125-583: Eridian can refer to: an adjective, related to Eris , a dwarf planet in the Solar System; an ancient, extinct alien species from the Borderlands series; an alien species from the book Project Hail Mary by Andy Weir. Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title Eridian . If an internal link led you here, you may wish to change
250-433: A mantle of hydrated silicates and no core. Because Dawn lacked a magnetometer , it is not known if Ceres has a magnetic field ; it is believed not to. Ceres's internal differentiation may be related to its lack of a natural satellite , as satellites of main belt asteroids are mostly believed to form from collisional disruption, creating an undifferentiated, rubble pile structure. The surface composition of Ceres
375-605: 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
500-641: A naturally dark and clear night sky around new moon . An occultation of the star BD+8°471 by Ceres was observed on 13 November 1984 in Mexico, Florida and across the Caribbean , allowing better measurements of its size, shape and albedo. On 25 June 1995, Hubble obtained ultraviolet images of Ceres with 50 km (30 mi) resolution. In 2002, the Keck Observatory obtained infrared images with 30 km (20 mi) resolution using adaptive optics . Before
625-424: A rare-earth element discovered in 1803, was named after the dwarf planet Ceres. The old astronomical symbol of Ceres, still used in astrology, is a sickle , [REDACTED] . The sickle was one of the classical symbols of the goddess Ceres and was suggested, apparently independently, by von Zach and Bode in 1802. It is similar in form to the symbol ⟨♀⟩ (a circle with a small cross beneath) of
750-450: 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
875-426: A denser mantle of hydrated silicates. A range of densities for the crust and mantle can be calculated from the types of meteorite thought to have impacted Ceres. With CI-class meteorites (density 2.46 g/cm ), the crust would be approximately 70 km (40 mi) thick and have a density of 1.68 g/cm ; with CM-class meteorites (density 2.9 g/cm ), the crust would be approximately 190 km (120 mi) thick and have
1000-754: A density of 1.9 g/cm . Best-fit modelling yields a crust approximately 40 km (25 mi) thick with a density of approximately 1.25 g/cm , and a mantle/core density of approximately 2.4 g/cm . In 2017, Dawn confirmed that Ceres has a transient atmosphere of water vapour. Hints of an atmosphere had appeared in early 2014, when the Herschel Space Observatory detected localised mid-latitude sources of water vapour on Ceres, no more than 60 km (40 mi) in diameter, which each give off approximately 10 molecules (3 kg) of water per second. Two potential source regions, designated Piazzi (123°E, 21°N) and Region A (231°E, 23°N), were visualised in
1125-547: 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
1250-524: A formula later known as the Titius–Bode law that appeared to predict the orbits of the known planets but for an unexplained gap between Mars and Jupiter. This formula predicted that there ought to be another planet with an orbital radius near 2.8 astronomical units (AU), or 420 million km, from the Sun. The Titius–Bode law gained more credence with William Herschel 's 1781 discovery of Uranus near
1375-502: A heavily cratered surface, though with fewer large craters than expected. Models based on the formation of the current asteroid belt had predicted Ceres should have ten to fifteen craters larger than 400 km (250 mi) in diameter. The largest confirmed crater on Ceres, Kerwan Basin , is 284 km (176 mi) across. The most likely reason for this is viscous relaxation of the crust slowly flattening out larger impacts. Ceres's north polar region shows far more cratering than
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#17328763866621500-405: A large amount of sodium carbonate ( Na 2 CO 3 ) and smaller amounts of ammonium chloride ( NH 4 Cl ) or ammonium bicarbonate ( NH 4 HCO 3 ). These materials have been suggested to originate from the crystallisation of brines that reached the surface. In August 2020 NASA confirmed that Ceres was a water-rich body with a deep reservoir of brine that percolated to
1625-413: A large core, the core–mantle boundary should be warm enough for pockets of brine. With a small core, the mantle should remain liquid below 110 km (68 mi). In the latter case a 2% freezing of the liquid reservoir would compress the liquid enough to force some to the surface, producing cryovolcanism. A second two-layer model suggests a partial differentiation of Ceres into a volatile-rich crust and
1750-427: 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
