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 Pluto1. It resides at present at 95.7 astronomical units (1 au 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 ± 6 kilometres, 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 ∼1 nanobar, about 10,000 times more tenuous than Pluto's present atmosphere2,3,4,5. As Pluto's radius is estimated3,4,5,6,7,8 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.
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We thank W. M. Owen and S. Preston for providing astrometric updates on the occulted star just before the observations, and I. Belskaya and M. E. Brown for discussions when writing the paper. We acknowledge support from the French grant ‘Beyond Neptune’ and from the Institut Universitaire de France. J.L.O., A.J.C.-T., L.C. and M.T.E. acknowledge funding from Spanish AYA grants and FEDER funds. TRAPPIST is a project funded by the Belgian Fund for Scientific Research (FRS-FNRS) with the participation of the Swiss National Science Foundation (SNF). J.I.B.C. acknowledges CNPq and FAPERJ grants. F.B.-R. acknowledges the support of CDFB/CAPES, Brazil. W.J.B.C., W.R. and F.P.S. thank the Brazilian Agency FAPEMIG.
The authors declare no competing financial interests.
This file contains Supplementary Text and Data 1-7, Supplementary Figures 1- 5 with legends, Supplementary Tables 1-5 and additional references. This file was replaced on 20 December to reinstate the type missing from the top of page 5. (PDF 489 kb)
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Sicardy, B., Ortiz, J., Assafin, M. et al. A Pluto-like radius and a high albedo for the dwarf planet Eris from an occultation. Nature 478, 493–496 (2011). https://doi.org/10.1038/nature10550
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