125439949.
  40. ^ Croswell, Ken (1997). Planet Quest: The Epic Discovery of Alien Solar Systems. The Free Press. p. 57. ISBN 978-0-684-83252-4.
  41. ^ Lyttleton, Raymond A. (1936). "On the possible results of an encounter of Pluto with the Neptunian system". Monthly Notices of the Royal Astronomical Society. 97 (2): 108–115. Bibcode:1936MNRAS..97..108L. doi:10.1093/mnras/97.2.108.
  42. ^ Whipple, Fred (1964). "The History of the Solar System". Proceedings of the National Academy of Sciences of the United States of America. 52 (2): 565–594. Bibcode:1964PNAS...52..565W. doi:10.1073/pnas.52.2.565. PMC 300311. PMID 16591209.
  43. ^ Christy, James W.; Harrington, Robert Sutton (1978). "The Satellite of Pluto". Astronomical Journal. 83 (8): 1005–1008. Bibcode:1978AJ.....83.1005C. doi:10.1086/112284. S2CID 120501620.
  44. ^ Luu, Jane X.; Jewitt, David C. (1996). "The Kuiper Belt". Scientific American. 274 (5): 46–52. Bibcode:1996SciAm.274e..46L. doi:10.1038/scientificamerican0596-46.
  45. ^ a b "Pluto loses status as a planet". BBC News. British Broadcasting Corporation. 24 August 2006. Retrieved 23 August 2008.
  46. ^ a b Wolszczan, A.; Frail, D. A. (1992). "A planetary system around the millisecond pulsar PSR1257 + 12". Nature. 355 (6356): 145–147. Bibcode:1992Natur.355..145W. doi:10.1038/355145a0. S2CID 4260368.
  47. ^ Mayor, Michel; Queloz, Didier (1995). "A Jupiter-mass companion to a solar-type star". Nature. 378 (6356): 355–359. Bibcode:1995Natur.378..355M. doi:10.1038/378355a0. S2CID 4339201.
  48. ^ Basri, Gibor (2000). "Observations of Brown Dwarfs". Annual Review of Astronomy and Astrophysics. 38 (1): 485–519. Bibcode:2000ARA&A..38..485B. doi:10.1146/annurev.astro.38.1.485.
  49. ^ a b c d Basri, Gibor; Brown, Michael E. (2006). "Planetesimals to Brown Dwarfs: What is a Planet?" (PDF). Annual Review of Earth and Planetary Sciences. 34: 193–216. arXiv:astro-ph/0608417. Bibcode:2006AREPS..34..193B. doi:10.1146/ S2CID 119338327. Retrieved 4 August 2008.
  50. ^ Boss, Alan P.; Basri, Gibor; Kumar, Shiv S.; Liebert, James; Martín, Eduardo L.; Reipurth, Bo; Zinnecker, Hans (2003), "Nomenclature: Brown Dwarfs, Gas Giant Planets, and ?", Brown Dwarfs, 211: 529, Bibcode:2003IAUS..211..529B
  51. ^ "Estados Unidos "conquista" Haumea". ABC (in Spanish). 20 September 2008. Retrieved 18 September 2008.
  52. ^ Brown, Michael E. "The Dwarf Planets". California Institute of Technology, Department of Geological Sciences. Retrieved 26 January 2008.
  53. ^ Brown, Mike (23 February 2021). "How Many Dwarf Planets Are There in the Outer Solar System?". California Institute of Technology. Archived from the original on 19 July 2022. Retrieved 11 August 2022.
  54. ^ Green, D. W. E. (13 September 2006). "(134340) Pluto, (136199) Eris, and (136199) Eris I (Dysnomia)" (PDF). IAU Circular. Central Bureau for Astronomical Telegrams, International Astronomical Union. 8747: 1. Bibcode:2006IAUC.8747....1G. Circular No. 8747. Archived from the original on 24 June 2008. Retrieved 5 July 2011.
  55. ^ Stern, S. Alan; Levison, Harold F. (2002), Rickman, H. (ed.), "Regarding the criteria for planethood and proposed planetary classification schemes", Highlights of Astronomy, San Francisco: Astronomical Society of the Pacific, 12: 205–213, Bibcode:2002HiA....12..205S, doi:10.1017/S1539299600013289, ISBN 978-1-58381-086-6 See p. 208.
  56. ^ Runyon, Kirby D.; Stern, S. Alan (17 May 2018). "An organically grown planet definition — Should we really define a word by voting?". Astronomy. Retrieved 12 October 2019.
  57. ^ a b c d e Grundy, W.M.; Noll, K.S.; Buie, M.W.; Benecchi, S.D.; et al. (December 2018). "The Mutual Orbit, Mass, and Density of Transneptunian Binary Gǃkúnǁʼhòmdímà ((229762) 2007 UK126)" (PDF). Icarus. doi:10.1016/j.icarus.2018.12.037. S2CID 126574999. Archived from the original on 7 April 2019.
  58. ^ Raymond, C. A.; Ermakov, A. I.; Castillo-Rogez, J. C.; Marchi, S.; et al. (August 2020). "Impact-driven mobilization of deep crustal brines on dwarf planet Ceres". Nature Astronomy. 4 (8): 741–747. Bibcode:2020NatAs...4..741R. doi:10.1038/s41550-020-1168-2. ISSN 2397-3366. S2CID 211137608.
  59. ^ Barr, Amy C.; Schwamb, Megan E. (1 August 2016). "Interpreting the densities of the Kuiper belt's dwarf planets". Monthly Notices of the Royal Astronomical Society. 460 (2): 1542–1548. doi:10.1093/mnras/stw1052. ISSN 0035-8711.
  60. ^ Villard, Ray (14 May 2010). "Should Large Moons Be Called 'Satellite Planets'?". Discovery News. Discovery, Inc. Archived from the original on 5 May 2012. Retrieved 4 November 2011.
  61. ^ Urrutia, Doris Elin (28 October 2019). "Asteroid Hygiea May be the Smallest Dwarf Planet in the Solar System". Purch Group.
  62. ^ "The solar system may have a new smallest dwarf planet: Hygiea". Science News. Society for Science. 28 October 2019.
  63. ^ a b Yang, B.; Hanuš, J.; Carry, B.; Vernazza, P.; Brož, M.; Vachier, F.; Rambaux, N.; Marsset, M.; Chrenko, O.; Ševeček, P.; Viikinkoski, M.; Jehin, E.; Ferrais, M.; Podlewska-Gaca, E.; Drouard, A.; Marchis, F.; Birlan, M.; Benkhaldoun, Z.; Berthier, J.; Bartczak, P.; Dumas, C.; Dudziński, G.; Ďurech, J.; Castillo-Rogez, J.; Cipriani, F.; Colas, F.; Fetick, R.; Fusco, T.; Grice, J.; et al. (2020), "Binary asteroid (31) Euphrosyne: Ice-rich and nearly spherical", Astronomy & Astrophysics, 641: A80, arXiv:2007.08059, Bibcode:2020A&A...641A..80Y, doi:10.1051/0004-6361/202038372, S2CID 220546126
  64. ^ a b Lecavelier des Etangs, A.; Lissauer, Jack J. (1 June 2022). "The IAU working definition of an exoplanet". New Astronomy Reviews. 94: 101641. arXiv:2203.09520. Bibcode:2022NewAR..9401641L. doi:10.1016/j.newar.2022.101641. ISSN 1387-6473. S2CID 247065421.