1875-402: A new method of placing numbers before their names in order of discovery. The numbering system initially began with the fifth asteroid, 5 Astraea , as number 1, but in 1867, Ceres was adopted into the new system under the name 1 Ceres. By the 1860s, astronomers widely accepted that a fundamental difference existed between the major planets and asteroids such as Ceres, though
2000-538: 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
2125-442: A planet". Had this resolution been adopted, it would have made Ceres the fifth planet in order from the Sun, but on 24 August 2006 the assembly adopted the additional requirement that a planet must have " cleared the neighbourhood around its orbit". Ceres is not a planet because it does not dominate its orbit, sharing it as it does with the thousands of other asteroids in the asteroid belt and constituting only about forty per cent of
2250-487: A planet. A proposal before the International Astronomical Union (IAU), the global body responsible for astronomical nomenclature and classification, defined a planet as "a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid-body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of
2375-407: 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
2500-775: A rocky core and icy mantle, or even a liquid water ocean, soon after its formation. This ocean should have left an icy layer under the surface as it froze. The fact that Dawn found no evidence of such a layer suggests that Ceres's original crust was at least partially destroyed by later impacts thoroughly mixing the ice with the salts and silicate-rich material of the ancient seafloor and the material beneath. Ceres possesses surprisingly few large craters, suggesting that viscous relaxation and cryovolcanism have erased older geological features. The presence of clays and carbonates requires chemical reactions at temperatures above 50 °C, consistent with hydrothermal activity. It has become considerably less geologically active over time, with
2625-462: A star, Piazzi had found a moving starlike object, which he first thought was a comet. Piazzi observed Ceres twenty-four times, the final sighting occurring on 11 February 1801, when illness interrupted his work. He announced his discovery on 24 January 1801 in letters to two fellow astronomers, his compatriot Barnaba Oriani of Milan and Bode in Berlin . He reported it as a comet, but "since its movement
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#17328763866622750-408: A stronger resemblance to pit crater chains , which are indicative of buried normal faults . Also, several craters on Ceres have shallow, fractured floors consistent with cryomagmatic intrusion. Ceres has one prominent mountain, Ahuna Mons ; this appears to be a cryovolcano and has few craters, suggesting a maximum age of 240 million years. Its relatively high gravitational field suggests it
2875-456: A surface dominated by impact craters ; nevertheless, evidence from Dawn reveals that internal processes have continued to sculpt Ceres's surface to a significant extent contrary to predictions that Ceres's small size would have ceased internal geological activity early in its history. Although Ceres is not as actively discussed as a potential home for microbial extraterrestrial life as Mars , Europa , Enceladus , or Titan are, it has
3000-416: A water exosphere half-life of 7 hours from the ballistic trajectory model, an outgassing rate of 6 kg/s with an optically thin atmosphere sustained for tens of days using a DSMC model, and seasonal polar caps formed from exosphere water delivery using the polar cap model. The mobility of water molecules within the exosphere is dominated by ballistic hops coupled with interaction of the surface, however less
3125-533: 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
3250-480: Is 9 hours and 4 minutes; the small equatorial crater of Kait is selected as its prime meridian . Ceres has an axial tilt of 4°, small enough for its polar regions to contain permanently shadowed craters that are expected to act as cold traps and accumulate water ice over time, similar to what occurs on the Moon and Mercury . About 0.14% of water molecules released from the surface are expected to end up in
3375-471: Is a dwarf planet in the middle main asteroid belt between the orbits of Mars and Jupiter . It was the first known asteroid , discovered on 1 January 1801 by Giuseppe Piazzi at Palermo Astronomical Observatory in Sicily , and announced as a new planet . Ceres was later classified as an asteroid and then a dwarf planet, the only one not beyond Neptune 's orbit. Ceres' diameter is about one-fourth that of
3500-440: Is a mixture of ice, salts, and hydrated minerals. Under that is a layer that may contain a small amount of brine. This extends to a depth of at least the 100 km (60 mi) limit of detection. Under that is thought to be a mantle dominated by hydrated rocks such as clays. In one two-layer model, Ceres consists of a core of chondrules and a mantle of mixed ice and micron-sized solid particulates ("mud"). Sublimation of ice at
