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{{Planet|image=Eris and Dysnomia.jpg
{{Planet|image=Eris and Dysnomia.jpg
|date=September 10, 2005
|discname=Michael E. Brown<ref name=usgs>"[http://planetarynames.wr.usgs.gov/append7.html Gazetteer of Planetary Nomenclature: Planetary Body Names and Discoverers]." US Geological Survey, Jennifer Blue, ed. March 31, 2008. Accessed April 17, 2008.</ref><ref name=Brown2>Brown, M.E., Van Dam, M. A., Bouchez, A. H., Le Mignant, D., ''et al''. "[http://arxiv.org/pdf/astro-ph/0510029 Satellites of the Largest Kuiper Belt Objects]." ''Astrophys. J. Lett.'' 639(L43), October 3, 2005. <arXiv:astro-ph/0510029.> Accessed May 15, 2008.</ref>
|origname=Greek goddess of lawlessness, daughter of Eris.<ref name=usgs/>
|primary=Eris
|primary=Eris
|periapsis=36,818 km
|order=1
|apoapsis=37,922 km
|periapsis=36,864 km<ref name=calc>Calculated</ref>
|semimajor=37,370 km
|apoapsis=37,836 km<ref name=calc/>
|semimajor=37,350 km<ref name=Brown1>Brown, Michael E., and Schaller, Emily L. "[http://www.sciencemag.org/cgi/content/abstract/316/5831/1585 The Mass of Dwarf Planet Eris]." ''Science'', 316(5831):1585, June 15, 2007. <doi:10.1126/science.1139415> Accessed May 15, 2008.</ref>
|eccentricity=0.013
|eccentricity=0.013
|sidereal=15.774 da
|sidereal=15.774 da<ref name=Brown1/>
|inclination=142.3°
|inclination=142.3°
|equatorradius =175 km
|equatorradius =175 km
}}'''Dysnomia''' is the only (so far) known [[moon]] of the [[dwarf planet]] [[Eris]]. It is named for the Greek goddess of lawlessness, daughter of Eris, goddess of discord and strife.
|image2=ErisDysnomiaConcept.jpg
}}'''Dysnomia''', or '''Eris I''', or '''S/2005 (2003 UB<sub>313</sub>) 1''', is the only (so far) known [[moon]] of the [[dwarf planet]] [[Eris]].
== Discovery ==
Astronomers Michael E. Brown at the California Institute of Technology, and [[discoverer::Marcos van Dam]], [[discoverer::Antonin Bouchez]], and [[discoverer::David Le Mignant]] of the William M. Keck Observatory in [[Hawaii]], are credited with the discovery of this object. The Keck team used their new Laser Guide Star Adaptive Optics system to examine more closely the newly discovered [[Kuiper belt]] object originally named 2003 UB<sub>313</sub> and then given the tentative name Xena.<ref name=Zabarenko>Zabarenko, Deborah. "[http://www.abc.net.au/science/news/stories/s1473136.htm Planet Xena has moon called Gabrielle]." Reuters, quoted by Australian Broadcasting Corporation, October 32, 2005. Accessed May 15, 2008.</ref> (Xena was the title character in an [[United States|American]] [[television]] action-adventure dramatic series,<ref>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.</ref> and also is a name beginning with X, in keeping with the suspicion that this object was the long-sought "Planet X.") Close examination of a faint object near the larger object clearly showed that this object was in motion and was not a [[star]].<ref name=VanDam>Van Dam, Marcos. [http://www2.keck.hawaii.edu/optics/staff/mvandam/gabrielle Discovery of Dysnomia]. William Keck Observatory. Accessed January 22, 2008.</ref><ref name=Brown3>[http://web.gps.caltech.edu/~mbrown/planetlila/moon/ The moon of the 10th planet]. California Institute of Technology. Accessed January 22, 2008.</ref>
== Naming ==
The initial name chosen for this object was Gabrielle, after the supporting role in the above-mentioned dramatic series. However, the status of object 2003 UB<sub>313</sub> (the primary) was the subject of debate, given that other observations<ref name=Ingham>Ingham, Richard. "[http://www.abc.net.au/science/news/stories/s1560563.htm 'Tenth planet' Xena bigger than Pluto]." Agence France-Presse, quoted by Australian Broadcasting Corporation, February 2, 2006. Accessed May 15, 2008.</ref><ref name=solstation>[http://www.solstation.com/stars/UB313.htm Eris (2003 UB<sub>313</sub>) and Dysnomia]. Accessed January 22, 2008.</ref> had already suggested that 2003 UB<sub>313</sub> 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 [[scatter disk]] objects had ''no'' naming convention at the time, the names for these two objects remained unofficial.<ref name=Tytell>Tytell, David. "[http://www.skyandtelescope.com/news/home/3916126.html All Hail Eris and Dysnomia]." ''Sky and Telescope'', September 14, 2006. Accessed May 15, 2008.</ref>
Finally the [[International Astronomical Union]] declared<ref>"[http://www.iau.org/iau0602.423.0.html IAU0602: the Final IAU Resolution on the Definition of 'Planet' Ready for Voting]," ''International Astronomical Union'', 2005. Accessed January 14, 2008.</ref> that Pluto and 2003 UB<sub>313</sub> were not planets, but belonged to a new category called [[dwarf planet]]s. Then on September 6, 2006, Mike Brown and his team<ref name=Brown4>Brown, Mike. "[http://www.gps.caltech.edu/%7Embrown/planetlila/index.html The discovery of Eris, the largest known dwarf planet]." California Institute of Technology. Accessed January 22, 2008.</ref> recognized that the name "Xena" was inappropriate for 2003 UB<sub>313</sub> 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.<ref>Dysnomia, meaning "lawlessness," is also a play on the name of the American actress who portrayed Xena, Lucy Lawless.</ref> Four days later, the IAU oficially named the primary Eris and named its satellite Dysnomia.<ref name=IAU1>[http://cfa-www.harvard.edu/iau/special/08747.pdf IAU Circular No. 8747], International Astronomical Union, September 10, 2006. Accessed May 15, 2008.</ref><ref>Brown</ref>
== Orbital characteristics ==
Dysnomia orbits Eris in a nearly circular orbit with a sidereal period of 15.774 days and a semi-major axis of 37,350 km. From these properties, Brown and Schaller were able to calculate Eris' mass.<ref name=Brown1/>
== 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 EL<sub>61</sub>.) The fourth, 2005 FY<sub>9</sub>, 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<ref name=Brown1/> 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.
== References ==
== References ==
{{reflist|2}}
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