Eris

Eris (centre) and Dysnomia (left of centre). Dysnomia (,, or as in Greek Δυσνομία officially (136199 Eris I Dysnomia, is the only known moon of the Dwarf planet Eris Hubble Space Telescope. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into
Discovery
Discovered by	M. E. Brown, C. A. Trujillo, D. L. Rabinowitz[1]
Discovery date	October 21, 2003[1]
Designations
MPC designation	136199 Eris
Alternative names	2003 UB313[2]
Minor planet category	dwarf planet TNO and SDO
Orbital characteristics
Epoch March 6, 2006 (JD 2453800. Education Brown is a Huntsville Alabama native and graduated from Virgil Grissom High School in 1983 Early career Trujillo attended Oak Park and River Forest High School in Oak Park Illinois. David Lincoln Rabinowitz (born 1960) is a researcher at Yale University. Events 1512 - Martin Luther joins the theological faculty of the University of Wittenberg. Year 2003 ( MMIII) was a Common year starting on Wednesday of the Gregorian calendar. A provisional designation in astronomy is the naming convention applied to Astronomical objects immediately following their discovery A dwarf planet, as defined by the International Astronomical Union (IAU is a Celestial body Orbiting the Sun that is massive enough to be rounded A trans-Neptunian object (TNO is any object in the Solar system that Orbits the sun at a greater distance on average than Neptune. The scattered disc (or scattered disk) is a distant region of the Solar System that is sparsely populated by icy Minor planets known as scattered In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star In Astronomy, an epoch is a moment in time used as a reference for the Orbital elements of a Celestial body. Events 1079 - Omar Khayyám completes the Iranian calendar. 1454 - Thirteen Years' War: Delegates of Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. The Julian date (JD is the interval of time in days and fractions of a day since 4713 B 5)[3]
Aphelion	97. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from 56 AU 14. The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the 60×109km
Perihelion	37. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from 77 AU 5. 65×109 km
Semi-major axis	67. In Geometry, the semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae 6681 AU 10. 12×109 km
Eccentricity	0. In Astrodynamics, under standard assumptions, any Orbit must be of Conic section shape 44177
Orbital period	203,600 days 557 years
Average orbital speed	3. The orbital period is the time taken for a given object to make one complete Orbit about another object In Astronomy, a Julian year (symbol a) is a unit of measurement of Time defined The orbital speed of a body generally a Planet, a Natural satellite, an artificial satellite, or a Multiple star, is the speed at which it 436 km/s
Mean anomaly	197. In the study of orbital dynamics the mean anomaly of an orbiting body is the Angle the body would have traveled about the center of the orbit's Auxiliary circle 63427°
Inclination	44. Inclination in general is the Angle between a Reference plane and another plane or axis of direction 187°
Longitude of ascending node	35. The longitude of the ascending node (☊ or Ω is one of the Orbital elements used to specify the Orbit of an object in space 8696°
Argument of perihelion	151. The argument of periapsis (or argument of perifocus) ( ω) is the Orbital element describing the Angle of an Orbiting body's periapsis 4305°
Satellites	1
Physical characteristics
Mean radius	1,300 +200 -100 km[4]
Mass	(1. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object 67 ± 0. 02)×1022 kg[5]
Equatorial surface gravity	~0. The surface gravity, g, of an astronomical or other object is the Gravitational acceleration experienced at its surface 8 m/s²
Sidereal rotation period	> 8 h?
Albedo	0. The rotation period of an astronomical object is the time it takes to complete one revolution around its Axis of rotation relative to the background stars The albedo of an object is the extent to which it diffusely reflects light from the sun 86 ± 0. 07
Surface temp.    (approx)	min mean max 30 K 42. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic 5 K 55 K
Apparent magnitude	18. The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 7
Absolute magnitude	−1. In Astronomy, absolute magnitude (also known as absolute visual magnitude) is the Apparent magnitude an object would have if it were at a standard 12 ± 0. 01
Angular diameter	40 milli-arcsec[6]