3625-553: 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
3750-503: Is also the largest single geographical feature on Ceres. Two of the three have higher than average ammonium concentrations. Dawn observed 4,423 boulders larger than 105 m (344 ft) in diameter on the surface of Ceres. These boulders likely formed through impacts, and are found within or near craters, though not all craters contain boulders. Large boulders are more numerous at higher latitudes. Boulders on Ceres are brittle and degrade rapidly due to thermal stress (at dawn and dusk,
3875-475: 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
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4000-520: Is dense, and thus composed more of rock than ice, and that its placement is likely due to diapirism of a slurry of brine and silicate particles from the top of the mantle. It is roughly antipodal to Kerwan Basin. Seismic energy from the Kerwan-forming impact may have focused on the opposite side of Ceres, fracturing the outer layers of the crust and triggering the movement of high-viscosity cryomagma (muddy water ice softened by its content of salts) onto
4125-521: 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
4250-508: Is evidently the result of space weathering on Ceres's older surfaces; the latter two are volatile under Cererian conditions and would be expected to either escape quickly or settle in cold traps, and so are evidently associated with areas with relatively recent geological activity. Organic compounds were detected in Ernutet Crater, and most of the planet's near surface is rich in carbon, at approximately 20% by mass. The carbon content
4375-414: Is farther from the Sun in its orbit, and internally powered emissions should not be affected by its orbital position. The limited data previously available suggested cometary-style sublimation, but evidence from Dawn suggests geologic activity could be at least partially responsible. Studies using Dawn's gamma ray and neutron detector (GRaND) reveal that Ceres accelerates electrons from the solar wind;
4500-463: Is homogeneous on a global scale, and it is rich in carbonates and ammoniated phyllosilicates that have been altered by water, though water ice in the regolith varies from approximately 10% in polar latitudes to much drier, even ice-free, in the equatorial regions. Studies using the Hubble Space Telescope show graphite , sulfur , and sulfur dioxide on Ceres's surface. The graphite
4625-440: Is known about direct interactions with planetary regoliths. Ceres is a surviving protoplanet that formed 4.56 billion years ago; alongside Pallas and Vesta, one of only three remaining in the inner Solar System, with the rest either merging to form terrestrial planets , being shattered in collisions or being ejected by Jupiter. Despite Ceres's current location, its composition is not consistent with having formed within
4750-399: Is moderately tilted relative to that of Earth; its inclination ( i ) is 10.6°, compared to 7° for Mercury and 17° for Pluto. It is also slightly elongated, with an eccentricity ( e ) = 0.08, compared to 0.09 for Mars. Ceres is not part of an asteroid family , probably due to its large proportion of ice, as smaller bodies with the same composition would have sublimated to nothing over
4875-475: Is more than five times higher than in carbonaceous chondrite meteorites analysed on Earth. The surface carbon shows evidence of being mixed with products of rock-water interactions, such as clays. This chemistry suggests Ceres formed in a cold environment, perhaps outside the orbit of Jupiter, and that it accreted from ultra-carbon-rich materials in the presence of water, which could provide conditions favourable to organic chemistry. Dawn revealed that Ceres has
5000-621: 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
5125-506: 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,
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5250-501: 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
5375-415: 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
5500-533: Is so slow and rather uniform, it has occurred to me several times that it might be something better than a comet". In April, Piazzi sent his complete observations to Oriani, Bode, and French astronomer Jérôme Lalande . The information was published in the September 1801 issue of the Monatliche Correspondenz . By this time, the apparent position of Ceres had changed (primarily due to Earth's motion around
5625-528: 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
