Eris (dwarf planet)

( 136199 ) Eris is the most massive known dwarf planet in the solar system. Eris is one of the Plutoiden, a sub-class of dwarf planets that orbit the Sun beyond the orbit of Neptune.

The dwarf planet is named after Eris, the Greek goddess of discord and strife. After its discovery on July 29, 2005, NASA and many media referred to this object of the Kuiper belt with a diameter similar to Pluto first as a " tenth planet ". The International Astronomical Union ( IAU), however, adopted on 24 August 2006, a new planet definition, according to the Eris, just as Pluto had to be classified as a dwarf planet. The object was, accordingly, in September 2006 as a minor planet number 136,199th

Eris moving on a highly eccentric and inclined relative to the ecliptic orbit around the sun, from which it is currently about 98 AU ( 15 billion kilometers ) away. They counted because of their large eccentricity to the so-called " scattered " Kuiper belt objects. Another name is Scattered disk object (SDO ).


Eris was discovered by Mike Brown ( Caltech ), Chad Trujillo (Gemini Observatory ) and David Rabinowitz ( Yale University). The same astronomers succeeded previously been the discovery of the great Trans Neptune Quaoar, Sedna and Orcus. Eris was found on CCD images of the 1.2 -meter Schmidt telescope at Mount Palomar Observatory on 21 October 2003. Because it moves slowly, it was overlooked in the first processing of the images. Only with a new evaluation of the exposures the object was found on 5 January 2005 in the Kuiper Belt. After the three identified it on older recordings dating back to September 3, 1954; the path data are therefore now determined very safe.

At first she wanted to publish their find after further observations. But after it became known that everyone could query the orientation of one of the telescopes on a public website with which their discoverer Eris had observed, the researchers went on 29 July 2005 in advance to the public. Only 19 hours earlier, had made known their discovery of Haumea Spanish astronomers; the group led by Brown had the same object independently found by them in 2004, but published nothing about it until then. On the same day Brown's group split then with the discovery of Makemake; so that the public learned in a single day that three new large objects were discovered in the Kuiper Belt.


After its discovery, the provisional designation 2003 UB313 was awarded by the IAU for Eris. It follows the usual rules for naming asteroids and expresses only encodes from that Eris in the second half of October (U ) for the year was discovered in 2003, after the order of the 7827th object found ( B313 ). The working group of explorers called Eris, first internally and unofficially " Xena " and its moon " Gabrielle", after two role names from the television series Xena - Warrior Princess. This suggested itself, because in the series, many topics Greek and Roman mythology are treated and many other objects of the solar system also contribute mythological names. Gabrielle is in the series also Xena's companion, just as the moon is Trabant of the minor planets.

In September 2006, received 2003 UB313 then the minor planet number 136,199th This was followed by the award of the permanent name. Since the September 13, 2006 2003 UB313 now bears the name Eris, her moon the name Dysnomia.

In Greek mythology, Eris is the goddess of discord and strife, whose intrigue triggers the Trojan War. Her daughter, the demon of lawlessness is called Dysnomia. Both names give an indication of the bitter controversy that eventually led to the new definition of "planet" and the denial of the planetary status of Pluto after its discovery. Another reference is made to the originally chosen working name " Xena ". The film character Xena was played by the actress Lucy Lawless. Lawlessness is the English term for lawlessness, after the award of the name Dysnomia alludes.

The tenth planet?

The media called Eris, Quaoar and Sedna as well already, as a " tenth planet " ( → Trans Pluto). The discoverers and NASA considered it the same way. Such a classification was published, the experts believe plausible, because on the one hand Eris seemed even larger than Pluto to be, and on the other hand were for the planet status of the latter already features of the planet definition - bounds on the eccentricity as well as the condition that a planet has a greater mass than all other objects must have along in its orbit - have been ignored. But since the late 1990s, many astronomers tended to be no more counting Pluto itself to the planet; they called him instead as the hitherto largest trans-Neptunian object. The discovery of Eris sparked anew the debate, according to which characteristics celestial bodies are to count as planets.

The 26th General Assembly of the International Astronomical Union in August 2006 in Prague then adopted a new official definition for planets and dwarf planets. Thus, Eris, Pluto and Ceres are now as a dwarf planet. The status of Sedna and Quaoar is still unclear. At the same time we defined a sub- class of trans-Neptunian dwarf planets that should be initially called plutons. This designation was still in favor of the new name discarded Plutoiden to which you next Eris now also the namesake Pluto account.


