Dysnomia (formally (136199) Eris I Dysnomia) is the only known moon of the dwarf planet Eris and likely the second-largest known moon of a dwarf planet, after Pluto I Charon. It was discovered in 2005 by Mike Brown and the laser guide star adaptive optics team at the W. M. Keck Observatory, and carried the provisional designation of S/2005 (2003 UB313) 1 until officially named Dysnomia (from the Ancient Greek word Δυσνομία meaning anarchy/lawlessness) after the daughter of the Greek goddess Eris.

Dysnomia has an estimated diameter of 700±115 km (25% to 35% of Eris's diameter), and is among the dozen or so largest objects in the trans-Neptunian region.

 

Note:   The above text is excerpted from the Wikipedia article Dysnomia (moon), which has been released under the GNU Free Documentation License.