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77-484: Planetary geology includes such topics as determining the properties and processes of the internal structure of the terrestrial planets , and also looks at planetary volcanism and surface processes such as impact craters , fluvial and aeolian processes . The structures and compositions of the giant planets and their moons are also examined, as is the make-up of the minor bodies of the Solar System, such as asteroids,

154-605: A mean diameter of 2,377 ± 4 kilometres (1,477 ± 2 mi) in July 2015. Eris was discovered by the team of Mike Brown , Chad Trujillo , and David Rabinowitz on January 5, 2005, from images taken on October 21, 2003. The discovery was announced on July 29, 2005, the same day as Makemake and two days after Haumea , due in part to events that would later lead to controversy about Haumea . The search team had been systematically scanning for large outer Solar System bodies for several years, and had been involved in

231-450: A "long" or with a "short" e , analogous to the two competing pronunciations of the word era . Perhaps the more common form in English, used i.a. by Brown and his students, is / ˈ ɛr ɪ s / with disyllabic laxing and a short e . However, the classical English pronunciation of the goddess is / ˈ ɪər ɪ s / , with a long e . The Greek and Latin oblique stem of the name

308-547: A different team in Spain. Precovery images of Eris have been identified back to September 3, 1954. More observations released in October 2005 revealed that Eris has a moon, later named Dysnomia . Observations of Dysnomia's orbit permitted scientists to determine the mass of Eris, which in June 2007 was calculated to be (1.66 ± 0.02) × 10  kg , 27% ± 2% greater than Pluto's. Eris

385-473: A little smaller than Pluto by area and diameter, which is 2372 ± 4 km across, although Eris is more massive. It also indicates a geometric albedo of 0.96. It is speculated that the high albedo is due to the surface ices being replenished because of temperature fluctuations as Eris's eccentric orbit takes it closer and farther from the Sun. The mass of Eris can be calculated with much greater precision. Based on

462-409: A model of the planet's structure. Where there have been landers or multiple orbiting spacecraft, these models are constrained by seismological data and also moment of inertia data derived from the spacecraft's orbits. Where such data is not available, uncertainties are inevitably higher. The uncompressed densities of the rounded terrestrial bodies directly orbiting the Sun trend towards lower values as

539-671: A museum of planetary geology. The Geological Society of America's Planetary Geology Division has been growing and thriving since May 1981 and has two mottos: "One planet just isn't enough!" and "The GSA Division with the biggest field area!" Major centers for planetary science research include the Lunar and Planetary Institute , Applied Physics Laboratory , Planetary Science Institute , Jet Propulsion Laboratory , Southwest Research Institute , and Johnson Space Center . Additionally, several universities conduct extensive planetary science research, including Montana State University , Brown University ,

616-538: A period of time, the object became known to the wider public as Xena . "Xena" was an informal name used internally by the discovery team, inspired by the title character of the television series Xena: Warrior Princess . The discovery team had reportedly saved the nickname "Xena" for the first body they discovered that was larger than Pluto. According to Brown, We chose it since it started with an X ( planet "X" ), it sounds mythological ... and we've been working to get more female deities out there ( e.g. Sedna ). Also, at

693-646: A possibly unique identifying name. The conventions which decide the more precise name are dependent on which planetary body the feature is on, but the standard descriptors are in general common to all astronomical planetary bodies. Some names have a long history of historical usage, but new must be recognized by the IAU Working Group for Planetary System Nomenclature as features are mapped and described by new planetary missions. This means that in some cases, names may change as new imagery becomes available, or in other cases widely adopted informal names changed in line with

770-407: A preliminary determination of Eris's orbit , which allowed the object's distance to be estimated. The team had planned to delay announcing their discoveries of the bright objects Eris and Makemake until further observations and calculations were complete, but announced them both on July 29 when the discovery of another large TNO they had been tracking—Haumea—was controversially announced on July 27 by