5750-513: Is the largest asteroid. The IAU has been equivocal on the subject, though its Minor Planet Center , the organisation charged with cataloguing such objects, notes that dwarf planets may have dual designations, and the joint IAU/ USGS /NASA Gazetteer categorises Ceres as both asteroid and a dwarf planet. Ceres follows an orbit between Mars and Jupiter, near the middle of the asteroid belt, with an orbital period (year) of 4.6 Earth years. Compared to other planets and dwarf planets, Ceres's orbit
5875-504: 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
6000-494: 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
6125-476: Is too dim to be visible to the average naked eye , but under ideal viewing conditions, keen eyes may be able to see it. Vesta is the only other asteroid that can regularly reach a similarly bright magnitude, while Pallas and 7 Iris do so only when both in opposition and near perihelion. When in conjunction , Ceres has a magnitude of around +9.3, which corresponds to the faintest objects visible with 10×50 binoculars; thus, it can be seen with such binoculars in
6250-467: Is unstable at distances less than 5 AU from the Sun, so it is expected to sublime if exposed directly to solar radiation. Proton emission from solar flares and CMEs can sputter exposed ice patches on the surface, leading to a positive correlation between detections of water vapour and solar activity. Water ice can migrate from the deep layers of Ceres to the surface, but it escapes in a short time. Surface sublimation would be expected to be lower when Ceres
6375-509: The Dawn mission, only a few surface features had been unambiguously detected on Ceres. High-resolution ultraviolet Hubble images in 1995 showed a dark spot on its surface, which was nicknamed "Piazzi" in honour of the discoverer of Ceres. It was thought to be a crater. Visible-light images of a full rotation taken by Hubble in 2003 and 2004 showed eleven recognisable surface features, the natures of which were undetermined. One of them corresponded to
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#17328763866626500-407: The Dawn spacecraft found a mean diameter of 939.4 km (583.7 mi) and a mass of 9.38 × 10 kg . This gives Ceres a density of 2.16 g/cm , suggesting that a quarter of its mass is water ice. Ceres makes up 40% of the estimated (2394 ± 5) × 10 kg mass of the asteroid belt, and it has 3 + 1 ⁄ 2 times the mass of the next asteroid, Vesta , but it is only 1.3%
6625-464: The Moon . Its small size means that even at its brightest it is too dim to be seen by the naked eye , except under extremely dark skies. Its apparent magnitude ranges from 6.7 to 9.3, peaking at opposition (when it is closest to Earth ) once every 15- to 16-month synodic period . As a result, its surface features are barely visible even with the most powerful telescopes, and little was known about it until
6750-538: 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
6875-527: The asteroids Pallas , Juno , and Vesta . One of the astronomers selected for the search was Giuseppe Piazzi , a Catholic priest at the academy of Palermo, Sicily . Before receiving his invitation to join the group, Piazzi discovered Ceres on 1 January 1801. He was searching for "the 87th [star] of the Catalogue of the Zodiacal stars of Mr la Caille ", but found that "it was preceded by another". Instead of
7000-484: The near infrared as dark areas (Region A also has a bright centre) by the Keck Observatory . Possible mechanisms for the vapour release are sublimation from approximately 0.6 km (0.2 sq mi) of exposed surface ice, cryovolcanic eruptions resulting from radiogenic internal heat, or pressurisation of a subsurface ocean due to thickening of an overlying layer of ice. In 2015, David Jewitt included Ceres in his list of active asteroids . Surface water ice
7125-458: 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
7250-402: The "missing planet" he had proposed to exist between Mars and Jupiter. Ceres was assigned a planetary symbol and remained listed as a planet in astronomy books and tables (along with Pallas, Juno, and Vesta) for over half a century. As other objects were discovered in the neighbourhood of Ceres, astronomers began to suspect that it represented the first of a new class of objects. When Pallas
7375-507: The 18th century and the discovery of Neptune in 1846, several astronomers argued that mathematical laws predicted the existence of a hidden or missing planet between the orbits of Mars and Jupiter . In 1596, theoretical astronomer Johannes Kepler believed that the ratios between planetary orbits would conform to " God's design " only with the addition of two planets: one between Jupiter and Mars and one between Venus and Mercury. Other theoreticians, such as Immanuel Kant , pondered whether
7500-605: 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
7625-400: 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
