- This article is about the Dwarf Planet named Eris. For the classical goddess, see Eris (mythology). For any other use, see Eris (disambiguation).
|Date of discovery||October 21, 2003|
|Name of discoverer||Michael E. Brown|
|Name origin||Greek goddess of discord|
|Order from primary||12|
|Semi-major axis||67.732 AU|
|Titius-Bode prediction||154 AU|
|Sidereal year||557.4 a|
|Avg. orbital speed||3.436 km/s|
|Inclination||44.1595° to the ecliptic|
|Sidereal day||8 h|
|Mass||1.66 * 1022 kg|
|Mean radius||1,300 km|
|Surface gravity||0.6554 m/s²|
|Escape speed||1.305 km/s|
|Surface area||21,237,166 km²|
|Minimum temperature||30 K|
|Mean temperature||42.5 K|
|Maximum temperature||55 K|
|Number of moons||1|
|Color||white to light gray|
Discovery, Naming, and Debate
Eris was first photographed on October 21, 2003, but was at first too slow-moving for the Palomar Observatory image-analytic software to detect. Later, Michael E. Brown, Chad Trujillo, and David Rabinowitz ordered re-analysis of the images with greater sensitivity. They soon realized that the images depicted a new object, and announced their findings on January 5, 2005.
The initial name for the new object was Xena, the title character in an American television action-adventure dramatic series, and also a name beginning with X, in keeping with the suspicion that this object was the long-sought "Planet X." The object also had a satellite, which the discoverers tentatively named Gabrielle, after the supporting character in that dramatic series.
The announcement of Eris' discovery on July 29, 2005 presented the International Astronomical Union with an embarrassing problem. Other observations, specifically of the period and orbital characteristics of the satellite, had already suggested that 2003 UB313 might be more massive even than Pluto, then considered the ninth planet in the solar system. Because planets and Kuiper-Belt objects have different naming conventions, and because scattered disk objects had no naming convention at the time, the names for the new primary and satellite remained unofficial.
Finally the International Astronomical Union declared that Pluto and 2003 UB313 were not planets, but belonged to a new category called dwarf planets. Then on September 6, 2006, Mike Brown and his team recognized that the name "Xena" was inappropriate for 2003 UB313 and suggested to the IAU that they name it Eris, after the Greek goddess of discord and strife. They also suggested that the IAU name the satellite Dysnomia, for the Greek goddess of lawlessness and daughter of Eris. Four days later, the IAU officially named the primary Eris and named its satellite Dysnomia.
At 67.7 AU from the Sun, it is the most distant object yet discovered that has the Sun for a primary. At aphelion, it is far beyond the Kuiper belt and in what is known as the scattered disk of the solar system. Because Eris is so distant from Earth (currently near aphelion and hence three times more distant than is Pluto as of 2008), it has a very long sidereal year of 557 Julian years. Its synodic year is very nearly the same as an Earth year.
Surface and atmospherePluto, which is known to have a layer of methane on its surface. From this, the discovery team concludes that Eris is surfaced with solid frozen methane, with rock and water ice beneath.
Yet Eris is the second most reflective body in the entire solar system, reflecting about 86% of the incident sunlight. Eris is also uniformly white on its surface, whereas Pluto is a mottled brown. The discoverers believe that this is due entirely to Eris' present far-flung position (near aphelion), and point out that Eris' orbit is the most eccentric orbit of any satellite of the Sun, except for comets.
Implications for Other Trans-Neptunian Objects
Brown et al. noted in 2005 that Eris, Dysnomia's primary, is one of three of the four brightest Kuiper belt objects that have satellites. (The other two are Pluto and 2003 EL61.) The fourth, 2005 FY9, has no satellite that Earth-based telescopes can presently detect. Most Kuiper belt objects do not have satellites, and that three of the four brightest should have satellites suggests that their origins were significantly different from those of other Kuiper belt objects.
Problem for uniformitarian theories
Brown states that the near-circular orbit of Dysnomia about Eris actually is consistent with Dysnomia's origin as the result of a collision between Eris and another object. But no astronomer has ever explained how such a collision would leave an object in a nearly circular orbit about its primary.
Observation and exploration
The Hubble Space Telescope and the Keck Observatory are the first two telescopes to observe the Eridian system. No deep-space missions are planned.
- "Discovery Circumstances: Numbered Minor Planets." International Astronomical Union, Minor Planet Center, May 1, 2007. Accessed May 15, 2008.
- "Gazetteer of Planetary Nomenclature: Planetary Body Names and Discoverers." US Geological Survey, Jennifer Blue, ed. March 31, 2008. Accessed April 17, 2008.
- Brown, M.E., Van Dam, M. A., Bouchez, A. H., Le Mignant, D., et al. "Satellites of the Largest Kuiper Belt Objects." Astrophys. J. Lett. 639(L43), October 3, 2005. <arXiv:astro-ph/0510029.> Accessed May 15, 2008.
- Johnston, William Robert. "Entry for 136199 Eris and Dysnomia." Johnston Archive, August 21, 2007. Accessed May 15, 2008.
- Brown, Michael E., and Schaller, Emily L. "The Mass of Dwarf Planet Eris." Science, 316(5831):1585, June 15, 2007. <doi:10.1126/science.1139415> Accessed May 15, 2008.
- Reitan, Kari. "Astronomers Measure Mass of Largest Dwarf Planet." Space Telescope Science Institute, National Aeronautics and Space Administration, June 14, 2007. Accessed January 21, 2008.
- "Comment on the recent Hubble Space Telescope size measurement of 2003 UB313 by Brown et al." Max Planck Institut für Radioastronomie, April 13, 2006. Accessed May 15, 2008.
- The character is supposed to be a princess from a tribe of warriors, either Argive or closely allied with them, in the days of the Mycenean civilization, and a contemporary of, and occasional rival to, Hercules. No historical warrant exists for the existence of such a person or even for a classical poem mentioning that name.
- Hamilton, Calvin J. "Entry for 'Eris'." Views of the Solar System, 2007. Accessed January 21, 2008.
- Ingham, Richard. "'Tenth planet' Xena bigger than Pluto." Agence France-Presse, quoted by Australian Broadcasting Corporation, February 2, 2006. Accessed May 15, 2008.
- Eris (2003 UB313) and Dysnomia. Accessed January 22, 2008.
- Tytell, David. "All Hail Eris and Dysnomia." Sky and Telescope, September 14, 2006. Accessed May 15, 2008.
- "IAU0602: the Final IAU Resolution on the Definition of 'Planet' Ready for Voting," International Astronomical Union, 2005. Accessed January 14, 2008.
- Brown, Mike. "The discovery of Eris, the largest known dwarf planet." California Institute of Technology. Accessed January 22, 2008.
- Dysnomia, meaning "lawlessness," is also a play on the name of the American actress who portrayed Xena, Lucy Lawless.
- IAU Circular No. 8747, International Astronomical Union, September 10, 2006. Accessed May 15, 2008.