Eris (pronounced /ˈɪərɪs/, also /ˈɛrɪs/ as in Greek Έρις^[7]), formally designated 136199 Eris and formerly 2003 UB₃₁₃ (see minor planet names), is the largest known dwarf planet in the Solar System and the ninth largest body known to orbit the Sun directly. The angular diameter of an object as seen from a given position is the "visual diameter" of the object measured as an angle A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60 of one degree. Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly A dwarf planet, as defined by the International Astronomical Union (IAU is a Celestial body Orbiting the Sun that is massive enough to be rounded The Solar System consists of the Sun and those celestial objects bound to it by Gravity. The Sun (Sol is the Star at the center of the Solar System. It is approximately 2,500 kilometres in diameter and 27% more massive than Pluto. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object ^[8][5]

Eris was first spotted in 2003 by a Palomar Observatory-based team led by Mike Brown but not identified until 2005. Palomar Observatory is a privately owned Observatory located in San Diego County California, 90 miles (145 Km) Southeast of Mount Wilson Education Brown is a Huntsville Alabama native and graduated from Virgil Grissom High School in 1983 It is a trans-Neptunian object (TNO) native to a region of space beyond the Kuiper belt known as the scattered disc. A trans-Neptunian object (TNO is any object in the Solar system that Orbits the sun at a greater distance on average than Neptune. The Kuiper belt (ˈkaɪpɚ to rhyme with "viper" sometimes called the Edgeworth-Kuiper belt, is a region of the Solar System beyond the planets extending The scattered disc (or scattered disk) is a distant region of the Solar System that is sparsely populated by icy Minor planets known as scattered Eris has one moon, Dysnomia; recent observations have found no evidence of further satellites. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. Dysnomia (,, or as in Greek Δυσνομία officially (136199 Eris I Dysnomia, is the only known moon of the Dwarf planet Eris The current distance from the Sun is 96. 7 AU, roughly three times that of Pluto. The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the With the exception of some comets, the pair are the most distant known bodies in the Solar System. A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — ^[9]

Because Eris is larger than Pluto, its discoverers and NASA called it the Solar system’s tenth planet. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program This, along with the prospect of other similarly sized objects being discovered in the future, motivated the International Astronomical Union (IAU) to define the term "planet" for the first time. From its beginnings denoting the "wandering stars" of the classical world the definition of " Planet " has been fraught with ambiguity Under a new definition approved on August 24, 2006, Eris was designated a "dwarf planet" along with Pluto and Ceres. Events 49 BC - Julius Caesar 's General Gaius Scribonius Curio is defeated in the Second Battle of the Bagradas River Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Ceres (ˈsɪəriːz ^[10]

Discovery

Eris was discovered by the team of Mike Brown, Chad Trujillo, and David Rabinowitz^[9] on January 5, 2005, from images taken on October 21, 2003. Education Brown is a Huntsville Alabama native and graduated from Virgil Grissom High School in 1983 Early career Trujillo attended Oak Park and River Forest High School in Oak Park Illinois. David Lincoln Rabinowitz (born 1960) is a researcher at Yale University. Events 1477 - Battle of Nancy: Charles the Bold is killed and Burgundy becomes part of France. Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. Events 1512 - Martin Luther joins the theological faculty of the University of Wittenberg. Year 2003 ( MMIII) was a Common year starting on Wednesday of the Gregorian calendar. The discovery was announced on July 29, 2005, the same day as two other large TNOs, (136108) 2003 EL₆₁ and (136472) 2005 FY₉. Events 1014 - Byzantine-Bulgarian Wars: Battle of Kleidion: Byzantine emperor Basil II inflicts a decisive defeat Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. A trans-Neptunian object (TNO is any object in the Solar system that Orbits the sun at a greater distance on average than Neptune. The search team had been systematically scanning for large outer solar system bodies for several years, and had been involved in the discovery of several other large TNOs, including 50000 Quaoar, 90482 Orcus, and 90377 Sedna. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. TemplateInfobox Planet. --> 90482 Orcus (, Orcus originally known by the Provisional designation TemplateInfobox Planet.--> 90377 Sedna (ˈsɛdnə) is a Trans-Neptunian

