Size, density, albedo and atmosphere limit of dwarf planet Eris from a stellar occultation

We report the observation of a multi-chord stellar occultation by the dwarf planet (136199) Eris. The event was observed on November 6, 2010 UT, from two sites in Chile. Our observation is consistent with a spherical Eris with radius RE=1163±6 km, density =2.52±0.05 g cm-3, and visible geometric albedo pV=0.96+0.09 -0.04. Besides being remarkably similar in size to Pluto, Eris appears as one of the intrinsically brightest objects of the solar system, with a density suggesting a mainly rocky interior. Upper limits of about 1 nbar are derived for the surface pressure of possible nitrogen, argon or methane atmospheres of the dwarf planet.