31st Annual Meeting of the DPS, October 1999
Session 58. Io Posters
Poster Group II, Thursday-Friday, October 14, 1999, , Kursaal Center

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[58.07] The Relationship Between Ios Sodium Clouds and Volcanic Activity on Io

M. Mendillo, J. K. Wilson, J. Baumgardner (Boston University), N. M. Schneider (LASP/University of Colorado), J. Spencer, J. Stansberry (Lowell Observatory), B. Flynn (CEA/UC Berkeley), J. T. Trauger (JPL)

Io's extended sodium clouds are populated by atmospheric sodium atoms whose ultimate source is volcanic activity on Io. Multiple-scale images of sodium emission around Jupiter and accompanying numerical models indicate that the clouds are generated primarily by two atmospheric escape processes on Io: atmospheric sputtering, and dissociation or dissociative recombination of an unknown sodium-bearing molecular pickup ion (NaX+). Atmospheric sputtering produces the "banana" cloud near Io and a diamond-shaped sodium "nebula" which extends out to a few hundred Jovian radii from Jupiter. Dissociation of NaX+ produces the peculiar "stream" feature and a rectangular-shaped nebula.

Volcanic activity on Io, as characterized by infrared emission from Ios sub-Jovian hemisphere, appears to affect the relative importance of the two escape processes. Infrared observations, including new data from 1994-1996, show a trend of low volcanic activity when atmospheric sputtering is the major escape process, and above-normal volcanic activity when NaX+ dissociation is occurring at significant rates. Thus, volcanic activity on Ios sub-Jovian hemisphere appears to enhance the escape of NaX+ from Ios atmosphere. This may indicate that either NaX+ or a molecule necessary for its formation is introduced by the eruptions. It is also possible that the eruptions change the structure and/or dynamics of Ios atmosphere so as to affect the chemical formation, escape, or destruction of atmospheric NaX+.


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The author(s) of this abstract have provided an email address for comments about the abstract: jkwilson@bu.edu

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