Charon's size and an upper limit on its atmosphere from a stellar occultation

• Published in: Nature Vol. 439; no. 7072; pp. 52 - 54
• Main Authors: Behrend, R, Lecampion, J.-F, Feinstein, C, Gaillard, B, Lacour, S, Frappa, E, Alvarez-Candal, A, Pimentel, E, Veiga, C, Hummel, E, Doncel, F, Jacques, C, Lavayssière, M, Pau, S, Roques, F, Bellucci, A, Mousis, O, Marco, O, Carrier, F, Gendron, E, Mallia, F, Levato, H, Tancredi, G, Hainaut, O, Masi, G, Lecacheux, J, Vachier, F, Assafin, M, Lellouch, E, Martins, R. Vieira, Lazzaro, D, da Silva Neto, D. N, Ageorges, N, Di Sora, M, Weaver, D, Momiyama, T, Widemann, T, Lacombe, F, Colas, F, Renner, S, Rousselot, P, Sicardy, B, Maury, A, Beisker, W, Andrei, A. H
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 05.01.2006; Nature Publishing Group
• Subjects: Astronomy; Astrophysics; Atmosphere; Earth and Planetary Astrophysics; Earth, ocean, space; Exact sciences and technology; Mass, size; gravitational fields; rotation; orbits; Methane; Moons; Nitrogen; Physics; Planetary, asteroid, and satellite characteristics and properties; Planets; Planets, their satellites and rings. Asteroids; Pluto; Sciences of the Universe; Solar system; Bulk density; Methane; Occultations; Satellite atmospheres; Uncertainty; Pluto satellite; Charon; Diameter; Pluto planet
• ISSN: 0028-0836; 1476-4687; 1476-4679
• DOI: 10.1038/nature04351

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.