AAS 201st Meeting, January, 2003
Session 61. Pluto-Occultation Studies
Oral, Tuesday, January 7, 2003, 10:00-11:30am, 616-617

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[61.03] Examination of Pluto's Atmospheric Figure with the P131.1 Stellar Occultation

M. J. Person, J. L. Elliot, K. B. Clancy (MIT), D. J. Tholen, J. T. Rayner (U. of Hawaii), J. M. Pasachoff, B. A. Babcock, D. R. Ticehurst (Williams), D. Hall, L. C. Roberts, Jr. (Boeing), A. S. Bosh (Boston U. and Lowell), S. S. Eikenberry, D. S. Moon (Cornell I.), M. W. Buie, E. W. Dunham, C. B. Olkin, B. Taylor (Lowell), S. D. Kern, D. J. Osip, S. Qu, C. V. Salyk (MIT), S. K. Leggett (UKIRT), S. E. Levine, R. C. Stone (USNO)

From the 1988 stellar occultation by Pluto, Millis (et al., Icarus, 105, 282) did not report any deviation from sphericity in Pluto's atmospheric figure. However, stellar occultation measurements of Triton throughout the late 1990's revealed a significant deviation from a spherical figure in Triton's atmospheric shape (Elliot et al., Icarus, 148, 347, and Person 2001, S.M. Thesis, Dept. of Earth Atmos. and Plan. Sci., Mass. Inst. Of Tech., Cambridge MA). This deviation is unexpected since Triton's rotation period is slow (5.88 days), but the resulting non-spherical shape could be due to high winds. The Triton results have prompted us to examine Pluto's atmospheric figure with more recent data.

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 since the Triton results to measure such non-sphericity in Pluto's atmosphere. The occultation was observed from numerous stations in Hawaii and the western United States (see Elliot et al., Pasachoff et al., Clancy et al., this conference). We present the results of our analysis of these datasets in searching for non-spherical deviations in 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 datasets from the various Mauna Kea telescopes are redundant with each other in figure space, but provide valuable cross checks among their timing systems. 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. As a second measure of possible non-sphericity, the individual light curves can be individually fit with atmospheric models in the manner of Elliot and Young (AJ, 103, 991), to search for asymmetry indicative of a non-circular atmospheric cross section around the limb of the planet. This work has been supported in part by Research Corporation, NASA, and NSF.

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