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Updated: Jul 11, 2026

Bringing the Visible Universe into Focus with Robo-AO
Published on: February 12, 2013
An Atmosphere on Ganymede from Its Occultation of SAO 186800 on 7 June 1972
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, - approximately 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, + approximately 0.2) grams per cubic centimeter.
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