An Atmosphere on Ganymede from Its Occultation of SAO 186800 on 7 June 1972

Creators: Carlson, R. W.; Bhattacharyya, J. C.; Smith, B. A.; Johnson, T. V.; Hidayat, B.; Smith, S. A.; Taylor, G. E.; O'Leary, B.; Brinkmann, R. T.

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Abstract

On 7 June 1972 the third, Jovian satellite Ganymede occulted the eighth-magnitude star SAO 186800. Successful photoelectric observations obtained at Lembang, Java (Indonesia), and Kavalur, India, show nonabrupt immersions and emersions, indicating the presence of an atmosphere whose surface pressure is greater than about 10^(-3) millibar. By fitting the two occultation durations as chords to a model disk, the diameter is found to be 5270 (+30, -∼200) kilometers, the major error contribution arising from the uncertain atmospheric thickness below the occultation layer. The derived mean density is 2.0 (-0.03, + ∼0.2) grams per cubic centimeter.

Additional Information

© 1973 American Association for the Advancement of Science. Received 30 April 1973; revised 12 July 1973. We acknowledge with thanks the special efforts of W. Brunk and others at the National Aeronautics and Space Administration in granting funds for the American expeditions on short notice (under NASA grant NGR 05-036-005 with B.O. as principal investigator and coordinator of results). T.V.J. is a National Research Council resident research associate. We also thank B. J. Harris of Perth Observatory, Australia, and J. Churms and T. W. Russo of Capetown Observatory, South Africa, for providing the photographic plates used in refining the predictions; D. T. Vu for supplying photoelectric data; U.S. Information Service personnel at the U.S. Embassy in Jakarta and G. Edwards of the Australian News and Information Bureau for their assistance in the American expeditions; and C. Durrington, Qantas Airlines, and British Overseas Airline Company for their special help in getting the necessary equipment to Darwin, Australia.

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