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

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, R.; VIEIRA, R.; AGEORGES, N.; HAINAUT, O.; MARCO, O.; BEISKER, W.; HUMMEL, E.; FEINSTEIN, C.; LEVATO, H.; MAURY, A.; FRAPPA, E.; GAILLARD, B; LAVAYSIERE, M.; DI SORA, M.; MALLIA, F.; 18 AUTORES MáS

NATURE

Nature Publishing Group

Año: 2006 vol. 439 p. 52 - 54

0028-0836

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 600km for the satellite's radius, which was later refined to 601.5km (ref. 4). Here we report observations from a multi-station stellar occultation by Charon, which we use to derive a radius, RC = 603.6 +/- 1.4km (1ó), and a density of ñ = 1.71 +/- 0.08gcm-3. This occultation also provides upper limits of 110 and 15 (3ó) nanobar for an atmosphere around Charon, assuming respectively a pure nitrogen or pure methane atmosphere