Routine observations were taken by the team on October 21, 2003, using the 1200 mm Samuel Oschin reflecting telescope at Mount 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. Events 1512 - Martin Luther joins the theological faculty of the University of Wittenberg. Year 2003 ( MMIII) was a Common year starting on Wednesday of the Gregorian calendar. The Samuel Oschin telescope is a 48-inch (122-m aperture Schmidt camera at the Palomar Observatory in northern San Diego County, California A reflecting telescope (also called a reflector) is an Optical telescope which uses a single or combination of Curved mirrors that reflect Light Palomar Observatory is a privately owned Observatory located in San Diego County California, 90 miles (145 Km) Southeast of Mount Wilson California ( is a US state on the West Coast of the United States, along the Pacific Ocean. 5 arcseconds per hour to reduce the number of false positives returned. A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60 of one degree. In Statistics, the terms Type I error (also α error, or false positive) and type II error ( β error, or a false negative When Sedna was discovered, 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' slow motion against the background stars. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth

Animation showing the movement of Eris on the images used to discover it. Eris is located on the left side, slightly above the middle of the image. The three frames were taken over a period of three hours.

Follow-up observations were then carried out to make a preliminary determination of its orbit, which allowed its distance to be estimated. In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star The team had planned to delay announcing their discovery until further observations allowed more accurate calculations of Eris' orbit, but brought their announcement forward when the discovery of another large TNO they had been tracking, 2003 EL₆₁, was announced by a different team in Spain. Spain () or the Kingdom of Spain (Reino de España is a country located mostly in southwestern Europe on the Iberian Peninsula. ^[9]

More observations released in October 2005 revealed that Eris had a moon, later named Dysnomia. Dysnomia (,, or as in Greek Δυσνομία officially (136199 Eris I Dysnomia, is the only known moon of the Dwarf planet Eris Observations of Dysnomia's orbit permitted scientists to determine the mass of Eris, which in June 2007 they calculated to be (1. 66 ± 0. 02)×10²² kg, 27% greater than Pluto.

Classification

Eris is classified as a dwarf planet and a scattered disk object (SDO). A dwarf planet, as defined by the International Astronomical Union (IAU is a Celestial body Orbiting the Sun that is massive enough to be rounded The scattered disc (or scattered disk) is a distant region of the Solar System that is sparsely populated by icy Minor planets known as scattered The latter is a category of the TNOs that are believed to have been "scattered" from the Kuiper belt into more distant and unusual orbits following gravitational interactions with Neptune as the Solar system was forming. A trans-Neptunian object (TNO is any object in the Solar system that Orbits the sun at a greater distance on average than Neptune. The Kuiper belt (ˈkaɪpɚ to rhyme with "viper" sometimes called the Edgeworth-Kuiper belt, is a region of the Solar System beyond the planets extending In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. Although its high orbital inclination is unusual among the known SDOs, theoretical models suggest that objects that were originally near the inner edge of the Kuiper belt were scattered into orbits with higher inclinations than objects from the outer belt. ^[11] Inner-belt objects are expected to be generally more massive than outer-belt objects, and so astronomers expect to discover more large objects like Eris in high-inclination orbits, which have traditionally been neglected.

Distribution of trans-Neptunian Objects.

As Eris is larger than Pluto, it was initially described as the "tenth planet" by NASA and in media reports of its discovery. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program ^[12] In response to the uncertainty over its status, and because of ongoing debate over whether Pluto should be classified as a planet, the IAU delegated a group of astronomers to develop a sufficiently precise definition of the term planet to decide the issue. A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is This was announced as the IAU's Definition of a Planet in the Solar System, adopted on 24 August 2006. From its beginnings denoting the "wandering stars" of the classical world the definition of " Planet " has been fraught with ambiguity Events 49 BC - Julius Caesar 's General Gaius Scribonius Curio is defeated in the Second Battle of the Bagradas River Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. At this time both Eris and Pluto were classified as dwarf planets, a category distinct from the new definition of planet. A dwarf planet, as defined by the International Astronomical Union (IAU is a Celestial body Orbiting the Sun that is massive enough to be rounded ^[13] Brown has since stated his approval of the "dwarf planet" label. ^[14] The IAU subsequently added Eris to its Minor Planet Catalogue, designating it (136199) Eris. This is a list of numbered Minor planets in sequential order there are 192280 numbered minor planets and many more not yet numbered ^[15]