  65. ^ Netburn, Deborah (13 November 2015). "Why we need a new definition of the word 'planet'". Los Angeles Times.
  66. ^ a b Margot, Jean-Luc (2015). "A quantitative criterion for defining planets". The Astronomical Journal. 150 (6): 185. arXiv:1507.06300. Bibcode:2015AJ....150..185M. doi:10.1088/0004-6256/150/6/185. S2CID 51684830.
  67. ^ Rincon, Paul (16 August 2006). "Planets plan boosts tally 12". BBC News. British Broadcasting Corporation. Retrieved 23 August 2008.
  68. ^ Soter, Steven (2006). "What is a planet?". Astronomical Journal. 132 (6): 2513–2519. arXiv:astro-ph/0608359. Bibcode:2006AJ....132.2513S. doi:10.1086/508861. S2CID 14676169.
  69. ^ a b c d Lecavelier des Etangs, A.; Lissauer, Jack J. (2022). "The IAU working definition of an exoplanet". New Astronomy Reviews. 94: 101641. arXiv:2203.09520. Bibcode:2022NewAR..9401641L. doi:10.1016/j.newar.2022.101641. S2CID 247065421.
  70. ^ a b c "Official Working Definition of an Exoplanet". IAU position statement. Retrieved 29 November 2020.
  71. ^ Brown, Michael E.; Butler, Bryan (July 2023). "Masses and densities of dwarf planet satellites measured with ALMA". The Planetary Science Journal. in press: 11. arXiv:2307.04848.
  72. ^ Huxley, Margaret (2000). "The Gates and Guardians in Sennacherib's Addition to the Temple of Assur". Iraq. 62: 109–137. doi:10.2307/4200484. ISSN 0021-0889. JSTOR 4200484. S2CID 191393468.
  73. ^ Wiggermann, Frans A. M. (1998). "Nergal A. Philological". Reallexikon der Assyriologie. Bavarian Academy of Sciences and Humanities. Retrieved 12 July 2022.
  74. ^ Koch, Ulla Susanne (1995). Mesopotamian Astrology: An Introduction to Babylonian and Assyrian Celestial Divination. Museum Tusculanum Press. pp. 128–129. ISBN 978-87-7289-287-0.
  75. ^ Cecilia, Ludovica (6 November 2019). "A Late Composition Dedicated to Nergal". Altorientalische Forschungen. 46 (2): 204–213. doi:10.1515/aofo-2019-0014. hdl:1871.1/f23ff882-1539-4906-bc08-049906f8d505. ISSN 2196-6761. S2CID 208269607.
  76. ^ Rengel, Marian; Daly, Kathleen N. (2009). Greek and Roman Mythology, A to Z Archived 29 December 2022 at the Wayback Machine. United States: Facts On File, Incorporated. p. 66.
  77. ^ Zerubavel, Eviatar (1989). The Seven Day Circle: The history and meaning of the week. University of Chicago Press. p. 14. ISBN 978-0-226-98165-9. Retrieved 7 February 2008.
  78. ^ a b Falk, Michael; Koresko, Christopher (2004). "Astronomical names for the days of the week". Journal of the Royal Astronomical Society of Canada. 93: 122–133. arXiv:astro-ph/0307398. Bibcode:1999JRASC..93..122F. doi:10.1016/j.newast.2003.07.002. S2CID 118954190.
  79. ^ Ross, Margaret Clunies (January 2018). "Explainer: the gods behind the days of the week". The Conversation. Retrieved 13 May 2022.
  80. ^ "earth". Oxford English Dictionary. Retrieved 7 May 2021.
  81. ^ Harper, Douglas (September 2001). "Etymology of "terrain"". Online Etymology Dictionary. Retrieved 30 January 2008.
  82. ^ Kambas, Michael (2004). Greek-English, English-Greek Dictionary. Hippocrene Books. p. 259. ISBN 978-0781810029.
  83. ^ Markel, Stephen Allen (1989). The Origin and Early Development of the Nine Planetary Deities (Navagraha) (PhD). University of Michigan. Retrieved 11 August 2022.
  84. ^ Panaino, Antonio (20 September 2016). "Planets". Encyclopædia Iranica.
  85. ^ a b 卞毓麟 [Bian Yulin] (2007). ""阋神星"的来龙去脉" (PDF). 中国科技术语 [China Terminology] (in Chinese (China)). 9 (4): 59–61. doi:10.3969/j.issn.1673-8578.2007.04.020. Retrieved 21 September 2022.
  86. ^ "Planetary linguistics". Archived from the original on 7 April 2010. Retrieved 8 April 2010.
  87. ^ "Cambridge English-Vietnamese Dictionary". Archived from the original on 7 October 2022. Retrieved 21 September 2022.
  88. ^ 李竞 [Li Jing] (2018). "小行星世界中的古典音乐". 中国科技术语 [China Terminology]. 20 (3): 66–75. doi:10.3969/j.issn.1673-8578.2018.03.015. Retrieved 5 May 2023.
  89. ^ a b Stieglitz, Robert (April 1981). "The Hebrew names of the seven planets". Journal of Near Eastern Studies. 40 (2): 135–137. doi:10.1086/372867. JSTOR 545038. S2CID 162579411.
  90. ^ Ettinger, Yair (31 December 2009). "Uranus and Neptune Get Hebrew Names at Last". Haaretz. Retrieved 5 October 2022.
  91. ^ Zucker, Shay (2011). "Hebrew names of the planets". The Role of Astronomy in Society and Culture, Proceedings of the International Astronomical Union, IAU Symposium. 260: 301–305. Bibcode:2011IAUS..260..301Z. doi:10.1017/S1743921311002432. S2CID 162671357.
  92. ^ Ragep, F.J.; Hartner, W. (24 April 2012). "Zuhara". Encyclopaedia of Islam (2nd ed.) – via
  93. ^ Meyers, Carol L.; O'Connor, M.; O'Connor, Michael Patrick (1983). The Word of the Lord Shall Go Forth: Essays in honor of David Noel Freedman in celebration of his sixtieth birthday. Eisenbrauns. ISBN 978-0931464195 – via Google Books.
  94. ^ Eilers, Wilhelm (1976). Sinn und Herkunft der Planetennamen (PDF). Munich: Bavarian Academy of Sciences and Humanities.
  95. ^ Galter, Hannes D. (23–27 September 1991). "Die Rolle der Astronomie in den Kulturen Mesopotamiens" [The role of astronomy in the cultures of the Mesopotamians]. Beiträge Zum 3. Grazer Morgenländischen Symposion (23–27 September 1991). 3. Grazer Morgenländischen Symposion [Third Graz Oriental Symposium]. Graz, Austria: GrazKult (published 31 July 1993). ISBN 978-3853750094 – via Google Books.
  96. ^ al-Masūdī (1841). "El-Masūdī's Historical Encyclopaedia, entitled "Meadows of Gold and Mines of Gems."". Oriental Translation Fund of Great Britain and Ireland – via Google Books.
  97. ^ Ali-Abu'l-Hassan, Mas'ûdi (1841). "Historical Encyclopaedia: Entitled "Meadows of gold and mines of gems"". Printed for the Oriental Translation Fund of Great Britain and Ireland – via Google Books.
