Abstract
Stellar occultations—the passing of a relatively nearby body in front of a background star—can be used to probe the atmosphere of the closer body with a spatial resolution of a few kilometres (ref. 1). Such observations can yield the scale height, temperature profile, and other information about the structure of the occulting atmosphere. Occultation data acquired for Pluto's atmosphere in 1988 revealed a nearly isothermal atmosphere2 above a radius of ∼1,215 km. Below this level, the data could be interpreted as indicating either an extinction layer or the onset of a large thermal gradient, calling into question the fundamental structure of this atmosphere. Another question is to what extent Pluto's atmosphere might be collapsing as it recedes from the Sun (passing perihelion in 1989 in its 248-year orbital period), owing to the extreme sensitivity of the equilibrium surface pressure to the surface temperature. Here we report observations at a variety of visible and infrared wavelengths of an occultation of a star by Pluto in August 2002. These data reveal evidence for extinction in Pluto's atmosphere and show that it has indeed changed, having expanded rather than collapsed, since 1988.
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Acknowledgements
Setting up the equipment and recording the occultation data proved to be a challenge, and we appreciate the assistance of G. Koenig, L. Berkgnut, T. Denault, P. Sears, R. Stone, D. Severinsen, A. Pickles and T. Carroll. We thank the staff of the Maui Space Surveillance System for their assistance in taking the Haleakala data, and we thank B. Sicardy et al. for communication of results before publication. The United Kingdom Infrared Telescope is operated by the Joint Astronomy Centre on behalf of the UK Particle Physics and Astronomy Research Council. This work was supported, in part, by Research Corporation, the Southwest Research Institute, NSF and NASA. L.C.R. and D.T.H. were supported by Air Force Research Laboratory/Directed Energy.
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Elliot, J., Ates, A., Babcock, B. et al. The recent expansion of Pluto's atmosphere. Nature 424, 165–168 (2003). https://doi.org/10.1038/nature01762
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DOI: https://doi.org/10.1038/nature01762
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