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#17328763866627750-835: The Kuiper belt, among which Eris was evaluated as a candidate. It was calculated that a flyby mission to Eris would take 24.66 years using a Jupiter gravity-assist, based on launch dates of April 3, 2032, or April 7, 2044. Eris would be 92.03 or 90.19 AU from the Sun when the spacecraft arrives. 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". Ceres (dwarf planet) Ceres ( minor-planet designation : 1 Ceres )
7875-522: The Piazzi feature. Near-infrared images over a whole rotation, taken with adaptive optics by the Keck Observatory in 2012, showed bright and dark features moving with Ceres's rotation. Two dark features were circular and were presumed to be craters; one was observed to have a bright central region, and the other was identified as the Piazzi feature. Dawn eventually revealed Piazzi to be a dark region in
8000-550: 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
8125-436: 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
8250-547: 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
8375-446: The Sun) and was too close to the Sun's glare for other astronomers to confirm Piazzi's observations. Towards the end of the year, Ceres should have been visible again, but after such a long time, it was difficult to predict its exact position. To recover Ceres, mathematician Carl Friedrich Gauss , then twenty-four years old, developed an efficient method of orbit determination . He predicted
8500-501: 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
8625-433: The age of the Solar System. Ceres is the largest asteroid in the main asteroid belt. It has been classified as a C‑type or carbonaceous asteroid and, due to the presence of clay minerals, as a G-type asteroid . It has a similar, but not identical, composition to that of carbonaceous chondrite meteorites. It is an oblate spheroid, with an equatorial diameter 8% larger than its polar diameter. Measurements from
8750-555: The age of the Solar System. It was once thought to be a member of the Gefion family , the members of which share similar proper orbital elements , suggesting a common origin through an asteroid collision in the past. Ceres was later found to have a different composition from the Gefion family and appears to be an interloper , having similar orbital elements but not a common origin. Due to their small masses and large separations, objects within
8875-597: The asteroid belt rarely fall into gravitational resonances with each other. Nevertheless, Ceres is able to capture other asteroids into temporary 1:1 resonances (making them temporary trojans ), for periods from a few hundred thousand to more than two million years. Fifty such objects have been identified. Ceres is close to a 1:1 mean-motion orbital resonance with Pallas (their proper orbital periods differ by 0.2%), but not close enough to be significant over astronomical timescales. The rotation period of Ceres (the Cererian day)
9000-706: The asteroid belt. It seems rather that it formed between the orbits of Jupiter and Saturn, and was deflected into the asteroid belt as Jupiter migrated outward. The discovery of ammonium salts in Occator Crater supports an origin in the outer Solar System, as ammonia is far more abundant in that region. The early geological evolution of Ceres was dependent on the heat sources available during and after its formation: impact energy from planetesimal accretion and decay of radionuclides (possibly including short-lived extinct radionuclides such as aluminium-26 ). These may have been sufficient to allow Ceres to differentiate into
9125-409: The belt's total mass. Bodies that met the first proposed definition but not the second, such as Ceres, were instead classified as dwarf planets . Planetary geologists still often ignore this definition and consider Ceres to be a planet anyway. Ceres is a dwarf planet, but there is some confusion about whether it is also an asteroid. A NASA webpage states that Vesta, the belt's second-largest object,
9250-473: The bright spots. In March 2016 Dawn found definitive evidence of water ice on the surface of Ceres at Oxo crater . On 9 December 2015, NASA scientists reported that the bright spots on Ceres may be due to a type of salt from evaporated brine containing magnesium sulfate hexahydrate (MgSO 4 ·6H 2 O); the spots were also found to be associated with ammonia-rich clays. Near-infrared spectra of these bright areas were reported in 2017 to be consistent with
9375-442: 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