  98. ^ Schmadel, Lutz (2012). Dictionary of Minor Planet Names (6th ed.). Springer. p. 15. ISBN 978-3642297182.
  99. ^ "Minor Planet Naming Guidelines (Rules and Guidelines for naming non-cometary small Solar-System bodies) – v1.0" (PDF). Working Group Small Body Nomenclature (PDF). 20 December 2021.
  100. ^ "IAU: WG Small Body Nomenclature (WGSBN)". Working Group Small Body Nomenclature. Retrieved 9 February 2022.
  101. ^ Lassell, W. (1852). "Beobachtungen der Uranus-Satelliten". Astronomische Nachrichten. 34: 325. Bibcode:1852AN.....34..325.
  102. ^ "Gazetteer of Planetary Nomenclature". IAU. Retrieved 27 June 2022.
  103. ^ a b Jones, Alexander (1999). Astronomical Papyri from Oxyrhynchus. pp. 62–63. ISBN 978-0-87169-233-7.
  104. ^ "Bianchini's planisphere". Florence, Italy: Istituto e Museo di Storia della Scienza [Institute and Museum of the History of Science]. Archived from the original on 27 February 2018. Retrieved 20 August 2018.
  105. ^ a b Maunder, A.S.D. (1934). "The origin of the symbols of the planets". The Observatory. Vol. 57. pp. 238–247. Bibcode:1934Obs....57..238M.
  106. ^ Mattison, Hiram (1872). High-School Astronomy. Sheldon & Co. pp. 32–36.
  107. ^ a b Iancu, Laurentiu (14 August 2009). "Proposal to Encode the Astronomical Symbol for Uranus" (PDF).
  108. ^ Bode, J.E. (1784). Von dem neu entdeckten Planeten. Beim Verfaszer. pp. 95–96.
  109. ^ a b Gould, B.A. (1850). Report on the history of the discovery of Neptune. Smithsonian Institution. pp. 5, 22.
  110. ^ Francisca Herschel (August 1917). "The meaning of the symbol H+o for the planet Uranus". The Observatory. 40: 306. Bibcode:1917Obs....40..306H.
  111. ^ "NASA's Solar System Exploration: Multimedia: Gallery: Pluto's Symbol". NASA. Archived from the original on 1 October 2006. Retrieved 29 November 2011.
  112. ^ a b c d Miller, Kirk (26 October 2021). "Unicode request for dwarf-planet symbols" (PDF).
  113. ^ The IAU Style Manual (PDF). 1989. p. 27.
  114. ^ Anderson, Deborah (4 May 2022). "Out of this World: New Astronomy Symbols Approved for the Unicode Standard". The Unicode Consortium. Retrieved 6 August 2022.
  115. ^ Wetherill, G. W. (1980). "Formation of the Terrestrial Planets". Annual Review of Astronomy and Astrophysics. 18 (1): 77–113. Bibcode:1980ARA&A..18...77W. doi:10.1146/annurev.aa.18.090180.000453.
  116. ^ D'Angelo, G.; Bodenheimer, P. (2013). "Three-dimensional Radiation-hydrodynamics Calculations of the Envelopes of Young Planets Embedded in Protoplanetary Disks". The Astrophysical Journal. 778 (1): 77 (29 pp.). arXiv:1310.2211. Bibcode:2013ApJ...778...77D. doi:10.1088/0004-637X/778/1/77. S2CID 118522228.
  117. ^ Inaba, S.; Ikoma, M. (2003). "Enhanced Collisional Growth of a Protoplanet that has an Atmosphere". Astronomy and Astrophysics. 410 (2): 711–723. Bibcode:2003A&A...410..711I. doi:10.1051/0004-6361:20031248.
  118. ^ D'Angelo, G.; Weidenschilling, S. J.; Lissauer, J. J.; Bodenheimer, P. (2014). "Growth of Jupiter: Enhancement of core accretion by a voluminous low-mass envelope". Icarus. 241: 298–312. arXiv:1405.7305. Bibcode:2014Icar..241..298D. doi:10.1016/j.icarus.2014.06.029. S2CID 118572605.
  119. ^ Lissauer, J. J.; Hubickyj, O.; D'Angelo, G.; Bodenheimer, P. (2009). "Models of Jupiter's growth incorporating thermal and hydrodynamic constraints". Icarus. 199 (2): 338–350. arXiv:0810.5186. Bibcode:2009Icar..199..338L. doi:10.1016/j.icarus.2008.10.004. S2CID 18964068.
  120. ^ D'Angelo, G.; Durisen, R. H.; Lissauer, J. J. (2011). "Giant Planet Formation". In Seager, S. (ed.). Exoplanets. University of Arizona Press, Tucson, AZ. pp. 319–346. arXiv:1006.5486.
  121. ^ Chambers, J. (2011). "Terrestrial Planet Formation". In Seager, S. (ed.). Exoplanets. Tucson, AZ: University of Arizona Press. pp. 297–317.
  122. ^ Canup, Robin M.; Ward, William R. (2008). Origin of Europa and the Galilean Satellites. University of Arizona Press. p. 59. arXiv:0812.4995. ISBN 978-0-8165-2844-8.
  123. ^ D'Angelo, G.; Podolak, M. (2015). "Capture and Evolution of Planetesimals in Circumjovian Disks". The Astrophysical Journal. 806 (1): 29pp. arXiv:1504.04364. Bibcode:2015ApJ...806..203D. doi:10.1088/0004-637X/806/2/203. S2CID 119216797.
  124. ^ Agnor, C. B.; Hamilton, D. P. (2006). "Neptune's capture of its moon Triton in a binary–planet gravitational encounter" (PDF). Nature. 441 (7090): 192–4. Bibcode:2006Natur.441..192A. doi:10.1038/nature04792. PMID 16688170. S2CID 4420518. Archived from the original (PDF) on 14 October 2016. Retrieved 1 May 2022.
  125. ^ Taylor, G. Jeffrey (31 December 1998). "Origin of the Earth and Moon". Planetary Science Research Discoveries. Hawai'i Institute of Geophysics and Planetology. Archived from the original on 10 June 2010. Retrieved 7 April 2010.
  126. ^ Stern, S.A.; Bagenal, F.; Ennico, K.; Gladstone, G.R.; et al. (16 October 2015). "The Pluto system: Initial results from its exploration by New Horizons". Science. 350 (6258): aad1815. arXiv:1510.07704. Bibcode:2015Sci...350.1815S. doi:10.1126/science.aad1815. PMID 26472913. S2CID 1220226.
  127. ^ Dutkevitch, Diane (1995). The Evolution of Dust in the Terrestrial Planet Region of Circumstellar Disks Around Young Stars (PhD thesis). University of Massachusetts Amherst. Bibcode:1995PhDT..........D. Archived from the original on 25 November 2007. Retrieved 23 August 2008.
  128. ^ Matsuyama, I.; Johnstone, D.; Murray, N. (2005). "Halting Planet Migration by Photoevaporation from the Central Source". The Astrophysical Journal. 585 (2): L143–L146. arXiv:astro-ph/0302042. Bibcode:2003ApJ...585L.143M. doi:10.1086/374406. S2CID 16301955.