847-478: A similar density but has a significant ice layer on the surface: for this reason, it is sometimes considered an icy planet instead. Terrestrial planets can have surface structures such as canyons , craters , mountains , volcanoes , and others, depending on the presence at any time of an erosive liquid or tectonic activity or both. Terrestrial planets have secondary atmospheres , generated by volcanic out-gassing or from comet impact debris. This contrasts with

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924-400: A similar structure; possibly so does the smaller one 21 Lutetia . Another rocky asteroid 2 Pallas is about the same size as Vesta, but is significantly less dense; it appears to have never differentiated a core and a mantle. The Earth's Moon and Jupiter's moon Io have similar structures to terrestrial planets, but Earth's Moon has a much smaller iron core. Another Jovian moon Europa has

1001-479: A solid planetary surface , making them substantially different from larger gaseous planets , which are composed mostly of some combination of hydrogen , helium , and water existing in various physical states . All terrestrial planets in the Solar System have the same basic structure, such as a central metallic core (mostly iron ) with a surrounding silicate mantle . The large rocky asteroid 4 Vesta has

1078-607: A solid surface, but are composed of ice and rock rather than of rock and metal. These include the dwarf planets, such as Ceres , Pluto and Eris , which are found today only in the regions beyond the formation snow line where water ice was stable under direct sunlight in the early Solar System. It also includes the other round moons, which are ice-rock (e.g. Ganymede , Callisto , Titan , and Triton ) or even almost pure (at least 99%) ice ( Tethys and Iapetus ). Some of these bodies are known to have subsurface hydrospheres (Ganymede, Callisto, Enceladus , and Titan), like Europa, and it

1155-497: A terrestrial planet is the average density its materials would have at zero pressure . A greater uncompressed density indicates a greater metal content. Uncompressed density differs from the true average density (also often called "bulk" density) because compression within planet cores increases their density; the average density depends on planet size, temperature distribution, and material stiffness as well as composition. Calculations to estimate uncompressed density inherently require

1232-533: Is Erid- , as can be seen in Italian Eride and Russian Эрида Erida , so the adjective in English is Eridian / ɛ ˈ r ɪ d i ə n / . Due to uncertainty over whether the object would be classified as a planet or a minor planet , because varying nomenclature procedures apply to these classes of objects, the decision on what to name the object had to wait until after the August 24, 2006, IAU ruling. For

1309-499: Is a trans-Neptunian dwarf planet. Its orbital characteristics more specifically categorize it as a scattered-disk object (SDO), or a TNO that has been "scattered" from the Kuiper belt into more-distant and unusual orbits following gravitational interactions with Neptune as the Solar System was forming. Although its high orbital inclination is unusual among the known SDOs, theoretical models suggest that objects that were originally near

1386-581: Is also possible for some others (e.g. Ceres, Mimas , Dione , Miranda , Ariel , Triton, and Pluto). Titan even has surface bodies of liquid, albeit liquid methane rather than water. Jupiter's Ganymede, though icy, does have a metallic core like the Moon, Io, Europa, and the terrestrial planets. The name Terran world has been suggested to define all solid worlds (bodies assuming a rounded shape), without regard to their composition. It would thus include both terrestrial and icy planets. The uncompressed density of

1463-475: Is also tidally locked to Eris, which makes the Eris–Dysnomia system the second known case of double-synchronous rotation, after Pluto and Charon . Previous measurements of Eris's rotation period obtained highly uncertain values ranging tens of hours to several days due to insufficient long-term coverage of Eris's rotation. The axial tilt of Eris has not been measured, but it can be reasonably assumed that it

1540-521: Is discouraged in astronomy, but NASA has used the Hand of Eris , ⟨ [REDACTED] ⟩ (U+2BF0), for Eris. This is a symbol from Discordianism , a religion concerned with the goddess Eris. Most astrologers use this symbol, while some use a symbol resembling that of Mars but with the arrow pointing downward, ⟨ [REDACTED] ⟩ (U+2BF1). Both symbols have been included in Unicode . Eris