Name

Athenian painting of Eris, circa 550 BCE

Eris is named after the goddess Eris (Greek Έρις), a personification of strife and discord. Athens (ˈæθənz Αθήνα Athina,) the Capital and largest city of Greece, dominates the Attica periphery as one of the world's Eris ( Greek Ἔρις, "Strife" is the Greek Goddess of strife her name being translated into Latin as Discordia Eris ( Greek Ἔρις, "Strife" is the Greek Goddess of strife her name being translated into Latin as Discordia Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly ^[16] The name was assigned on September 13, 2006 following an unusually long period in which it was known by the provisional designation 2003 UB₃₁₃, which was granted automatically by the IAU under their naming protocols for minor planets. Events 509 BC - The Temple of Jupiter on Rome 's Capitoline Hill is dedicated on the ides of September Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. A provisional designation in astronomy is the naming convention applied to Astronomical objects immediately following their discovery Minor planet is a term used since the 19th century to describe objects such as Asteroids that are in Orbit around the Sun but are not Planets The adjectival form of Eris is Eridian.

Nicknames

Before the name Eris was granted, two nicknames were used in the popular media, Xena and Lila.

“Xena” was an informal name used internally by the discovery team. It was inspired by the eponymous heroine of the television series Xena: Warrior Princess. Xena Warrior Princess is an American Television series that aired from September 15 1995 until June 18 2001 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 (OK, so it’s TV mythology, but Pluto is named after a cartoon, right?),^[a] and (this part is actually true) we've been working to get more female deities out there (i. e. Sedna). TemplateInfobox Planet.--> 90377 Sedna (ˈsɛdnə) is a Trans-Neptunian Also at the time the TV show was still on TV, which shows you how long we've been searching!^[17]

The nickname "Lila" has also been used by the media. However, this was a misunderstanding of planetlila, the URL path of the discovery web page. Uniform Resource Locator is an URI which also specifies where the identified resource is available and the protocol for retrieving it ^[18] The URL path was named after Mike Brown's then-newborn daughter, Lilah. Education Brown is a Huntsville Alabama native and graduated from Virgil Grissom High School in 1983

Choosing an official name

The delay in assigning a name was due to uncertainty over whether the object would be classified as a planet or a minor planet; different nomenclature procedures apply to these different classes of object. A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is Minor planet is a term used since the 19th century to describe objects such as Asteroids that are in Orbit around the Sun but are not Planets ^[19] The decision on a name had to wait until after the August 24, 2006 IAU ruling defining the object as a dwarf planet. Events 49 BC - Julius Caesar 's General Gaius Scribonius Curio is defeated in the Second Battle of the Bagradas River Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. A dwarf planet, as defined by the International Astronomical Union (IAU is a Celestial body Orbiting the Sun that is massive enough to be rounded ^[20]

Brown had previously speculated that Persephone would be a good name for the object. In Greek mythology, Persephone ( Kore or Cora) was the embodiment of the Earth's fertility at the same time that she was the Queen of the Underworld However, this was not possible once the object was classified as a dwarf planet, because there is already an asteroid with that name, 399 Persephone. Asteroids, sometimes called Minor planets or planetoids', are bodies—primarily of the inner Solar System —that are smaller than planets but 399 Persephone is a typical Main belt Asteroid. It was discovered by Max Wolf on February 23, 1895 in Heidelberg. ^[9] Because IAU regulations require a name from creation mythology for objects with orbital stability beyond Neptune’s orbit, the team had also been considering such possibilities. In ancient times only the Sun and Moon, a few hundred Stars and the most easily visible Planets had names A creation myth is a supernatural mytho-[[religion religious]] story or explanation that describes the beginnings of humanity, Earth, life, and Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. ^[18]