  129. ^ Kenyon, Scott J.; Bromley, Benjamin C. (2006). "Terrestrial Planet Formation. I. The Transition from Oligarchic Growth to Chaotic Growth". Astronomical Journal. 131 (3): 1837–1850. arXiv:astro-ph/0503568. Bibcode:2006AJ....131.1837K. doi:10.1086/499807. S2CID 15261426.
  130. ^ Martin, R. G.; Livio, M. (1 January 2013). "On the formation and evolution of asteroid belts and their potential significance for life". Monthly Notices of the Royal Astronomical Society: Letters. 428 (1): L11–L15. doi:10.1093/mnrasl/sls003. ISSN 1745-3925.
  131. ^ Peale, S. J. (September 1999). "Origin and Evolution of the Natural Satellites". Annual Review of Astronomy and Astrophysics. 37 (1): 533–602. Bibcode:1999ARA&A..37..533P. doi:10.1146/annurev.astro.37.1.533. ISSN 0066-4146. Archived from the original on 13 May 2022. Retrieved 13 May 2022.
  132. ^ Ida, Shigeru; Nakagawa, Yoshitsugu; Nakazawa, Kiyoshi (1987). "The Earth's core formation due to the Rayleigh-Taylor instability". Icarus. 69 (2): 239–248. Bibcode:1987Icar...69..239I. doi:10.1016/0019-1035(87)90103-5.
  133. ^ Kasting, James F. (1993). "Earth's early atmosphere". Science. 259 (5097): 920–926. Bibcode:1993Sci...259..920K. doi:10.1126/science.11536547. PMID 11536547. S2CID 21134564.
  134. ^ Chuang, F. (6 June 2012). "FAQ – Atmosphere". Planetary Science Institute. Retrieved 13 May 2022.
  135. ^ Fischer, Debra A.; Valenti, Jeff (2005). "The Planet-Metallicity Correlation". The Astrophysical Journal. 622 (2): 1102. Bibcode:2005ApJ...622.1102F. doi:10.1086/428383.
  136. ^ Wang, Ji; Fischer, Debra A. (2013). "Revealing a Universal Planet-Metallicity Correlation for Planets of Different Sizes Around Solar-Type Stars". The Astronomical Journal. 149 (1): 14. arXiv:1310.7830. Bibcode:2015AJ....149...14W. doi:10.1088/0004-6256/149/1/14. S2CID 118415186.
  137. ^ Harrison, Edward Robert (2000). Cosmology: The Science of the Universe. Cambridge University Press. p. 114. ISBN 978-0-521-66148-5.
  138. ^ a b c "Planetary Physical Parameters". Solar System Dynamics. Jet Propulsion Laboratory. Retrieved 11 July 2022.
  139. ^ a b Lewis, John S. (2004). Physics and Chemistry of the Solar System (2nd ed.). Academic Press. p. 59. ISBN 978-0-12-446744-6.
  140. ^ a b Marley, Mark (2 April 2019). "Not a Heart of Ice". The Planetary Society. Retrieved 5 May 2022.
  141. ^ Brown, Michael E.; Schaller, Emily L. (15 June 2007). "The Mass of Dwarf Planet Eris" (PDF). Science. 316 (5831): 1585. Bibcode:2007Sci...316.1585B. doi:10.1126/science.1139415. PMID 17569855. S2CID 21468196. Archived from the original (PDF) on 4 March 2016. Retrieved 27 September 2015.
  142. ^ "How Big Is Pluto? New Horizons Settles Decades-Long Debate". NASA. 7 August 2017. Retrieved 5 May 2022.
  143. ^ Lewis, John S. (2004). Physics and Chemistry of the Solar System (2nd ed.). Academic Press. p. 425. ISBN 978-0-12-446744-6.
  144. ^ "Approximate Positions of the Planets". Solar System Dynamics. Jet Propulsion Laboratory. Retrieved 11 July 2022.
  145. ^ "Horizons System". Solar System Dynamics. Jet Propulsion Laboratory. Retrieved 12 July 2022.
  146. ^ a b "Planet Compare". Solar System Exploration. NASA. Retrieved 12 July 2022.
  147. ^ "Pre-generated Exoplanet Plots". NASA Exoplanet Archive. Retrieved 24 June 2022.
  148. ^ Schneider, J. "Interactive Extra-solar Planets Catalog". The Extrasolar Planets Encyclopedia. Retrieved 1 August 2023.
  149. ^ Cassan, Arnaud; Kubas, D.; Beaulieu, J.-P.; Dominik, M.; et al. (12 January 2012). "One or more bound planets per Milky Way star from microlensing observations". Nature. 481 (7380): 167–169. arXiv:1202.0903. Bibcode:2012Natur.481..167C. doi:10.1038/nature10684. PMID 22237108. S2CID 2614136.
  150. ^ Wolszczan, Alex (2008). "Planets Around the Pulsar PSR B1257+12". Extreme Solar Systems. 398: 3+. Bibcode:2008ASPC..398....3W. Retrieved 13 May 2022.
  151. ^ a b "What worlds are out there?". Canadian Broadcasting Corporation. 25 August 2016. Retrieved 5 June 2017.
  152. ^ Chen, Rick (23 October 2018). "Top Science Results from the Kepler Mission". NASA. Retrieved 11 July 2022. The most common size of planet Kepler found doesn't exist in our solar system—a world between the size of Earth and Neptune—and we have much to learn about these planets.
  153. ^ a b Barclay, Thomas; Rowe, Jason F.; Lissauer, Jack J.; Huber, Daniel; et al. (28 February 2013). "A sub-Mercury-sized exoplanet". Nature. 494 (7438): 452–454. arXiv:1305.5587. Bibcode:2013Natur.494..452B. doi:10.1038/nature11914. ISSN 0028-0836. PMID 23426260. S2CID 205232792.
  154. ^ Johnson, Michele (20 December 2011). "NASA Discovers First Earth-size Planets Beyond Our Solar System". NASA. Retrieved 20 December 2011.
  155. ^ Hand, Eric (20 December 2011). "Kepler discovers first Earth-sized exoplanets". Nature. doi:10.1038/nature.2011.9688. S2CID 122575277.
  156. ^ Overbye, Dennis (20 December 2011). "Two Earth-Size Planets Are Discovered". The New York Times. Retrieved 21 December 2011.
  157. ^ Kopparapu, Ravi Kumar (2013). "A revised estimate of the occurrence rate of terrestrial planets in the habitable zones around kepler m-dwarfs". The Astrophysical Journal Letters. 767 (1): L8. arXiv:1303.2649. Bibcode:2013ApJ...767L...8K. doi:10.1088/2041-8205/767/1/L8. S2CID 119103101.
  158. ^ Watson, Traci (10 May 2016). "NASA discovery doubles the number of known planets". USA Today. Retrieved 10 May 2016.
  159. ^ "The Habitable Exoplanets Catalog". Planetary Habitability Laboratory. University of Puerto Rico at Arecibo. Retrieved 12 July 2022.
  160. ^ Sanders, R. (4 November 2013). "Astronomers answer key question: How common are habitable planets?". Archived from the original on 7 November 2014. Retrieved 7 November 2013.
  161. ^ Petigura, E. A.; Howard, A. W.; Marcy, G. W. (2013). "Prevalence of Earth-size planets orbiting Sun-like stars". Proceedings of the National Academy of Sciences. 110 (48): 19273–19278. arXiv:1311.6806. Bibcode:2013PNAS..11019273P. doi:10.1073/pnas.1319909110. PMC 3845182. PMID 24191033.