9500-479: The course of the last three million years has triggered cyclical shifts in Ceres's axial tilt, ranging from two to twenty degrees, meaning that seasonal variation in sun exposure has occurred in the past, with the last period of seasonal activity estimated at 14,000 years ago. Those craters that remain in shadow during periods of maximum axial tilt are the most likely to retain water ice from eruptions or cometary impacts over
9625-399: The crust. Models suggest that, over the past billion years, one cryovolcano has formed on Ceres on average every fifty million years. The eruptions may be linked to ancient impact basins but are not uniformly distributed over Ceres. The model suggests that, contrary to findings at Ahuna Mons, Cererian cryovolcanoes must be composed of far less dense material than average for Ceres's crust, or
9750-631: The densities of the core and mantle/crust to be 2.46–2.90 and 1.68–1.95 g/cm respectively, with the mantle and crust together being 70–190 km (40–120 mi) thick. Only partial dehydration (expulsion of ice) from the core is expected, though the high density of the mantle relative to water ice reflects its enrichment in silicates and salts. That is, the core (if it exists), the mantle and crust all consist of rock and ice, though in different ratios. Ceres's mineral composition can be determined (indirectly) only for its outer 100 km (60 mi). The solid outer crust, 40 km (25 mi) thick,
9875-542: 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
10000-459: 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
10125-612: 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
10250-594: The equatorial region, with the eastern equatorial region in particular comparatively lightly cratered. The overall size frequency of craters of between twenty and a hundred kilometres (10–60 mi) is consistent with their having originated in the Late Heavy Bombardment , with craters outside the ancient polar regions likely erased by early cryovolcanism . Three large shallow basins (planitiae) with degraded rims are likely to be eroded craters. The largest, Vendimia Planitia , at 800 km (500 mi) across,
10375-487: The gap had been created by the gravity of Jupiter; in 1761, astronomer and mathematician Johann Heinrich Lambert asked: "And who knows whether already planets are missing which have departed from the vast space between Mars and Jupiter? Does it then hold of celestial bodies as well as of the Earth, that the stronger chafe the weaker, and are Jupiter and Saturn destined to plunder forever?" In 1772, German astronomer Johann Elert Bode , citing Johann Daniel Titius , published
10500-404: The group of bright spots to its east, Vinalia Faculae. Occator possesses a pit 9–10 km wide, partially filled by a central dome. The dome post-dates the faculae and is likely due to freezing of a subterranean reservoir, comparable to pingos in Earth's Arctic region. A haze periodically appears above Cerealia, supporting the hypothesis that some sort of outgassing or sublimating ice formed
10625-408: 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 ,
10750-422: The law was a coincidence. The early observers were able to calculate the size of Ceres only to within an order of magnitude . Herschel underestimated its diameter at 260 km (160 mi) in 1802; in 1811, German astronomer Johann Hieronymus Schröter overestimated it as 2,613 km (1,624 mi). In the 1970s, infrared photometry enabled more accurate measurements of its albedo , and Ceres's diameter
10875-419: The link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Eridian&oldid=1253315805 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Eris (dwarf planet) Eris ( minor-planet designation : 136199 Eris )
11000-416: The mass of the Moon . It is close to being in hydrostatic equilibrium , but some deviations from an equilibrium shape have yet to be explained. Regardless, Ceres is the only widely accepted dwarf planet with an orbital period less than that of Neptune. Modelling has suggested Ceres's rocky material is partially differentiated , and that it may possess a small core , but the data is also consistent with
11125-479: The most accepted hypothesis is that these electrons are being accelerated by collisions between the solar wind and a tenuous water vapour exosphere. Bow shocks like these could also be explained by a transient magnetic field, but this is considered less likely, as the interior of Ceres is not thought to be sufficiently electrically conductive. Ceres' thin exosphere is continuously replenished through exposure of water ice patches by impacts, water ice diffusion through
11250-407: 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
11375-417: The most water of any body in the inner Solar System after Earth, and the likely brine pockets under its surface could provide habitats for life. Unlike Europa or Enceladus, it does not experience tidal heating , but it is close enough to the Sun, and contains enough long-lived radioactive isotopes, to preserve liquid water in its subsurface for extended periods. The remote detection of organic compounds and