The discovery team proposed Eris on 6 September 2006. Events 3114 BC - According to the Proleptic Julian calendar the current era in the Maya Long Count Calendar started Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. On 13 September 2006 it was accepted as the official name by the IAU. Events 509 BC - The Temple of Jupiter on Rome 's Capitoline Hill is dedicated on the ides of September Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. ^[21][18] The name in part reflects the discord in the astronomical community caused by the debate over the object’s (and Pluto’s) nature, while the name of its moon, Dysnomia (“lawlessness”), retains an oblique reference to the dwarf planet’s old informal name Xena, portrayed on TV by Lucy Lawless. Dysnomia (,, or as in Greek Δυσνομία officially (136199 Eris I Dysnomia, is the only known moon of the Dwarf planet Eris Lucy Lawless (born Lucille Frances Ryan; 29 March 1968 is a New Zealand actress and Singer best known for playing the title character

Orbit

The orbit of Eris (blue) compared to those of Saturn, Uranus, Neptune, and Pluto (white/grey). The arcs below the ecliptic are plotted in darker colours, and the red dot is the Sun. The diagram on the left is a polar view while the diagrams on the right are different views from the ecliptic.

Eris has an orbital period of 557 years, and as of 2008 lies at 96. The orbital period is the time taken for a given object to make one complete Orbit about another object 7 astronomical units from the Sun, almost its maximum possible distance. The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the (Its aphelion is 97. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from 5 AU. ) Eris came to perihelion between 1698^[22]-1699,^[23] aphelion around 1977,^[23] and will return to perihelion around 2256^[23] to 2258. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from ^[24] Eris and its moon are currently the most distant known objects in the Solar system apart from long-period comets and space probes. A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — A space probe is a scientific Space exploration mission in which a Robotic spacecraft leaves the Gravity well of Earth and approaches the ^[25] However, approximately forty known TNOs, most notably 2000 OO₆₇ and Sedna, while currently closer to the Sun than Eris, have greater average orbital distances than Eris' semimajor axis of 67. A trans-Neptunian object (TNO is any object in the Solar system that Orbits the sun at a greater distance on average than Neptune. TemplateInfobox Planet.--> 90377 Sedna (ˈsɛdnə) is a Trans-Neptunian In Geometry, the semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae 7 AU. ^[26]

The Eridian orbit is highly eccentric, and brings Eris to within 37. In Astrodynamics, under standard assumptions, any Orbit must be of Conic section shape 9 AU of the Sun, a typical perihelion for scattered objects. The scattered disc (or scattered disk) is a distant region of the Solar System that is sparsely populated by icy Minor planets known as scattered This is within the orbit of Pluto, but still safe from direct interaction with Neptune (29. Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. 8-30. 4 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 Astronomy, a plutino is a Trans-Neptunian object in 23 mean motion resonance with Neptune. In Celestial mechanics, an orbital resonance occurs when two Orbiting bodies exert a regular periodic gravitational influence on each other usually due to their Unlike the terrestrial planets and gas giants, whose orbits all lie roughly in the same plane as the Earth's, Eris' orbit is highly inclined: It is tilted at an angle of about 44 degrees to the ecliptic. A terrestrial planet, telluric planet or rocky planet is a Planet that is primarily composed of Silicate rocks Within our A gas giant (sometimes also known as a Jovian planet after the planet Jupiter, or giant planet) is a large Planet that is not primarily The ecliptic is the apparent path that the Sun traces out in the sky during the year Inclination in general is the Angle between a Reference plane and another plane or axis of direction This article describes the unit of angle For other meanings see Degree.

Eris currently has an apparent magnitude of 18. The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 7, making it bright enough to be detectable to some amateur telescopes. A telescope is an instrument designed for the observation of remote objects and the collection of Electromagnetic radiation. A 200 mm telescope with a CCD can detect Eris under favorable conditions. A charge-coupled device ( CCD) is an analog Shift register, that enables the transportation of analog signals (electric charges through successive stages (capacitors ^[b] The reason it had not been noticed until now is because of its steep orbital inclination; most searches for large outer Solar system objects concentrate on the ecliptic plane, where most bodies are found.