1617-621: Is named after the Greek goddess Eris (Greek Ἔρις ), a personification of strife and discord. The name was proposed by the Caltech team on September 6, 2006, and it was assigned on September 13, 2006, following an unusually long period in which the object was known by the provisional designation 2003 UB 313 , which was granted automatically by the IAU under their naming protocols for minor planets . The name Eris has two competing pronunciations, with

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1694-506: Is not primordial and instead may have been produced from subsurface geochemical processes. Substantial quantities of nitrogen ice on Eris was also detected by the JWST, and it is presumed to have originated from subsurface processes similar to Eris's likely non-primordial methane. The abundance of nitrogen ice on Eris is estimated to be one-third of that of methane by volume. Unlike the somewhat reddish and variegated surfaces of Pluto and Triton,

1771-501: Is now understood to be the tenth-largest known object to directly orbit the Sun by volume, but remains the ninth-largest by mass. The discovery team followed up their initial identification of Eris with spectroscopic observations made at the 8 m Gemini North Telescope in Hawaii on January 25, 2005. Infrared light from the object revealed the presence of methane ice, indicating that the surface may be similar to that of Pluto, which at

1848-415: Is slightly larger by volume. Both Eris and Pluto have a surface area that is comparable to that of Russia or South America . Eris has one large known moon , Dysnomia . In February 2016, Eris's distance from the Sun was 96.3 AU (14.41 billion km; 8.95 billion mi), more than three times that of Neptune or Pluto. With the exception of long-period comets , Eris and Dysnomia were

1925-528: Is the ninth-most massive known object orbiting the Sun and the sixteenth-most massive overall in the Solar System (counting moons ). It is also the largest known object in the solar system that has not been visited by a spacecraft . Eris has been measured at 2,326 ± 12 kilometres (1,445 ± 7 mi) in diameter; its mass is 0.28% that of the Earth and 27% greater than that of Pluto , although Pluto

2002-556: Is the most massive and second-largest known dwarf planet in the Solar System . It is a trans-Neptunian object (TNO) in the scattered disk and has a high- eccentricity orbit. Eris was discovered in January 2005 by a Palomar Observatory –based team led by Mike Brown and verified later that year. It was named in September 2006 after the Greco–Roman goddess of strife and discord . Eris

2079-494: Is the same as Dysnomia's orbital inclination, which would be about 78 degrees with respect to the ecliptic. If this were the case, most of Eris's northern hemisphere would be illuminated by sunlight, with 30% of the hemisphere experiencing constant illumination in 2018. In 2005, the adaptive optics team at the Keck telescopes in Hawaii carried out observations of the four brightest TNOs (Pluto, Makemake, Haumea, and Eris), using

2156-733: Is unknown whether extrasolar terrestrial planets in general will follow such a trend. The data in the tables below are mostly taken from a list of gravitationally rounded objects of the Solar System and planetary-mass moon . All distances from the Sun are averages. Most of the planets discovered outside the Solar System are giant planets, because they are more easily detectable. But since 2005, hundreds of potentially terrestrial extrasolar planets have also been found, with several being confirmed as terrestrial. Most of these are super-Earths , i.e. planets with masses between Earth's and Neptune's; super-Earths may be gas planets or terrestrial, depending on their mass and other parameters. During

2233-612: The Astrogeology Research Program , within the United States Geological Survey . He made important contributions to the field and the study of impact craters , selenography (study of the Moon), asteroids, and comets. Today, many institutions are concerned with the study and communication of planetary sciences and planetary geology. The Visitor Center at Barringer Meteor Crater near Winslow, Arizona includes

2310-724: The Hubble Space Telescope ). The maps and images are stored in the NASA Planetary Data System where tools such as the Planetary Image Atlas help to search for certain items such as geological features including mountains, ravines, and craters. Planetary geology uses a wide variety of standardized descriptor names for features. All planetary feature names recognized by the International Astronomical Union (IAU) combine one of these names with