  162. ^ Drake, Frank (29 September 2003). "The Drake Equation Revisited". Astrobiology Magazine. Archived from the original on 28 June 2011. Retrieved 23 August 2008.((cite news)): CS1 maint: unfit URL (link)
  163. ^ a b c Chen, Jingjing; Kipping, David (2016). "Probabilistic Forecasting of the Masses and Radii of Other Worlds". The Astrophysical Journal. 834 (1): 17. arXiv:1603.08614. doi:10.3847/1538-4357/834/1/17. S2CID 119114880. Retrieved 27 July 2021.
  164. ^ Mayor, Michel; Bonfils, Xavier; Forveille, Thierry; et al. (2009). "The HARPS search for southern extra-solar planets, XVIII. An Earth-mass planet in the GJ 581 planetary system" (PDF). Astronomy and Astrophysics. 507 (1): 487–494. arXiv:0906.2780. Bibcode:2009A&A...507..487M. doi:10.1051/0004-6361/200912172. S2CID 2983930. Archived from the original (PDF) on 21 May 2009.
  165. ^ "New 'super-Earth' found in space". BBC News. 25 April 2007. Retrieved 25 April 2007.
  166. ^ von Bloh; et al. (2007). "The Habitability of Super-Earths in Gliese 581". Astronomy and Astrophysics. 476 (3): 1365–1371. arXiv:0705.3758. Bibcode:2007A&A...476.1365V. doi:10.1051/0004-6361:20077939. S2CID 14475537.
  167. ^ Zhang, Zhoujian; Liu, Michael C.; Claytor, Zachary R.; Best, William M. J.; et al. (1 August 2021). "The Second Discovery from the COCONUTS Program: A Cold Wide-orbit Exoplanet around a Young Field M Dwarf at 10.9 pc". The Astrophysical Journal Letters. 916 (2): L11. arXiv:2107.02805. Bibcode:2021ApJ...916L..11Z. doi:10.3847/2041-8213/ac1123. hdl:20.500.11820/4f26e8e5-5d42-4259-bc20-fcb093d664b6. ISSN 2041-8205. S2CID 236464073.
  168. ^ "Extrasolar Planets". Retrieved 13 May 2022.
  169. ^ Anderson, D. R.; Hellier, C.; Gillon, M.; Triaud, A. H. M. J.; et al. (2009). "WASP-17b: an ultra-low density planet in a probable retrograde orbit". The Astrophysical Journal. 709 (1): 159–167. arXiv:0908.1553. Bibcode:2010ApJ...709..159A. doi:10.1088/0004-637X/709/1/159. S2CID 53628741.
  170. ^ a b c d e Young, Charles Augustus (1902). Manual of Astronomy: A Text Book. Ginn & company. pp. 324–327.
  171. ^ Dvorak, R.; Kurths, J.; Freistetter, F. (2005). Chaos And Stability in Planetary Systems. New York: Springer. p. 90. ISBN 978-3-540-28208-2.
  172. ^ Moorhead, Althea V.; Adams, Fred C. (2008). "Eccentricity evolution of giant planet orbits due to circumstellar disk torques". Icarus. 193 (2): 475–484. arXiv:0708.0335. Bibcode:2008Icar..193..475M. doi:10.1016/j.icarus.2007.07.009. S2CID 16457143.
  173. ^ "Planets – Kuiper Belt Objects". The Astrophysics Spectator. 15 December 2004. Archived from the original on 23 March 2021. Retrieved 23 August 2008.
  174. ^ Tatum, J. B. (2007). "17. Visual binary stars". Celestial Mechanics. Personal web page. Retrieved 2 February 2008.
  175. ^ Trujillo, Chadwick A.; Brown, Michael E. (2002). "A Correlation between Inclination and Color in the Classical Kuiper Belt". Astrophysical Journal. 566 (2): L125. arXiv:astro-ph/0201040. Bibcode:2002ApJ...566L.125T. doi:10.1086/339437. S2CID 11519263.
  176. ^ Peter Goldreich (November 1966). "History of the Lunar Orbit". Reviews of Geophysics. 4 (4): 411. Bibcode:1966RvGSP...4..411G. doi:10.1029/RG004i004p00411.
  177. ^ a b Harvey, Samantha (1 May 2006). "Weather, Weather, Everywhere?". NASA. Archived from the original on 31 August 2006. Retrieved 23 August 2008.
  178. ^ Planetary Fact Sheets, at
  179. ^ Schorghofer, N.; Mazarico, E.; Platz, T.; Preusker, F.; Schröder, S. E.; Raymond, C. A.; Russell, C. T. (6 July 2016). "The permanently shadowed regions of dwarf planet Ceres". Geophysical Research Letters. 43 (13): 6783–6789. Bibcode:2016GeoRL..43.6783S. doi:10.1002/2016GL069368.
  180. ^ Carry, B.; et al. (2009). "Physical properties of (2) Pallas". Icarus. 205 (2): 460–472. arXiv:0912.3626. Bibcode:2010Icar..205..460C. doi:10.1016/j.icarus.2009.08.007. S2CID 119194526.
  181. ^ Thomas, P. C.; et al. (1997). "Vesta: Spin Pole, Size, and Shape from HST Images". Icarus. 128 (1): 88–94. Bibcode:1997Icar..128...88T. doi:10.1006/icar.1997.5736.
  182. ^ Winn, Joshua N.; Holman, Matthew J. (2005). "Obliquity Tides on Hot Jupiters". The Astrophysical Journal. 628 (2): L159. arXiv:astro-ph/0506468. Bibcode:2005ApJ...628L.159W. doi:10.1086/432834. S2CID 7051928.
  183. ^ Seidelmann, P. Kenneth, ed. (1992). Explanatory Supplement to the Astronomical Almanac. University Science Books. p. 384.
  184. ^ Lang, Kenneth R. (2011). The Cambridge Guide to the Solar System (2nd ed.). Cambridge University Press. ISBN 978-1139494175. Archived from the original on 1 January 2016.
  185. ^ Bills, Bruce G. (2005). "Free and forced obliquities of the Galilean satellites of Jupiter". Icarus. 175 (1): 233–247. Bibcode:2005Icar..175..233B. doi:10.1016/j.icarus.2004.10.028.
  186. ^ Goldstein, R. M.; Carpenter, R. L. (1963). "Rotation of Venus: Period Estimated from Radar Measurements". Science. 139 (3558): 910–911. Bibcode:1963Sci...139..910G. doi:10.1126/science.139.3558.910. PMID 17743054. S2CID 21133097.
  187. ^ a b Belton, M. J. S.; Terrile, R. J. (1984). Bergstralh, J. T. (ed.). Rotational properties of Uranus and Neptune. Voyager "Uranus-Neptune" Workshop Pasadena February 6–8, 1984. pp. 327–347. Bibcode:1984NASCP2330..327B.
  188. ^ Borgia, Michael P. (2006). The Outer Worlds; Uranus, Neptune, Pluto, and Beyond. Springer New York. pp. 195–206.