11500-430: 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
11625-424: 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
11750-449: 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
11875-401: The observed viscous relaxation could not occur. An unexpectedly large number of Cererian craters have central pits, perhaps due to cryovolcanic processes; others have central peaks. Hundreds of bright spots (faculae) have been observed by Dawn , the brightest in the middle of 80 km (50 mi) Occator Crater . The bright spot in the centre of Occator is named Cerealia Facula, and
12000-401: The outer mantle and reach the surface, allowing cryovolcanoes such as Ahuna Mons to form roughly every fifty million years. This makes Ceres the closest known cryovolcanically active body to the Sun . Additionally, Ceres hosts an extremely tenuous and transient atmosphere of water vapour, vented from localised sources on its surface. In the years between the acceptance of heliocentrism in
12125-473: The path of Ceres within a few weeks and sent his results to von Zach. On 31 December 1801, von Zach and fellow celestial policeman Heinrich W. M. Olbers found Ceres near the predicted position and continued to record its position. At 2.8 AU from the Sun, Ceres appeared to fit the Titius–Bode law almost perfectly; when Neptune was discovered in 1846, eight AU closer than predicted, most astronomers concluded that
12250-442: The planet Venus, but with a break in the circle. It had various minor graphic variants, including a reversed form [REDACTED] typeset as a 'C' (the initial letter of the name Ceres ) with a plus sign. The generic asteroid symbol of a numbered disk, ①, was introduced in 1867 and quickly became the norm. The categorisation of Ceres has changed more than once and has been the subject of some disagreement. Bode believed Ceres to be
12375-515: The porous ice crust and proton sputtering during solar activity. The rate of this vapour diffusion scales with grain size and is heavily affected by a global dust mantle consisting of an aggregate of approximately 1 micron particles. Exospheric replenishment through sublimation alone is very small, with the current outgassing rate being only 0.003 kg/s. Various models of an extant exosphere have been attempted including ballistic trajectory, DSMC , and polar cap numerical models. Results showed
12500-523: The predicted distance for a planet beyond Saturn . In 1800, a group headed by Franz Xaver von Zach , editor of the German astronomical journal Monatliche Correspondenz [ de ] ( Monthly Correspondence ), sent requests to twenty-four experienced astronomers, whom he dubbed the " celestial police ", asking that they combine their efforts and begin a methodical search for the expected planet. Although they did not discover Ceres, they later found
12625-407: 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
12750-459: The presence of water mixed with 20% carbon by mass in its near surface could provide conditions favourable to organic chemistry. Of the biochemical elements, Ceres is rich in carbon , hydrogen , oxygen and nitrogen , but phosphorus has yet to be detected, and sulfur, despite being suggested by Hubble UV observations, was not detected by Dawn . When in opposition near its perihelion , Ceres can reach an apparent magnitude of +6.7. This
12875-487: 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
13000-483: The robotic NASA spacecraft Dawn approached Ceres for its orbital mission in 2015. Dawn found Ceres's surface to be a mixture of water ice and hydrated minerals such as carbonates and clay . Gravity data suggest Ceres to be partially differentiated into a muddy (ice-rock) mantle/core and a less dense but stronger crust that is at most thirty per cent ice by volume. Although Ceres likely lacks an internal ocean of liquid water, brines still flow through
13125-404: The surface has preserved craters almost 300 km (200 mi) in diameter indicates that the outermost layer of Ceres is roughly 1000 times stronger than water ice. This is consistent with a mixture of silicates , hydrated salts and methane clathrates , with no more than 30% water ice by volume. Gravity measurements from Dawn have generated three competing models for Ceres's interior. In
13250-457: The surface in hundreds of locations causing "bright spots", including those in Occator Crater. The active geology of Ceres is driven by ice and brines. Water leached from rock is estimated to possess a salinity of around 5%. Altogether, Ceres is approximately 50% water by volume (compared to 0.1% for Earth) and 73% rock by mass. Ceres's largest craters are several kilometres deep, inconsistent with an ice-rich shallow subsurface. The fact that
