Surface composition of the largest dwarf planet 136199 Eris (2003 UB)

¹ ESO, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19, Chile e-mail: cdumas@eso.org
² LESIA, Observatoire de Paris, 92195 Meudon Principal Cedex, France e-mail: frederic.merlin@obspm.fr

Received: 31 October 2006
Accepted: 1 June 2007

Abstract

Aims.The surface composition of the largest TNO, the dwarf planet 136199 Eris, is studied and compared to Pluto's.

Methods.High signal-to-noise visible and near-infrared reflectance spectra were obtained at the TNG and ESO-VLT observatories. The nature and properties of the compounds present on the surface of Eris are investigated by applying Hapke and Shkuratov radiative transfer models to our spectra.

Results.The surface of Eris can be modeled using two areas of distinct composition: about 50% appears to be covered with pure methane ice, while the rest of its surface would be made of an intimate mixture of methane, nitrogen and water ices, and ice tholin. The use of nitrogen in our model is shown to improve significantly the data fit, in particular for high surface albedo values. The icy grains are found to be large, from sub-mm to a few tens of mm in size.