Pluto and Eris are icy dwarf planets with nearly identical sizes, comparable densities and similar surface compositions as revealed by spectroscopic studies1,2. Pluto possesses an atmosphere whereas Eris does not; the difference probably arises from their differing distances from the Sun, and explains their different albedos3. Makemake is another icy dwarf planet with a spectrum similar to Eris and Pluto4, and is currently at a distance to the Sun intermediate between the two. Although Makemake’s size (1,420 ± 60 km) and albedo are roughly known5,6, there has been no constraint on its density and there were expectations that it could have a Pluto-like atmosphere4,7,8. Here we report the results from a stellar occultation by Makemake on 2011 April 23. Our preferred solution that fits the occultation chords corresponds to a body with projected axes of 1,430 ± 9 km (1σ) and 1,502 ± 45 km, implying a V-band geometric albedo pV = 0.77 ± 0.03. This albedo is larger than that of Pluto, but smaller than that of Eris. The disappearances and reappearances of the star were abrupt, showing that Makemake has no global Pluto-like atmosphere at an upper limit of 4–12 nanobar (1σ) for the surface pressure, although a localized atmosphere is possible. A density of 1.7 ± 0.3 g cm−3 is inferred from the data.
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These results were based partially on observations made with European Southern Observatory Telescopes at the La Silla and Paranal Observatories under programme 287C-5013. J.L.O. acknowledges funding from Spanish and Andalusian grants and the European Regional Development Fund (FEDER). B.S. acknowledges support from French National Research Agency (ANR) grant ‘Beyond Neptune’, and from the Institut Universitaire de France. E.U.-S. acknowledges the support from the Chilean National Commission for Scientific and Technical Research (Gemini-CONICYT funds), and from the North Catholic University of Chile Vicerectorate of Research and Technology Development (UCN-VRIDT). 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 grants by the Brazilian National Council for the Development of Science and Technology (CNPq), and the Foundation for Research Support of the State of Rio de Janeiro (FAPERJ). P.S.-S. acknowledges financial support by the Centre National de la Recherche Scientifique (CNRS). R.G.-H. acknowledges partial financial support by the Argentinian National Scientific and Technical Research Council (CONICET). F.B.-R. acknowledges the support of the French-Brazilian Doctoral College Coordination of Improvement of Graduated Personnel programme (CDFB/CAPES). A.A.-C. acknowledges support from the Marie Curie Actions of the European Commission (FP7-COFUND). S.P.L., V.S.D. and T.R.M. acknowledge funding for ULTRACAM from the UK Science and Technology Facilities Council. R.D. acknowledges support from Spanish Ministry of Economics and Competitiveness through a Ramón y Cajal contract.
This file contains Supplementary Text and Data 1-8, Supplementary Figures 1-7, Supplementary Table 1 and additional references.