13375-433: 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
13500-406: 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
13625-622: The surface temperature changes rapidly) and meteoritic impacts. Their maximum age is estimated to be 150 million years, much shorter than the lifetime of boulders on Vesta. Although Ceres lacks plate tectonics , with the vast majority of its surface features linked either to impacts or to cryovolcanic activity, several potentially tectonic features have been tentatively identified on its surface, particularly in its eastern hemisphere. The Samhain Catenae, kilometre-scale linear fractures on Ceres's surface, lack any apparent link to impacts and bear
13750-424: The surface would leave a deposit of hydrated particulates perhaps twenty metres thick. The range of the extent of differentiation is consistent with the data, from a large, 360 km (220 mi) core of 75% chondrules and 25% particulates and a mantle of 75% ice and 25% particulates, to a small, 85 km (55 mi) core consisting nearly entirely of particulates and a mantle of 30% ice and 70% particulates. With
13875-562: The surface. Kerwan too shows evidence of the effects of liquid water due to impact-melting of subsurface ice. A 2018 computer simulation suggests that cryovolcanoes on Ceres, once formed, recede due to viscous relaxation over several hundred million years. The team identified 22 features as strong candidates for relaxed cryovolcanoes on Ceres's surface. Yamor Mons, an ancient, impact-cratered peak, resembles Ahuna Mons despite being much older, due to it lying in Ceres's northern polar region, where lower temperatures prevent viscous relaxation of
14000-455: 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
14125-488: The three-layer model, Ceres is thought to consist of an outer, 40 km (25 mi) thick crust of ice, salts and hydrated minerals and an inner muddy " mantle " of hydrated rock, such as clays, separated by a 60 km (37 mi) layer of a muddy mixture of brine and rock. It is not possible to tell if Ceres's deep interior contains liquid or a core of dense material rich in metal, but the low central density suggests it may retain about 10% porosity . One study estimated
14250-571: 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
14375-558: 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
14500-490: The traps, hopping an average of three times before escaping or being trapped. Dawn , the first spacecraft to orbit Ceres, determined that the north polar axis points at right ascension 19 h 25 m 40.3 s (291.418°), declination +66° 45' 50" (about 1.5 degrees from Delta Draconis ), which means an axial tilt of 4°. This means that Ceres currently sees little to no seasonal variation in sunlight by latitude. Gravitational influence from Jupiter and Saturn over
14625-413: The word "planet" had yet to be precisely defined . In the 1950s, scientists generally stopped considering most asteroids as planets, but Ceres sometimes retained its status after that because of its planet-like geophysical complexity. Then, in 2006, the debate surrounding Pluto led to calls for a definition of "planet", and the possible reclassification of Ceres, perhaps even its general reinstatement as
14750-478: 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
14875-507: Was determined to within ten per cent of its true value of 939 km (583 mi). Piazzi's proposed name for his discovery was Ceres Ferdinandea : Ceres after the Roman goddess of agriculture , whose earthly home, and oldest temple, lay in Sicily; and Ferdinandea in honour of Piazzi's monarch and patron, King Ferdinand III of Sicily . The latter was not acceptable to other nations and
15000-475: Was discovered in 1802, Herschel coined the term asteroid ("star-like") for these bodies, writing that "they resemble small stars so much as hardly to be distinguished from them, even by very good telescopes". In 1852 Johann Franz Encke , in the Berliner Astronomisches Jahrbuch , declared the traditional system of granting planetary symbols too cumbersome for these new objects and introduced
15125-546: Was dropped. Before von Zach's recovery of Ceres in December 1801, von Zach referred to the planet as Hera , and Bode referred to it as Juno . Despite Piazzi's objections, those names gained currency in Germany before the object's existence was confirmed. Once it was, astronomers settled on Piazzi's name. The adjectival forms of Ceres are Cererian and Cererean , both pronounced / s ɪ ˈ r ɪər i ə n / . Cerium ,
15250-483: 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
15375-451: 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
15500-422: 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
15625-483: 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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