Eris is now in the constellation Cetus. Cetus ( Κῆτος Kētos, referring to the sea monster Cetus) is a Constellation of the northern winter sky in the region known as the Water It was in Sculptor from 1876 until 1929 and Phoenix from roughly 1840 until 1875. Sculptor (ˈskʌlptɚ is a minor southern Constellation which was introduced by Nicolas Louis de Lacaille. Phoenix (ˈfiːnɪks is a minor southern Constellation, introduced by Dutch navigators Pieter Dirkszoon Keyser and Frederick de Houtman, and popularized In 2036 it will enter Pisces and stay there until 2065, when it will enter Aries. Pisces (ˈpaɪsiːz Fish (plural symbol, Unicode ♓ is a Zodiac Constellation which lies between Aquarius to the west and Aries Aries ( ram, symbol, Unicode ♈ is one of the Constellations of the Zodiac. ^[23] It will then move into the northern sky, entering Perseus in 2128 and Camelopardalis (where it will reach its northernmost declination) in 2173. In Astronomy and Navigation, the celestial sphere is an imaginary rotating Sphere of "gigantic Radius " For other meanings see Perseus (disambiguation Perseus (ˈpɝsiːəs or /-sjuːs/ is a northern Constellation, named after the Greek Camelopardalis ( from Ancient Greek καμηλοπάρδαλις - kamēlopardalis Giraffe) is the name of a large but faint northern In Astronomy, declination (abbrev dec or δ) is one of the two coordinates of the Equatorial coordinate system, the other being either Because the orbit of Eris is highly inclined, it only passes through a few constellations of the traditional Zodiac. Zodiac denotes an annual cycle of twelve stations along the Ecliptic, the apparent path of the sun across the heavens through the Constellations that divide the ecliptic

Size, mass, and density

The diameter of Eris has been measured to be 2397 km, give or take 100 km, using images from the Hubble Space Telescope. Geometry, a diameter of a Circle is any straight Line segment that passes through the center of the circle and whose Endpoints are on the The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into ^[27] (The brightness of an object depends both on its size and the amount of light it reflects (its albedo)). The albedo of an object is the extent to which it diffusely reflects light from the sun At a distance of 97 AU, an object with a radius of 3000 km would have an angular size of 40 milliarcseconds,^[6] which is directly measurable with the HST; although resolving such small objects is at the very limit of Hubble's capabilities,^[c] sophisticated image processing techniques such as deconvolution can be used to measure such angular sizes fairly accurately. The angular diameter of an object as seen from a given position is the "visual diameter" of the object measured as an angle A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60 of one degree. In Mathematics, deconvolution is an algorithm-based process used to reverse the effects of Convolution on recorded data ^[d])

Eris compared to Pluto, (136472) 2005 FY₉, (136108) 2003 EL₆₁, Sedna, Orcus, Quaoar, Varuna, and Earth.

This makes Eris only 0-8% larger than Pluto, which is about 2306 km across. It also indicates an albedo of 0. 86, higher than any other large body in the Solar system other than Enceladus. TemplateInfobox Planet.--> This article is about the moon of It is speculated that the high albedo is due to the surface ices being replenished due to temperature fluctuations as Eris' eccentric orbit takes it closer and farther from the Sun. The Sun (Sol is the Star at the center of the Solar System. ^[28]

In 2007, a series of observations of the largest trans-Neptunian objects with the Spitzer Space Telescope gave an estimate of Eris's diameter of 2600⁺⁴⁰⁰₋₂₀₀km. The Spitzer Space Telescope (formerly the Space Infrared Telescope Facility, SIRTF) is an Infrared Space observatory. ^[4] The Spitzer and Hubble estimates overlap in the range of 2400-2500 km, 4-8% larger than Pluto.

The mass of Eris can be calculated with much greater precision. Based on the currently accepted value for Dysnomia's period, 15. Dysnomia (,, or as in Greek Δυσνομία officially (136199 Eris I Dysnomia, is the only known moon of the Dwarf planet Eris 774 days,^[29][5] Eris is 27 percent more massive than Pluto.