2387-415: The Kuiper belt , and comets. Planetary geology largely applies concepts within the geosciences to planetary bodies in the broadest sense, and includes applications derived from fields in the geological sciences, such as geophysics and geochemistry . Eugene Merle Shoemaker is credited with bringing geologic principles to planetary mapping and creating the branch of planetary science in the early 1960s,

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2464-675: The Milky Way galaxy . The following exoplanets have a density of at least 5 g/cm and a mass below Neptune's and are thus very likely terrestrial: Kepler-10b , Kepler-20b , Kepler-36b , Kepler-48d , Kepler 68c , Kepler-78b , Kepler-89b , Kepler-93b , Kepler-97b , Kepler-99b , Kepler-100b , Kepler-101c , Kepler-102b , Kepler-102d , Kepler-113b , Kepler-131b , Kepler-131c , Kepler-138c , Kepler-406b , Kepler-406c , Kepler-409b . In 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth- and super-Earth-sized planets orbiting in

2541-538: The Sun ( aphelion ) is 97.5  AU , and its closest ( perihelion ) is 38 AU. As the time of perihelion is defined at the epoch chosen using an unperturbed two-body solution , the further the epoch is from the date of perihelion, the less accurate the result. Numerical integration is required to predict the time of perihelion accurately. Numerical integration by JPL Horizons shows that Eris came to perihelion around 1699, to aphelion around 1977, and will return to perihelion around December 2257. Unlike those of

2618-1009: The University of Arizona , California Institute of Technology , University of Colorado , Western Michigan University , Massachusetts Institute of Technology , and Washington University in St. Louis . Planetary geologists usually study either geology , astronomy , planetary science , geophysics , or one of the earth sciences at the graduate level. Simulated interplanetary missions performed on Earth have studied procedures and tools for planetary geology. Various tools, including common archaeological tools such as hammers, shovels, brushes, were evaluated for use by planetary geologists. Along with these common tools, new advanced technologies have become available. These include spectroscopic databases, and data (such as mission logs, images and mapping) from previous unmanned interplanetary missions. Scientists use maps, images, telescopes on Earth, and orbiting telescopes (such as

2695-607: The habitable zones of Sun-like stars and red dwarfs within the Milky Way . Eleven billion of these estimated planets may be orbiting Sun-like stars. The nearest such planet may be 12 light-years away, according to the scientists. However, this does not give estimates for the number of extrasolar terrestrial planets, because there are planets as small as Earth that have been shown to be gas planets (see Kepler-138d ). Estimates show that about 80% of potentially habitable worlds are covered by land, and about 20% are ocean planets. Planets with rations more like those of Earth, which

2772-679: The inner planets closest to the Sun : Mercury , Venus , Earth and Mars . Among astronomers who use the geophysical definition of a planet , two or three planetary-mass satellites – Earth's Moon , Io , and sometimes Europa – may also be considered terrestrial planets. The large rocky asteroids Pallas and Vesta are sometimes included as well, albeit rarely. The terms "terrestrial planet" and "telluric planet" are derived from Latin words for Earth ( Terra and Tellus ), as these planets are, in terms of structure, Earth-like . Terrestrial planets are generally studied by geologists , astronomers , and geophysicists . Terrestrial planets have

2849-458: The northern sky , entering Perseus in 2128 and Camelopardalis (where it will reach its northernmost declination ) in 2173. In November 2010, Eris was the subject of one of the most distant stellar occultations yet from Earth. Preliminary data from this event cast doubt on previous size estimates. The teams announced their final results from the occultation in October 2011, with an estimated diameter of 2326 ± 12 km . This makes Eris

