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M. H. Burger, N. M. Schneider (University of Colorado/LASP), J. K. Wilson (Boston Univeristy/Center for Space Physics)
Io's atmosphere is continuously lost due to interactions with Jupiter's magnetic field and the Io plasma torus. Neutral sodium is observed escaping through three distinct mechanisms: sputtering, charge-exchange, and molecular dissociation. Sputtering of sodium off Io's atmosphere results in an extended neutral cloud leading Io in its orbit. Ion-neutral charge exchange in Io's ionosphere results in a jet of fast sodium seen ejected from Io's anti-Jovian hemisphere. An additional stream of fast sodium is seen originating in the plasma torus and points to a source of molecular sodium ions escaping from Io. The relative intensities of these three features points to differences in the methods of atmospheric escape important at Io.
Images taken from the Catalina Observatory 61'' telescope using the LPL Coronograph during Jupiter's last two apparitions have shown great variability in the brightness of Io's sodium features. We use a numerical simulation of sodium atoms ejected from Io's exobase to determine the causes of variability in the extended neutral cloud. Variations in the escape rates of neutral sodium from Io's exobase and the effects of the plasma torus on loss of sodium in the neutral cloud are examined. We also look at changes in the relative intensities of the three primary sodium features. Model images and animations of the fast sodium jet and the molecular ion stream can be found at the web address given.
This work is supported at the University of Colorado by NASA's Planetary Astronomy Program and at Boston University by NASA's Magnetospheric Physics and Planetary Astronomy Programs.
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