Thermal measurement

Previous observations of the thermal emission of Eris at a wavelength of 1. 2 mm, where the object's brightness depends only on temperature and surface area, indicated a diameter of 3000⁺²⁷⁰₋₁₀₀ km, about a third larger than Pluto. ^[30] If the object rotates quickly, resulting in a more even heat distribution and a temperature of 23 to 24 kelvins (-250 to -249 degrees Celsius), a likely diameter would be in the higher portion of the range (best fit 3090 km); if it rotates slowly, the visible surface would be warmer (about 27 K, or -246 degrees Celsius) and a likely diameter would be in the smaller end of the range (best fit 2860 km). The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic The 2860 km figure implies a Pluto-like albedo of 60%, consistent with its Pluto-like spectral signature.

The apparent inconsistency of the HST PSF results (2400 ± 100 km) with the above IRAM results (3000 ± 370 km) will certainly be studied at more length. The Institut de radioastronomie millimétrique (IRAM operates two observatories for Radio astronomy at millimeter wavelengths, which are open to the international Brown explains it by a slightly lower absolute magnitude than the one assumed by Bertoldi (−1. Education Brown is a Huntsville Alabama native and graduated from Virgil Grissom High School in 1983 In Astronomy, absolute magnitude (also known as absolute visual magnitude) is the Apparent magnitude an object would have if it were at a standard 12 ± 0. 01 versus −1. 16 ± 0. 1, resulting by itself in almost 100 km difference in diameter). Assuming further the highest diameter (2500 km) and pole-on position of the object^[e] the difference between the results would appear consistent with 1. 1-σ error margin. In Probability and Statistics, the standard deviation is a measure of the dispersion of a collection of values

Another possible explanation for the IRAM results is offered by the Max-Planck-Institut für Radioastronomie. The Max Planck Institute for Radio Astronomy is located in Bonn, Germany. The ratio between the bolometric albedo (representing the total reflected energy and used in the thermal method) and the geometric albedo (representing the reflection in some visual wavelength and used to calculate the diameter from HST pictures) is not known with high precision and depends on many factors. In Astronomy, absolute magnitude (also known as absolute visual magnitude) is the Apparent magnitude an object would have if it were at a standard The albedo of an object is the extent to which it diffusely reflects light from the sun By itself, this uncertainty could bridge the gap between the two measures. ^[30]

Surface and atmosphere

The infrared spectrum of Eris, compared to that of Pluto, shows the marked similarities between the two bodies. Arrows denote methane absorption lines. Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas.

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. Astronomical spectroscopy is the technique of Spectroscopy used in Astronomy. The Gemini Observatory is an astronomical observatory consisting of two 8-metre Telescopes at different sites The State of Hawaii ( or həˈwaɪʔiː Hawaiian: Mokuāina o Hawaii) is a state in the United States located on an Archipelago in the Events 41 - After a night of negotiation Claudius is accepted as Roman Emperor by the Senate Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. Infrared light from the object revealed the presence of methane ice, indicating that the surface may be similar to that of Pluto, which at the time was the only TNO known to have surface methane, and of Neptune's moon Triton, which also has methane on its surface. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. A trans-Neptunian object (TNO is any object in the Solar system that Orbits the sun at a greater distance on average than Neptune. TemplateInfobox Planet.--> Triton (ˈtraɪtən, or as in Greek ^[31]

Due to its distant eccentric orbit, Eridian surface temperatures are estimated to vary between about 30 and 56 kelvins (−243 and −217 degrees Celsius). ^[9]

Unlike the somewhat reddish Pluto and Triton, however, Eris appears almost grey. ^[9] Pluto's reddish colour is believed 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. Tholin (after the Greek word for muddy is a Heteropolymer formed by solar Ultraviolet irradiation of simple Organic compounds such as Methane The albedo of an object is the extent to which it diffusely reflects light from the sun In contrast, Eris is far enough away from the Sun that methane can condense onto its surface even where the albedo is low. The Sun (Sol is the Star at the center of the Solar System. Condensation is the change of the physical state of aggregation (or simply state of matter from gaseous phase into liquid phase The condensation of methane uniformly over the surface reduces any albedo contrasts and would cover up any deposits of red tholins. ^[32]