2926-484: The outer , giant planets , whose atmospheres are primary; primary atmospheres were captured directly from the original solar nebula . The Solar System has four terrestrial planets under the dynamical definition: Mercury , Venus , Earth and Mars . The Earth's Moon as well as Jupiter's moons Io and Europa would also count geophysically, as well as perhaps the large protoplanet-asteroids Pallas and Vesta (though those are borderline cases). Among these bodies, only

3003-589: The transit method. In the same year, the Kepler space telescope mission team released a list of 1235 extrasolar planet candidates , including six that are "Earth-size" or "super-Earth-size" (i.e. they have a radius less than twice that of the Earth) and in the habitable zone of their star. Since then, Kepler has discovered hundreds of planets ranging from Moon-sized to super-Earths, with many more candidates in this size range (see image). In 2016, statistical modeling of

3080-451: The Earth has an active surface hydrosphere . Europa is believed to have an active hydrosphere under its ice layer. During the formation of the Solar System, there were many terrestrial planetesimals and proto-planets , but most merged with or were ejected by the four terrestrial planets, leaving only Pallas and Vesta to survive more or less intact. These two were likely both dwarf planets in

3157-605: The IAU delegated a group of astronomers to develop a sufficiently precise definition of the term planet to decide the issue. This was announced as the IAU's Definition of a Planet in the Solar System , adopted on August 24, 2006. At this time, both Eris and Pluto were classified as dwarf planets , a category distinct from the new definition of planet . Brown has since stated his approval of this classification. The IAU subsequently added Eris to its Minor Planet Catalogue , designating it (136199) Eris . Eris has an orbital period of 559 years . Its maximum possible distance from

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3234-400: The JWST support the idea that Eris's surface is continually refreshing, as no signs of ethane , a byproduct of radiolyzed methane, were detected on Eris's surface. Due to the distant and eccentric orbit of Eris, its surface temperature is estimated to vary from about 30 to 56 K (−243.2 to −217.2 °C; −405.7 to −358.9 °F). Even though Eris can be up to three times farther from

3311-550: The Sun than Eris, even though their semimajor axis is larger than that of Eris (67.8 AU). The Eridian orbit is highly eccentric , and brings Eris to within 37.9 AU of the Sun, a typical perihelion for scattered objects . This is within the orbit of Pluto, but still safe from direct interaction with Neptune (~37 AU). Pluto, on the other hand, like other plutinos , follows a less inclined and less eccentric orbit and, protected by orbital resonance , can cross Neptune's orbit. In about 800 years, Eris will be closer to

3388-436: The Sun than Pluto for some time (see the graph at the left). As of 2007, Eris has an apparent magnitude of 18.7, making it bright enough to be detectable to some amateur telescopes . A 200-millimetre (7.9 in) telescope with a CCD can detect Eris under favorable conditions. The reason it had not been noticed until now is its steep orbital inclination; searches for large outer Solar System objects tend to concentrate on

3465-547: The Sun than Pluto, it approaches close enough that some of the ices on the surface might warm enough to sublime to form an atmosphere . Because methane and nitrogen are both highly volatile , their presence shows either that Eris has always resided in the distant reaches of the Solar System, where it is cold enough for methane and nitrogen ice to persist, or that the celestial body has an internal source to replenish gas that escapes from its atmosphere. This contrasts with observations of another discovered TNO, Haumea , which reveal

3542-501: The accepted value for Dysnomia's period at the time—15.774 days —Eris is 27% more massive than Pluto. Using the 2011 occultation results, Eris has a density of 2.52 ± 0.07 g/cm , substantially denser than Pluto, and thus must be composed largely of rocky materials. Models of internal heating via radioactive decay suggest that Eris could have a subsurface ocean of liquid water at the mantle–core boundary. Tidal heating of Eris by its moon Dysnomia may additionally contribute to