To determine the size of an object from the apparent brightness, which is about 18.7 m at Eris, both its distance and its albedo must be known. Then can calculate its size; less albedo leads with the same apparent brightness to a larger value of the diameter.

Even with a maximum albedo of 1, so if they would reflect all the light would be Eris after Brown calculations at least the same size as Pluto. Since it was not found by the Spitzer Space Telescope, it said in the first messages, their diameter must be less than 3200 km. Meanwhile, it turned out that the telescope was not designed by an operator error on the object. According to Mike Brown led to the end of August 2005 announced new observations by the Spitzer Space Telescope. The measured data are currently being analyzed.

The first reliable measurement of the magnitude achieved in early 2005 radio astronomers from the Max Planck Institute for Radio Astronomy in Bonn. Using the IRAM radio telescope on Pico Veleta in southern Spain del they measured the thermal radiation of Eris. In combination with optical observations, the albedo at 0.60 ± 0.11 and from this the diameter was limited to 3000 ± 320 km.

The discovery team also received observing time on the Hubble Space Telescope. Although the device already comes with a angular diameter of an object of only 0.035 arcseconds to the limits of its performance, the team managed by Brown with special image processing techniques ( deconvolution ) to determine the size of Eris to 2400 ± 100 kilometers. Consequently, Eris was smaller than previous measurements would imply, about the same size as Pluto. Here the albedo of Eris was found to be 0.85 ± 0.07.

On 5 November 2010 the size of Eris in transit in front of a star as could never be determined exactly. Eris therefore has a diameter of 2326 ± 12 km, thus slightly more than Pluto, and has largely spherical shape.

Moon Dysnomia

Eris has a moon named Dysnomia, discovered on 10 September 2005 by the same team as Eris. Since the Moon has about the 500th part of the luminosity of Eris, the diameter should be around 100 kilometers. If the albedo of Dysnomia would be much smaller than that of Eris, the diameter may reach up to 250 kilometers. Dysnomia needed for one orbit around the dwarf planet just 16 days, their distance to it is about 37,000 kilometers.


An orbit around the sun takes about 560 a The railway is not uncommon for an object in the Kuiper Belt, highly eccentric ( eccentricity 0.44). So the perihelion of its orbit is only at 38 AU. They may temporarily the sun are closer than Pluto, its aphelion is 49 AU. Currently, Eris is near the aphelion of its orbit, about 98 AU from the sun. This corresponds to a distance of about 13.5 hours of light.

It is striking that the orbit of Eris is inclined at 44 ° to the ecliptic, which is unusual for a body of this size and probably delaying the discovery. Most search Kuiper Belt programs for Objects ( KBOs ) or other asteroids are limited to positions in the approximate vicinity of the ecliptic, because there the majority of the matter in the solar system is concentrated. Maybe Eris was directed by the gravitational influence of Neptune in this pathway.


Some sources speak of a composition of about 70 percent rock and 30 percent frozen water. But as long as neither mass nor diameters are precisely known, such information must be rather skeptical view. Spectroscopic observations at the Gemini Observatory in Hawaii have also pointed to the presence of frozen methane on the surface of Eris. It would thus be similar to that of Pluto; due to the small size presumable high albedo based likewise. This Eris shows more similarity with Pluto and its moon Charon as with the other KBOs. Since methane is highly volatile, the object can be also hardly penetrated deeper into his past in the inner solar system. The methane would otherwise be sublimated and would have dissipated. Furthermore, it could be detected on the surface of frozen nitrogen, with its concentration significantly altered by studies with the "Multiple Mirror Telescope" on Mount Hopkins in Arizona between 2005 and 2007.

Eris is large enough to hold similar to Pluto a very thin atmosphere of nitrogen, methane and carbon monoxide. This would periodically resublimation with increasing distance from the sun and thus the decrease of the surface temperature on the surface, then re- sublimate the rise in temperature again, and form an atmosphere again. Because Eris is currently staying very close to its aphelion, may be present currently no atmosphere.

It is estimated that the surface temperature of Eris to 30 K (about -242 ° C). It is thus again significantly lower than that of Pluto. This is primarily due to greater distance from the Sun; because of their (compared to geologically active planet like Earth ) small size and their formation at the outer edge of the solar system, they can have no appreciable internal energy sources. The tidal heating of the moon could slightly affect the temperature, the moon Dysnomia should have a sufficient mass for it.