Even though Eris can be up to three times further from the Sun than Pluto, it approaches close enough that some of the ices on the surface might warm enough to sublimate. Sublimation of an element or compound is a transition from the Solid to Gas phase with no intermediate liquid stage Methane is highly volatile and its presence shows either that Eris has always resided in the distant reaches of the solar system where it is cold enough for methane ice to persist, or that it has an internal source of methane to replenish gas that escapes from its atmosphere. Volatility in the context of Chemistry, Physics and Thermodynamics is a measure of the tendency of a substance to Vaporize. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " This contrasts with observations of another recently-discovered TNO, 2003 EL₆₁, which reveal the presence of water ice but not methane. Water is a common Chemical substance that is essential for the survival of all known forms of Life. ^[33]

Moon

Artist impression of Eris and Dysnomia. Eris is the main object, Dysnomia the small grey disk just above it. The blurred object top-left is the Sun.

Main article: Dysnomia (moon)

In 2005 the adaptive optics team at the Keck telescopes in Hawaii carried out observations of the four brightest TNOs (Pluto, 2005 FY₉, 2003 EL₆₁, and Eris), using the newly commissioned laser guide star adaptive optics system. Dysnomia (,, or as in Greek Δυσνομία officially (136199 Eris I Dysnomia, is the only known moon of the Dwarf planet Eris Adaptive optics (AO is a Technology used to improve the performance of optical systems by reducing the effects of rapidly changing optical distortion The W M Keck Observatory is a two-telescope Astronomical observatory at the 4145 meter (13600 ft summit of Mauna Kea in Hawai'i. The State of Hawaii ( or həˈwaɪʔiː Hawaiian: Mokuāina o Hawaii) is a state in the United States located on an Archipelago in the A trans-Neptunian object (TNO is any object in the Solar system that Orbits the sun at a greater distance on average than Neptune. Laser guide stars are a form of artificial star created for use in Astronomical Adaptive optics imaging ^[34] Images taken on September 10 revealed a moon in orbit around Eris. Events 506 - The Bishops of Visigothic Gaul meet in the Council of Agde. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. 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. Gabrielle is a Fictional character in Xena Warrior Princess, played by Renée O'Connor. When Eris received its official name from the IAU, the moon received the name Dysnomia, after the Greek demon of lawlessness who was Eris' daughter. Dysnomia (,, or as in Greek Δυσνομία officially (136199 Eris I Dysnomia, is the only known moon of the Dwarf planet Eris Dysnomia (Δυσνομία imagined by Hesiod among the daughters of "abhorred Eris " ("Strife" is the daemon of "lawlessness"

See also

• Astronomical naming conventions
• Cleared the neighbourhood
• Hypothetical trans-Neptunian planets
• International Astronomical Union
• Planet X

Notes

References

External links

• Michael Brown's webpage about 2003 UB₃₁₃
• Brown's webpage about 2003 UB₃₁₃'s satellite
• compiled list of data
• MPEC listing for 2003 UB₃₁₃
• Java 3D orbit visualization
• Spaceflight Now article about 2003 UB₃₁₃, 2003 EL₆₁, and 2005 FY₉
• Slacker Astronomy Interview With Co-Discoverer Trujillo
• Trans-Neptunian Object 2003 UB₃₁₃ — IAU statement regarding the planetary status of 2003 UB₃₁₃
• Simulation of 2003 UB₃₁₃'s orbit — 2003 UB₃₁₃ is in a 17:5 resonance with Neptune
• Keck observatory page about the discovery of 2003 UB₃₁₃'s moon
• Caltech Press Release, 7/29/2005 "Planetary Scientists Discover Tenth Planet".
• Press release on the Spitzer Space Telescope trying to image 2003 UB₃₁₃ again

Observatories involved

• Keck Observatory, Hawaiʻi, US
• Palomar
• Gemini
• IRAM (Institut de Radio Astronomie Millimétrique (Institute for Millimetric Radio Astronomy)): French-German (Max-Planck Institut fur Radioastronomy, Bonn) and Spanish (where the 30 m telescope is situated) collaborative programme.
• HST