3619-502: The catalog of known exoplanets has increased significantly, and there have been several published refinements of the mass-radius model. As of 2024, the expected transition point between rocky and intermediate-mass planets sits at roughly 4.4 earth masses, and roughly 1.6 earth radii. In September 2020, astronomers using microlensing techniques reported the detection , for the first time, of an Earth-mass rogue planet (named OGLE-2016-BLG-1928 ) unbounded by any star, and free-floating in

3696-442: The chaos following the controversy over the discovery of Haumea, forgot to change it. Rather than needlessly anger more of his fellow astronomers, he simply said that the webpage had been named for his daughter and dropped "Lila" from consideration. Brown had also speculated that Persephone , the wife of the god Pluto , would be a good name for the object. The name had been used several times for planets in science fiction and

3773-542: The discovery of several other large TNOs, including the dwarf planets Quaoar , Orcus , and Sedna . Routine observations were taken by the team on October 21, 2003, using the 1.2 m Samuel Oschin Schmidt telescope at Palomar Observatory , California, but the image of Eris was not discovered at that point due to its very slow motion across the sky: The team's automatic image-searching software excluded all objects moving at less than 1.5  arcseconds per hour to reduce

3850-475: The distance from the Sun increases, consistent with the temperature gradient that would have existed within the primordial solar nebula. The Galilean satellites show a similar trend going outwards from Jupiter; however, no such trend is observable for the icy satellites of Saturn or Uranus. The icy worlds typically have densities less than 2 g·cm . Eris is significantly denser ( 2.43 ± 0.05 g·cm ), and may be mostly rocky with some surface ice, like Europa. It

3927-453: The early 1990s, the first extrasolar planets were discovered orbiting the pulsar PSR B1257+12 , with masses of 0.02, 4.3, and 3.9 times that of Earth, by pulsar timing . When 51 Pegasi b , the first planet found around a star still undergoing fusion , was discovered, many astronomers assumed it to be a gigantic terrestrial, because it was assumed no gas giant could exist as close to its star (0.052 AU) as 51 Pegasi b did. It

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4004-459: The ecliptic plane, where most bodies are found. Because of the high inclination of its orbit, Eris passes through only a few constellations of the traditional Zodiac ; it is now in the constellation Cetus . It was in Sculptor from 1876 until 1929 and Phoenix from roughly 1840 until 1875. In 2036, it will enter Pisces and stay there until 2065, when it will enter Aries . It will then move into

4081-564: The eight planets, whose orbits all lie roughly in the same plane as the Earth's, Eris's orbit is highly inclined : it is tilted at an angle of about 44  degrees to the ecliptic . When discovered, Eris and its moon were the most distant known objects in the Solar System, apart from long-period comets and space probes . It retained this distinction until the discovery of 2018 VG 18 in 2018. As of 2008, there were approximately forty known TNOs , most notably 2006 SQ 372 , 2000 OO 67 and Sedna , that are currently closer to

4158-475: The habitable zone of the star, so they could potentially be habitable, with Earth-like temperatures. Another possibly terrestrial planet, HD 85512 b , was discovered in 2011; it has at least 3.6 times the mass of Earth. The radius and composition of all these planets are unknown. The first confirmed terrestrial exoplanet , Kepler-10b , was found in 2011 by the Kepler space telescope , specifically designed to discover Earth-size planets around other stars using

4235-457: The inner edge of the Kuiper belt were scattered into orbits with higher inclinations than objects from the outer belt. Because Eris was initially thought to be larger than Pluto , it was described as the " tenth planet " by NASA and in media reports of its discovery. In response to the uncertainty over its status, and because of ongoing debate over whether Pluto should be classified as a planet ,

4312-492: The mass of Earth and orbits a star about 21,000 light-years away in the constellation Scorpius. From 2007 to 2010, three (possibly four) potential terrestrial planets were found orbiting within the Gliese 581 planetary system . The smallest, Gliese 581e , is only about 1.9 Earth masses, but orbits very close to the star. Two others, Gliese 581c and the disputed Gliese 581d , are more-massive super-Earths orbiting in or close to

