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M. J. Person, J. L. Elliot, K. B. Clancy, S. D. Kern, C. V. Salyk (MIT), D. J. Tholen (U. of Hawaii), J. M. Pasachoff, B. A. Babcock, S. P. Souza, D. R. Ticehurst (Williams College), D. Hall, L. C. Roberts Jr. (Boeing), A. S. Bosh (BU & Lowell), M. W. Buie, E. W. Dunham, C. B. Olkin, B. Taylor (Lowell), S. E. Levine (USNO), S. S. Eikenberry, D.-S. Moon (Cornell), D. J. Osip (LCO)
The stellar occultation by Pluto of the 15th magnitude star designated P131.1 (McDonald and Elliot, AJ, 119, 1999) on 2002 August 21 (UT) provided the first significant chance to compare Pluto’s atmospheric structure to that determined from the 1988 occultation of P8 (Millis, et al., Icarus, 105, 282). The P131.1 occultation was observed from several stations in Hawaii and the western United States (Elliot et al., Nature, in press, 2003). Numerous occultation chords were obtained enabling us to examine Pluto’s atmospheric figure. The light curves from the observations were analyzed together in the occultation coordinate system of Elliot et al., (AJ, 106, 2544). The Mauna Kea and Lick datasets straddle the center of Pluto's figure, providing strong constraints on model fits to cross sections of the atmospheric shape.
In 1988, Millis (et al., Icarus, 105, 282) did not report any deviation from sphericity in Pluto's atmospheric figure. From the 2002 data, Pluto’s isobars at the radii probed by the occultation (~1250 km) appear to be distorted from a circular cross-section. Least-squares fits to this cross-section by elliptical models reveal ellipticities in the range 0.05-0.08 although the shape may be more complex than ellipsoidal. The orientation of the distortion appears uncorrelated with Pluto’s rotational axis. Taken at face value, this ellipticity could imply wind speeds of up to twice the sonic speed (~200 m/s), which would be difficult to explain. Similar distortions have been reported for Triton's atmosphere (Elliot, J. L., et al., Icarus 148, 347). This work has been supported in part by Research Corporation, the Air Force Research Laboratory, NSF, and NASA.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.