Charon's size and an upper limit on its atmosphere from a stellar occultation
Charon's size and an upper limit on its atmosphere from a stellar occultation
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卡戎的大小和恒星掩星对其大气层的上限
DOI：
10.1038/nature04351
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发表时间：
2006
期刊：
影响因子：
64.8
通讯作者：
G. Tancredi
中科院分区：
文献类型：
--
作者：
B. Sicardy;A. Bellucci;E. Gendron;F. Lacombe;S. Lacour;J. Lecacheux;E. Lellouch;S. Renner;S. Pau;F. Roques;T. Widemann;F. Colas;F. Vachier;R. V. Martins;N. Ageorges;O. Hainaut;O. Marco;W. Beisker;E. Hummel;Carlos Feinstein;H. Levato;A. Maury;E. Frappa;B. Gaillard;M. Lavayssière;M. D. Sora;F. Mallia;G. Masi;R. Behrend;F. Carrier;O. Mousis;P. Rousselot;A. Alvarez;D. Lazzaro;C. Veiga;A. Andrei;M. Assafin;D. D. S. Neto;C. Jacques;E. Pimentel;D. Weaver;J. Lecampion;F. Doncel;T. Momiyama;G. Tancredi
冥王星及其卫星卡戎（Charon，1978 年发现；参考文献 1）似乎形成了一颗双行星，而不是分层的行星/卫星对。卡戎的大小约为冥王星的一半，质量约为冥王星的八分之一。冥王星和卡戎的精确半径仍然不确定，导致它们的密度存在很大的不确定性。尽管卡戎的恒星掩星原则上是测量其大小的有效方法，但这种情况很少见，因为卫星在天空上的对向不到 0.3 微弧度（0.06 角秒）。一次掩星（1980 年）得出卫星半径的下限为 600 公里，后来细化为 601.5 公里（参考文献 4）。在这里，我们报告了卡戎多站恒星掩星的观测结果，我们用它来推导半径 RC = 603.6 ± 1.4 km (1σ) 和密度 ρ = 1.71 ± 0.08 g cm-3。这种掩星还为卡戎周围的大气提供了 110 和 15 (3σ) 纳米巴的上限，分别假设为纯氮气或纯甲烷大气。
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, RC = 603.6 ± 1.4 km (1σ), and a density of ρ = 1.71 ± 0.08 g cm-3. This occultation also provides upper limits of 110 and 15 (3σ) nanobar for an atmosphere around Charon, assuming respectively a pure nitrogen or pure methane atmosphere.