  189. ^ Lissauer, Jack J. (September 1993). "Planet formation". Annual Review of Astronomy and Astrophysics. 31: 129–174. Bibcode:1993ARA&A..31..129L. doi:10.1146/annurev.aa.31.090193.001021.
  190. ^ Zarka, Philippe; Treumann, Rudolf A.; Ryabov, Boris P.; Ryabov, Vladimir B. (2001). "Magnetically-Driven Planetary Radio Emissions and Application to Extrasolar Planets". Astrophysics and Space Science. 277 (1/2): 293–300. Bibcode:2001Ap&SS.277..293Z. doi:10.1023/A:1012221527425. S2CID 16842429.
  191. ^ Liu, Han-Shou; O'Keefe, John A. (1965). "Theory of Rotation for the Planet Mercury". Science. 150 (3704): 1717. Bibcode:1965Sci...150.1717L. doi:10.1126/science.150.3704.1717. PMID 17768871. S2CID 45608770.
  192. ^ Correia, Alexandre C. M.; Laskar, Jacques; De Surgy, Olivier Néron (May 2003). "Long-Term Evolution of the Spin of Venus, Part I: Theory" (PDF). Icarus. 163 (1): 1–23. Bibcode:2003Icar..163....1C. doi:10.1016/S0019-1035(03)00042-3. Archived (PDF) from the original on 27 September 2019. Retrieved 9 September 2006.
  193. ^ Laskar, Jacques; De Surgy, Olivier Néron (2003). "Long-Term Evolution of the Spin of Venus, Part II: Numerical Simulations" (PDF). Icarus. 163 (1): 24–45. Bibcode:2003Icar..163...24C. doi:10.1016/S0019-1035(03)00043-5. Archived (PDF) from the original on 2 May 2019. Retrieved 9 September 2006.
  194. ^ Schutz, Bernard (2003). Gravity from the Ground Up. Cambridge University Press. p. 43. ISBN 978-0521455060. Retrieved 24 April 2017.
  195. ^ Young, Leslie A. (1997). "The Once and Future Pluto". Southwest Research Institute, Boulder, Colorado. Retrieved 26 March 2007.
  196. ^ Szakáts, R.; Kiss, Cs.; Ortiz, J. L.; Morales, N.; Pál, A.; Müller, T. G.; et al. (2023). "Tidally locked rotation of the dwarf planet (136199) Eris discovered via long-term ground-based and space photometry". Astronomy & Astrophysics. 669: L3. arXiv:2211.07987. Bibcode:2023A&A...669L...3S. doi:10.1051/0004-6361/202245234. S2CID 253522934.
  197. ^ Ortiz, J. L.; Cikota, A.; Cikota, S.; Hestroffer, D.; Thirouin, A.; Morales, N.; Duffard, R.; Gil-Hutton, R.; Santos-Sanz, P.; De La Cueva, I. (2010). "A mid-term astrometric and photometric study of trans-Neptunian object (90482) Orcus". Astronomy & Astrophysics. 525: A31. arXiv:1010.6187. Bibcode:2011A&A...525A..31O. doi:10.1051/0004-6361/201015309. S2CID 56051949.
  198. ^ Rabinowitz, D. L.; Barkume, Kristina; Brown, Michael E.; Roe, Henry; Schwartz, Michael; Tourtellotte, Suzanne; Trujillo, Chad (2006). "Photometric Observations Constraining the Size, Shape, and Albedo of 2003 EL61, a Rapidly Rotating, Pluto-Sized Object in the Kuiper Belt". Astrophysical Journal. 639 (2): 1238–1251. arXiv:astro-ph/0509401. Bibcode:2006ApJ...639.1238R. doi:10.1086/499575. S2CID 11484750.
  199. ^ Singal, Ashok K. (May 2014). "Life on a tidally-locked planet". Planex Newsletter. 4 (2): 8. arXiv:1405.1025. Bibcode:2014arXiv1405.1025S.
  200. ^ Walker, G. A. H.; et al. (2008). "MOST detects variability on tau Bootis possibly induced by its planetary companion". Astronomy and Astrophysics. 482 (2): 691–697. arXiv:0802.2732. Bibcode:2008A&A...482..691W. doi:10.1051/0004-6361:20078952. S2CID 56317105.
  201. ^ Faber, Peter; Quillen, Alice C. (26 November 2007). "The Total Number of Giant Planets in Debris Disks with Central Clearings". Monthly Notices of the Royal Astronomical Society. 382 (4): 1823–1828. arXiv:0706.1684. Bibcode:2007MNRAS.382.1823F. doi:10.1111/j.1365-2966.2007.12490.x. S2CID 16610947.
  202. ^ Milbert, D. G.; Smith, D. A. "Converting GPS Height into NAVD88 Elevation with the GEOID96 Geoid Height Model". National Geodetic Survey, NOAA. Retrieved 7 March 2007.
  203. ^ Sandwell, D. T.; Smith, Walter H. F. (7 July 2006). "Exploring the Ocean Basins with Satellite Altimeter Data". NOAA/NGDC. Archived from the original on 15 July 2014. Retrieved 21 April 2007.
  204. ^ Wieczorek, M. A. (2015), Schubert, Gerald (ed.), "10.05 – Gravity and Topography of the Terrestrial Planets", Treatise on Geophysics (2nd ed.), Oxford: Elsevier, pp. 153–193, ISBN 978-0-444-53803-1, retrieved 13 May 2022
  205. ^ Brown, Michael E. (2006). "The Dwarf Planets". California Institute of Technology. Retrieved 1 February 2008.
  206. ^ Schneider, J. (2016). "III.8 Exoplanets versus brown dwarfs: The CoRoT view and the future". The CoRoT Legacy Book. EDP Sciences. p. 157. arXiv:1604.00917. doi:10.1051/978-2-7598-1876-1.c038. ISBN 978-2-7598-1876-1. S2CID 118434022.
  207. ^ Wright, Jason T; Fakhouri, Onsi; Marcy, G.; Han, Eunkyu; et al. (2010). "The Exoplanet Orbit Database". Publications of the Astronomical Society of the Pacific. 123 (902): 412–422. arXiv:1012.5676. Bibcode:2011PASP..123..412W. doi:10.1086/659427. S2CID 51769219.
  208. ^ Konacki, M.; Wolszczan, A. (2003). "Masses and Orbital Inclinations of Planets in the PSR B1257+12 System". The Astrophysical Journal. 591 (2): L147–L150. arXiv:astro-ph/0305536. Bibcode:2003ApJ...591L.147K. doi:10.1086/377093. S2CID 18649212.
  209. ^ Veras, Dimitri (2021). "Planetary Systems Around White Dwarfs". Oxford Research Encyclopedia of Planetary Science. Oxford University Press. arXiv:2106.06550. doi:10.1093/acrefore/9780190647926.013.238. ISBN 978-0-19-064792-6. Retrieved 12 July 2022.
  210. ^ a b Jacobson, Robert. A. (1 November 2022). "The Orbits of the Main Saturnian Satellites, the Saturnian System Gravity Field, and the Orientation of Saturn's Pole*". The Astronomical Journal. 164 (5): 199. Bibcode:2022AJ....164..199J. doi:10.3847/1538-3881/ac90c9. S2CID 252992162.