4389-407: The most distant known natural objects in the Solar System until the discovery of 2018 AG 37 and 2018 VG 18 in 2018. Because Eris appeared to be larger than Pluto, NASA initially described it as the Solar System's tenth planet . This, along with the prospect of other objects of similar size being discovered in the future, motivated the International Astronomical Union (IAU) to define

4466-430: The newly commissioned laser guide star adaptive optics system. Images taken on September 10 revealed a moon in orbit around Eris. In keeping with the "Xena" nickname already in use for Eris, Brown's team nicknamed the moon " Gabrielle ", after the television warrior princess's sidekick. When Eris received its official name from the IAU, the moon received the name Dysnomia , after the Greek goddess of lawlessness who

4543-424: The number of false positives returned. When Sedna was discovered in 2003, it was moving at 1.75 arcsec/h, and in light of that the team reanalyzed their old data with a lower limit on the angular motion, sorting through the previously excluded images by eye. In January 2005, the re-analysis revealed Eris's slow orbital motion against the background stars . Follow-up observations were then carried out to make

4620-449: The object had been considered a planet for so long, it deserved a name from Greek or Roman mythology like the other planets. The asteroids had taken the vast majority of Graeco-Roman names. Eris , whom Brown described as his favorite goddess, had fortunately escaped inclusion. "Eris caused strife and discord by causing quarrels among people," said Brown in 2006, "and that's what this one has done too." The usage of planetary symbols

4697-464: The past, but have been battered out of equilibrium shapes by impacts. Some other protoplanets began to accrete and differentiate but suffered catastrophic collisions that left only a metallic or rocky core, like 16 Psyche or 8 Flora respectively. Many S-type and M-type asteroids may be such fragments. The other round bodies from the asteroid belt outward are geophysically icy planets . They are similar to terrestrial planets in that they have

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4774-407: The presence of water ice but not methane. Eris displays very little variation in brightness as it rotates due to its uniform surface, making measurement of its rotation period difficult. Precise long-term monitoring of Eris's brightness indicates that it is tidally locked to its moon Dysnomia, with a rotation period synchronous with the moon's orbital period of 15.78 Earth days. Dysnomia

4851-487: The preservation of its possible subsurface ocean. More research concluded that Eris, Pluto and Makemake could harbor active subsurface oceans and show active geothermal activity. In July 2015, after nearly a decade of Eris being thought to be the ninth-largest known object to directly orbit the Sun, close-up imagery from the New Horizons mission determined the volume of Pluto to be slightly larger than that of Eris. Eris

4928-450: The relationship between a planet's mass and radius using a broken power law appeared to suggest that the transition point between rocky, terrestrial worlds and mini-Neptunes without a defined surface was in fact very close to Earth and Venus's, suggesting that rocky worlds much larger than our own are in fact quite rare. This resulted in some advocating for the retirement of the term "super-earth" as being scientifically misleading. Since 2016

5005-407: The rules . The standard names are chosen to consciously avoid interpreting the underlying cause of the feature, but rather to describe only its appearance. Terrestrial planets A terrestrial planet , telluric planet , or rocky planet , is a planet that is composed primarily of silicate , rocks or metals . Within the Solar System , the terrestrial planets accepted by the IAU are

5082-433: The surface of Eris appears almost white and uniform. Pluto's reddish color is thought to be due to deposits of tholins on its surface, and where these deposits darken the surface, the lower albedo leads to higher temperatures and the evaporation of methane deposits. In contrast, Eris is far enough from the Sun that methane can condense onto its surface even where the albedo is low. The condensation of methane uniformly over

5159-406: The surface reduces any albedo contrasts and would cover up any deposits of red tholins. This methane sublimation and condensation cycle could produce bladed terrain on Eris, similar to those on Pluto. Alternatively, Eris's surface could be refreshed through radiogenic convection of a global methane and nitrogen ice glacier, similar to Pluto's Sputnik Planitia . Spectroscopic observations by

