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Sicardy B Bellucci A Gendron E Lacombe F Lacour S Lecacheux J Lellouch E Renner S Pau S Roques F Widemann T Colas F Vachier F Martins RV Ageorges N Hainaut O Marco O Beisker W Hummel E Feinstein C Levato H Maury A Frappa E Gaillard B Lavayssière M Di Sora M Mallia F Masi G Behrend R Carrier F Mousis O Rousselot P Alvarez-Candal A Lazzaro D Veiga C Andrei AH Assafin M da Silva Neto DN Jacques C Pimentel E Weaver D Lecampion JF Doncel F Momiyama T Tancredi G 《Nature》2006,439(7072):52-54
Pluto and its satellite, Charon (discovered in 1978; ref. 1), appear to form a double planet, rather than a hierarchical planet/satellite couple. Charon is about half Pluto's size and about one-eighth its mass. The precise radii of Pluto and Charon have remained uncertain, leading to large uncertainties on their densities. Although stellar occultations by Charon are in principle a powerful way of measuring its size, they are rare, as the satellite subtends less than 0.3 microradians (0.06 arcsec) on the sky. One occultation (in 1980) yielded a lower limit of 600 km for the satellite's radius, which was later refined to 601.5 km (ref. 4). Here we report observations from a multi-station stellar occultation by Charon, which we use to derive a radius, R(C) = 603.6 +/- 1.4 km (1sigma), and a density of rho = 1.71 +/- 0.08 g cm(-3). This occultation also provides upper limits of 110 and 15 (3sigma) nanobar for an atmosphere around Charon, assuming respectively a pure nitrogen or pure methane atmosphere. 相似文献
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