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The structure of Io's thermal corona and implications for atmospheric escape

Summers, M. E. and Strobel, D. F. and Yung, Y. L. and Trauger, J. T. and Mills, F. (1989) The structure of Io's thermal corona and implications for atmospheric escape. Astrophysical Journal, 343 (1). pp. 468-480. ISSN 0004-637X. doi:10.1086/167720.

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We investigate the escape of species from Io's atmosphere using a steady-state model of Io's exospheric corona and its interaction with the Io plasma torus. The corona is assumed to be spherically symmetric with the radial density and compositional structure determined by the gas kinetic temperature, critical level radius, and mixing ratios of the component species. Thermal and nonthermal escape rates are calculated and the results compared with previously estimated torus and neutral cloud supply rates for O, S, Na, and K. Both oxygen- and sulfur-dominated exospheres are considered. Atmospheric sputtering is found to be the major escape mechanism for models in which the plasma flow reaches the critical level. However, such models produce total mass-loading rates an order of magnitude larger than inferred values suggesting that either (1) the structure of the thermal corona is significantly modified by the nonthermal interaction, or (2) substantial plasma flow modification and deflection occurs in the corona at or above the critical level. Assuming that the thermal model is a correct description of the corona, a comparison of these results with the observed near-Io distribution of neutral Na and estimated source rates for the neutral Na "jets" suggests an extended Na coronal component. Assuming that this component is part of the thermal exosphere, we find that the observations are consistent with an O-dominated corona, an exospheric temperature ~1000 K, a 0.001 critical level mixing ratio of Na, and a critical level radius ~1.5 R_(Io).

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Yung, Y. L.0000-0002-4263-2562
Additional Information:© 1989 American Astronomical Society. Provided by the NASA Astrophysics Data System. Received 1986 August 14; accepted 1989 January 5. The authors thank W. H. Smyth, N. Schneider, E. Sittler, and G. Ballester for useful discussions on this topic. This work was supported by the National Aeronautics and Space Administration, contract NAGW-648 and the Voyager Mission.
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Subject Keywords:planets: magnetospheres - planets: satellites
Issue or Number:1
Record Number:CaltechAUTHORS:20140912-084209603
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:49637
Deposited By: Tony Diaz
Deposited On:12 Sep 2014 23:58
Last Modified:10 Nov 2021 18:46

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