5236-455: The term planet for the first time. Under the IAU definition approved on August 24, 2006, Eris, Pluto and Ceres are " dwarf planets ", reducing the number of known planets in the Solar System to eight, the same as before Pluto's discovery in 1930. Observations of a stellar occultation by Eris in 2010 showed that it was slightly smaller than Pluto, which was measured by New Horizons as having

5313-571: The time was the only TNO known to have surface methane, and of Neptune's moon Triton , which also has methane on its surface. In 2022, near-infrared spectroscopy of Eris by the James Webb Space Telescope (JWST) revealed the presence of deuterated methane ice on its surface, at abundances lower than those in Jupiter-family comets like 67P/Churyumov–Gerasimenko . Eris's comparatively low deuterium abundance suggests that its methane

5390-558: The time, the TV ;show was still on TV, which shows you how long we've been searching! Brown said in an interview that the naming process was stalled: One reporter [Ken Chang] called me up from The New York Times who happened to have been a friend of mine from college, [and] ... asked me, "What's the name you guys proposed?" and I said, "Well, I'm not going to tell." And he said, "Well, what do you guys call it when you're just talking amongst yourselves?" ... As far as I remember this

5467-636: Was 30% land and 70% ocean, only make up 1% of these worlds. Several possible classifications for solid planets have been proposed. Solar System   → Local Interstellar Cloud   → Local Bubble   → Gould Belt   → Orion Arm   → Milky Way   → Milky Way subgroup   → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster   → Local Hole   → Observable universe   → Universe Each arrow ( → ) may be read as "within" or "part of". Eris (dwarf planet)#Xena Eris ( minor-planet designation : 136199 Eris )

5544-478: Was Eris's daughter. Brown says he picked it for similarity to his wife's name, Diane. The name also retains an oblique reference to Eris's old informal name Xena , portrayed on television by Lucy Lawless , though the connection was unintentional. Eris was observed from afar by the outbound New Horizons spacecraft in May 2020, as part of its extended mission following its successful Pluto flyby in 2015. Although Eris

5621-483: Was farther from New Horizons (112 AU) than it was from Earth (96 AU), the spacecraft's unique vantage point inside the Kuiper belt permitted observations of Eris at high phase angles that are otherwise unobtainable from Earth, enabling the determination of the light scattering properties and phase curve behavior of the Eridian surface. In the 2010s, there were multiple studies for follow-on missions to explore

5698-426: Was later found to be a gas giant. In 2005, the first planets orbiting a main-sequence star and which showed signs of being terrestrial planets were found: Gliese 876 d and OGLE-2005-BLG-390Lb . Gliese 876 d orbits the red dwarf Gliese 876 , 15 light years from Earth, and has a mass seven to nine times that of Earth and an orbital period of just two Earth days. OGLE-2005-BLG-390Lb has about 5.5 times

5775-451: Was mindful of not making his name public before it had been officially accepted. He had done so with Sedna a year previously, and had been heavily criticized. However, no objection was raised to the Sedna name other than the breach of protocol, and no competing names were suggested for Sedna. He listed the address of his personal web page announcing the discovery as /~mbrown/planetlila and in

5852-422: Was popular with the public, having handily won a poll conducted by New Scientist magazine. ("Xena", despite only being a nickname, came fourth.) This choice was not possible because there was already a minor planet with that name, 399 Persephone . The discovery team proposed Eris on September 6, 2006. On September 13, 2006, this was accepted as the official name by the IAU. Brown decided that, because

5929-483: Was the only time I told anybody this in the press, and then it got everywhere, which I only sorta felt bad about; I kinda like the name. According to science writer Govert Schilling , Brown initially wanted to call the object " Lila ", after a concept in Hindu mythology that described the cosmos as the outcome of a game played by Brahman . The name could be pronounced like "Lilah", the name of Brown's newborn daughter. Brown

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