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Published February 8, 2005 | Supplemental Material + Published
Journal Article Open

Atmosphere of Callisto


During the Galileo flybys of Callisto in 1999, a CO_2 atmosphere and an ionosphere were detected. Using the Caltech/Jet Propulsion Laboratory one-dimensional KINETICS model, we have successfully simulated the observed electron density within a factor of 2, while satisfying the observational constraints on carbon and oxygen atoms. We conclude that photoionization of CO_2 alone is insufficient to produce the observed electron density. An atmosphere 20–100 times denser than the CO_2 atmosphere must be introduced, as suggested by Kliore et al. (2002). We show that an O_2-rich atmosphere is highly probable. However, the atomic oxygen produced from O_2 photodissociation is 2 orders of magnitude greater than the upper limit given by Strobel et al. (2002). The introduction of reactive hydrogen chemistry assuming a surface abundance of H_2O of ∼2 × 10^9 cm^(−3) (4 × 10^(−8) mbar) is required to reduce the excess atomic O abundance. The calculated atomic O column density is >5 × 10^(12) cm^(−2), which is about the observed upper limit, suggesting we should be able to detect O in the atmosphere of Callisto.

Additional Information

© 2005 The American Geophysical Union. Received 11 July 2004; Revised 17 October 2004; Accepted 1 December 2004; Published 8 February 2005. We thank M. Gerstell, R. L. Shia, D. J. Stevenson, and D. F. Strobel for valuable discussions. This research was supported in part by NASA grant NAG5-6263 to the California Institute of Technology. B.F.L. gratefully acknowledges the support of a Pappalardo Fellowship in Physics of MIT.

Attached Files

Published - jgre1905.pdf

Supplemental Material - jgre1905-sup-0001-tab01.txt

Supplemental Material - jgre1905-sup-0002-tab02.txt


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