  211. ^ Thomas, P. C. (July 2010). "Sizes, shapes, and derived properties of the saturnian satellites after the Cassini nominal mission" (PDF). Icarus. 208 (1): 395–401. Bibcode:2010Icar..208..395T. doi:10.1016/j.icarus.2010.01.025. Archived from the original (PDF) on 23 December 2018. Retrieved 7 May 2023.
  212. ^ Jia-Rui C. Cook and Dwayne Brown (26 April 2012). "Cassini Finds Saturn Moon Has Planet-Like Qualities". JPL/NASA. Archived from the original on 27 April 2012.
  213. ^ Gaffey, Michael (1984). "Rotational spectral variations of asteroid (8) Flora: Implications for the nature of the S-type asteroids and for the parent bodies of the ordinary chondrites". Icarus. 60 (1): 83–114. Bibcode:1984Icar...60...83G. doi:10.1016/0019-1035(84)90140-4.
  214. ^ Hardersen, Paul S.; Gaffey, Michael J. & Abell, Paul A. (2005). "Near-IR spectral evidence for the presence of iron-poor orthopyroxenes on the surfaces of six M-type asteroid". Icarus. 175 (1): 141. Bibcode:2005Icar..175..141H. doi:10.1016/j.icarus.2004.10.017.
  215. ^ a b Asphaug, E.; Reufer, A. (2014). "Mercury and other iron-rich planetary bodies as relics of inefficient accretion". Nature Geoscience. 7 (8): 564–568. Bibcode:2014NatGe...7..564A. doi:10.1038/NGEO2189.
  216. ^ a b "Planetary Interiors". Department of Physics, University of Oregon. Archived from the original on 8 August 2012. Retrieved 23 August 2008.
  217. ^ Elkins-Tanton, Linda T. (2006). Jupiter and Saturn. New York: Chelsea House. ISBN 978-0-8160-5196-0.
  218. ^ Podolak, M.; Weizman, A.; Marley, M. (December 1995). "Comparative models of Uranus and Neptune". Planetary and Space Science. 43 (12): 1517–1522. Bibcode:1995P&SS...43.1517P. doi:10.1016/0032-0633(95)00061-5.
  219. ^ Neumann, W.; Breuer, D.; Spohn, T. (2 December 2015). "Modelling the internal structure of Ceres: Coupling of accretion with compaction by creep and implications for the water-rock differentiation" (PDF). Astronomy & Astrophysics. 584: A117. Bibcode:2015A&A...584A.117N. doi:10.1051/0004-6361/201527083. Archived (PDF) from the original on 22 August 2016. Retrieved 10 July 2016.
  220. ^ Monteux, J.; Tobie, G.; Choblet, G.; Le Feuvre, M. (2014). "Can large icy moons accrete undifferentiated?" (PDF). Icarus. 237: 377–387. Bibcode:2014Icar..237..377M. doi:10.1016/j.icarus.2014.04.041. S2CID 46172826.
  221. ^ "A look into Vesta's interior". Max-Planck-Gesellschaft. 6 January 2011.
  222. ^ Zurbuchen TH, Raines JM, Gloeckler G, Krimigis SM, et al. (2008). "MESSENGER Observations of the Composition of Mercury's Ionized Exosphere and Plasma Environment". Science. 321 (5885): 90–92. Bibcode:2008Sci...321...90Z. doi:10.1126/science.1159314. PMID 18599777. S2CID 206513512.
  223. ^ Coustenis, Athéna & Taylor, F. W. (2008). Titan: Exploring an Earthlike World. World Scientific. p. 130. ISBN 978-981-270-501-3. Retrieved 25 March 2010.
  224. ^ "Neptune: Moons: Triton". Solar System Exploration. Archived from the original on 10 January 2008. Retrieved 31 December 2007.
  225. ^ Lellouch, E.; de Bergh, C.; Sicardy, B.; Forget, F.; Vangvichith, M.; Käufl, H.-U. (January 2015). "Exploring the spatial, temporal, and vertical distribution of methane in Pluto's atmosphere". Icarus. 246: 268–278. arXiv:1403.3208. Bibcode:2015Icar..246..268L. doi:10.1016/j.icarus.2014.03.027. S2CID 119194193.
  226. ^ Sheppard, S. S.; Jewitt, D.; Kleyna, J. (2005). "An Ultradeep Survey for Irregular Satellites of Uranus: Limits to Completeness". The Astronomical Journal. 129 (1): 518–525. arXiv:astro-ph/0410059. Bibcode:2005AJ....129..518S. doi:10.1086/426329. S2CID 18688556.
  227. ^ Zeilik, Michael A.; Gregory, Stephan A. (1998). Introductory Astronomy & Astrophysics (4th ed.). Saunders College Publishing. p. 67. ISBN 978-0-03-006228-5.
  228. ^ Haberle, R. M. (2015), "Solar System/Sun, Atmospheres, Evolution of Atmospheres | Planetary Atmospheres: Mars", in North, Gerald R.; Pyle, John; Zhang, Fuqing (eds.), Encyclopedia of Atmospheric Sciences (2nd ed.), Academic Press, pp. 168–177, doi:10.1016/b978-0-12-382225-3.00312-1, ISBN 978-0123822253
  229. ^ Basilevsky, Alexandr T.; Head, James W. (2003). "The surface of Venus". Rep. Prog. Phys. 66 (10): 1699–1734. Bibcode:2003RPPh...66.1699B. doi:10.1088/0034-4885/66/10/R04. S2CID 250815558.
  230. ^ S. I. Rasoonl & C. de Bergh (1970). "The Runaway Greenhouse Effect and the Accumulation of CO2 in the Atmosphere of Venus". Nature. 226 (5250): 1037–1039. Bibcode:1970Natur.226.1037R. doi:10.1038/2261037a0. PMID 16057644. S2CID 4201521.
  231. ^ Badescu, Viorel (2015). Zacny, Kris (ed.). Inner Solar System: Prospective Energy and Material Resources. Heidelberg: Springer-Verlag GmbH. p. 492. ISBN 978-3319195681..
  232. ^ Horst, Sarah (2017). "Titan's Atmosphere and Climate". J. Geophys. Res. Planets. 122 (3): 432–482. arXiv:1702.08611. Bibcode:2017JGRE..122..432H. doi:10.1002/2016JE005240. S2CID 119482985.
  233. ^ Knutson, Heather A.; Charbonneau, David; Allen, Lori E.; Fortney, Jonathan J. (2007). "A map of the day-night contrast of the extrasolar planet HD 189733 b". Nature. 447 (7141): 183–186. arXiv:0705.0993. Bibcode:2007Natur.447..183K. doi:10.1038/nature05782. PMID 17495920. S2CID 4402268.
  234. ^ Demory, Brice-Olivier; de Wit, Julien; Lewis, Nikole; Fortney, Jonathan; et al. (2013). "Inference of Inhomogeneous Clouds in an Exoplanet Atmosphere". The Astrophysical Journal Letters. 776 (2): L25. arXiv:1309.7894. Bibcode:2013ApJ...776L..25D. doi:10.1088/2041-8205/776/2/L25. S2CID 701011.
  235. ^ Moses, Julianne (1 January 2014). "Extrasolar planets: Cloudy with a chance of dustballs". Nature. 505 (7481): 31–32. Bibcode:2014Natur.505...31M. doi:10.1038/505031a. PMID 24380949. S2CID 4408861.
