Stellar Systems Group

Sicardy, B.; Ortiz, J. L.; Assafin, M.; Jehin, E.; Maury, A.; Lellouch, E.; Hutton, R. Gil; Braga-Ribas, F.; Colas, F.; Hestroffer, D.; Lecacheux, J.; Roques, F.; Santos-Sanz, P.; Widemann, T.; Morales, N.; Duffard, R.; Thirouin, A.; Castro-Tirado, A. J.; Jelínek, M.; Kubánek, P.; Sota, A.; Sánchez-Ramírez, R.; Andrei, A. H.; Camargo, J. I. B.; da Silva Neto, D. N.; Gomes, A. Ramos; Martins, R. Vieira; Gillon, M.; Manfroid, J.; Tozzi, G. P.; Harlingten, C.; Saravia, S.; Behrend, R.; Mottola, S.; Melendo, E. García; Peris, V.; Fabregat, J.; Madiedo, J. M.; Cuesta, L.; Eibe, M. T.; Ullán, A.; Organero, F.; Pastor, S.; de Los Reyes, J. A.; Pedraz, S.; Castro, A.; de La Cueva, I.; Muler, G.; Steele, I. A.; Cebrián, M.; Montañés-Rodríguez, P.; Oscoz, A.; Weaver, D.; Jacques, C.; Corradi, W. J. B.; Santos, F. P.; Reis, W.; Milone, A.; Emilio, M.; Gutiérrez, L.; Vázquez, R.; Hernández-Toledo, H. 
Nature, Volume 478, Issue 7370, pp. 493-496 (2011).
10/2011

ABSTRACT

The dwarf planet Eris is a trans-Neptunian object with an orbital eccentricity of 0.44, an inclination of 44 degrees and a surface composition very similar to that of Pluto. It resides at present at 95.7 astronomical units (1AU is the Earth-Sun distance) from Earth, near its aphelion and more than three times farther than Pluto. Owing to this great distance, measuring its size or detecting a putative atmosphere is difficult. Here we report the observation of a multi-chord stellar occultation by Eris on 6 November 2010 UT. The event is consistent with a spherical shape for Eris, with radius 1,163+/-6kilometres, density 2.52+/-0.05 grams per cm³ and a high visible geometric albedo, . No nitrogen, argon or methane atmospheres are detected with surface pressure larger than ~1nanobar, about 10,000 times more tenuous than Pluto's present atmosphere. As Pluto's radius is estimated to be between 1,150 and 1,200 kilometres, Eris appears as a Pluto twin, with a bright surface possibly caused by a collapsed atmosphere, owing to its cold environment. We anticipate that this atmosphere may periodically sublimate as Eris approaches its perihelion, at 37.8 astronomical units from the Sun.