The Size of Pluto's Atmosphere As Revealed by the 2006 June 12 Occultation

Abstract

Observations of the 2006 June 12 occultation of P384.2 (McDonald & Elliot, AJ 120, 1599; aka UCAC2-26039859) were attempted at five sites by the MIT-Williams occultation group. Four were successful: the 0.8-m telescope at the Star Castle Observatory in Black Springs, the 1 m at the Mt. Canopus Observatory in Hobart, the 1.8 m at Mt. Stromlo, and the 2.3-m ANU telescope at Siding Spring. The data were recorded with our Portable Occultation, Eclipse, and Transit Systems (POETS; Souza et al., in preparation). These telescopes were located on both sides of the centerline and yielded light curves of good to excellent signal-to-noise ratio, in spite of Pluto being located 15º deg from a 15.7 day-old-moon. Above the 0.50 stellar flux level (and somewhat below it), Pluto's atmosphere is well described by an isothermal model, having the same scale height (within the errors) at all of our stations. Thus the 0.50 flux level provides a well-defined, consistent fiducial for measuring the radius of Pluto's atmosphere. All eight occultation timings (immersion and emersion at each station) were used in a least-squares fit for the radius. Results will be compared with Pluto's atmospheric size in 2002 (Person et al., Icarus, submitted), which had expanded significantly from that reported in 1988 (Elliot et al., Nature 424, 165). Pluto's atmospheric structure as derived from these data is discussed in the abstract by Gulbis et al. and the use of these data to probe for unknown satellites and debris in the Pluto-Charon system is discussed in the abstract by Pasachoff et al. Show more