  236. ^ Benneke, Björn; Wong, Ian; Piaulet, Caroline; Knutson, Heather A.; et al. (10 December 2019). "Water Vapor and Clouds on the Habitable-zone Sub-Neptune Exoplanet K2-18b". The Astrophysical Journal Letters. 887 (1): L14. arXiv:1909.04642. Bibcode:2019ApJ...887L..14B. doi:10.3847/2041-8213/ab59dc. ISSN 2041-8205. S2CID 209324670.
  237. ^ Ballester, Gilda E.; Sing, David K.; Herbert, Floyd (2007). "The signature of hot hydrogen in the atmosphere of the extrasolar planet HD 209458b" (PDF). Nature. 445 (7127): 511–514. Bibcode:2007Natur.445..511B. doi:10.1038/nature05525. hdl:10871/16060. PMID 17268463. S2CID 4391861.
  238. ^ Villarreal D'Angelo, Carolina; Esquivel, Alejandro; Schneiter, Matías; Sgró, Mario Agustín (21 September 2018). "Magnetized winds and their influence in the escaping upper atmosphere of HD 209458b". Monthly Notices of the Royal Astronomical Society. 479 (3): 3115–3125. doi:10.1093/mnras/sty1544. hdl:11336/86936. ISSN 0035-8711.
  239. ^ Harrington, Jason; Hansen, Brad M.; Luszcz, Statia H.; Seager, Sara (2006). "The phase-dependent infrared brightness of the extrasolar planet Andromeda b". Science. 314 (5799): 623–626. arXiv:astro-ph/0610491. Bibcode:2006Sci...314..623H. doi:10.1126/science.1133904. PMID 17038587. S2CID 20549014.
  240. ^ Showman, Adam P.; Tan, Xianyu; Parmentier, Vivien (December 2020). "Atmospheric Dynamics of Hot Giant Planets and Brown Dwarfs". Space Science Reviews. 216 (8): 139. arXiv:2007.15363. Bibcode:2020SSRv..216..139S. doi:10.1007/s11214-020-00758-8. ISSN 0038-6308. S2CID 220870881.
  241. ^ Fortney, Jonathan J.; Dawson, Rebekah I.; Komacek, Thaddeus D. (March 2021). "Hot Jupiters: Origins, Structure, Atmospheres". Journal of Geophysical Research: Planets. 126 (3). arXiv:2102.05064. Bibcode:2021JGRE..12606629F. doi:10.1029/2020JE006629. ISSN 2169-9097. S2CID 231861632.
  242. ^ a b c Kivelson, Margaret Galland; Bagenal, Fran (2007). "Planetary Magnetospheres". In Lucy-Ann McFadden; Paul Weissman; Torrence Johnson (eds.). Encyclopedia of the Solar System. Academic Press. p. 519. ISBN 978-0-12-088589-3.
  243. ^ De Angelis, G.; Clowdsley, M. S.; Nealy, J. E.; Tripathi, R. K.; et al. (January 2004). "Radiation analysis for manned missions to the Jupiter system". Advances in Space Research. 34 (6): 1395–1403. Bibcode:2004AdSpR..34.1395D. doi:10.1016/j.asr.2003.09.061. PMID 15881781.
  244. ^ Gefter, Amanda (17 January 2004). "Magnetic planet". Astronomy. Retrieved 29 January 2008.
  245. ^ Shkolnik, E.; Walker, G. A. H.; Bohlender, D. A. (10 November 2003). "Evidence for Planet-induced Chromospheric Activity on HD 179949". The Astrophysical Journal. 597 (2): 1092–1096. Bibcode:2003ApJ...597.1092S. doi:10.1086/378583. ISSN 0004-637X. S2CID 15829056.
  246. ^ Grasset, O.; Sotin, C.; Deschamps, F. (2000). "On the internal structure and dynamic of Titan". Planetary and Space Science. 48 (7–8): 617–636. Bibcode:2000P&SS...48..617G. doi:10.1016/S0032-0633(00)00039-8.
  247. ^ Fortes, A. D. (2000). "Exobiological implications of a possible ammonia-water ocean inside Titan". Icarus. 146 (2): 444–452. Bibcode:2000Icar..146..444F. doi:10.1006/icar.2000.6400.
  248. ^ Jones, Nicola (11 December 2001). "Bacterial explanation for Europa's rosy glow". New Scientist Print Edition. Archived from the original on 10 April 2008. Retrieved 23 August 2008.
  249. ^ Taubner, Ruth-Sophie; Pappenreiter, Patricia; Zwicker, Jennifer; Smrzka, Daniel; Pruckner, Christian; Kolar, Philipp; Bernacchi, Sébastien; Seifert, Arne H.; Krajete, Alexander; Bach, Wolfgang; Peckmann, Jörn; Paulik, Christian; Firneis, Maria G.; Schleper, Christa; Rittmann, Simon K.-M. R. (27 February 2018). "Biological methane production under putative Enceladus-like conditions". Nature Communications. 9 (1): 748. Bibcode:2018NatCo...9..748T. doi:10.1038/s41467-018-02876-y. ISSN 2041-1723. PMC 5829080. PMID 29487311.
  250. ^ Affholder, Antonin; et al. (7 June 2021). "Bayesian analysis of Enceladus's plume data to assess methanogenesis". Nature Astronomy. 5 (8): 805–814. Bibcode:2021NatAs...5..805A. doi:10.1038/s41550-021-01372-6. S2CID 236220377. Archived from the original on 7 July 2021. Retrieved 7 July 2021.
  251. ^ Molnar, L. A.; Dunn, D. E. (1996). "On the Formation of Planetary Rings". Bulletin of the American Astronomical Society. 28: 77–115. Bibcode:1996DPS....28.1815M.
  252. ^ Thérèse, Encrenaz (2004). The Solar System (3rd ed.). Springer. pp. 388–390. ISBN 978-3-540-00241-3.
  253. ^ Ortiz, J. L.; Santos-Sanz, P.; Sicardy, B.; Benedetti-Rossi, G.; Bérard, D.; Morales, N.; et al. (2017). "The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation" (PDF). Nature. 550 (7675): 219–223. arXiv:2006.03113. Bibcode:2017Natur.550..219O. doi:10.1038/nature24051. hdl:10045/70230. PMID 29022593. S2CID 205260767.
  254. ^ B. E. Morgado; et al. (8 February 2023). "A dense ring of the trans-Neptunian object Quaoar outside its Roche limit". Nature. 614 (7947): 239–243. doi:10.1038/S41586-022-05629-6. ISSN 1476-4687. Wikidata Q116754015.
  255. ^ Luhman, K. L.; Adame, Lucía; D'Alessio, Paola; Calvet, Nuria (2005). "Discovery of a Planetary-Mass Brown Dwarf with a Circumstellar Disk". Astrophysical Journal. 635 (1): L93. arXiv:astro-ph/0511807. Bibcode:2005ApJ...635L..93L. doi:10.1086/498868. S2CID 11685964.
  256. ^ Joergens, V.; Bonnefoy, M.; Liu, Y.; Bayo, A.; et al. (2013). "OTS 44: Disk and accretion at the planetary border". Astronomy & Astrophysics. 558 (7): L7. arXiv:1310.1936. Bibcode:2013A&A...558L...7J. doi:10.1051/0004-6361/201322432. S2CID 118456052.