Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm11c1778d&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM11C-1778
Physics
[2732] Magnetospheric Physics / Magnetosphere Interactions With Satellites And Rings, [5405] Planetary Sciences: Solid Surface Planets / Atmospheres
Scientific paper
The extended neutral cloud of atomic sodium that follows Io on its orbit was detected by Brown (1974), thanks to its large cross section for resonant scattering of visible sunlight. S and O neutral clouds were also detected, albeit with limited observational constraints on their size and density (Brown,1981; Durrance et al., 1995; Wolven et al., 2001). These extended neutral clouds are thought to be fed by ion sputtering of the atmosphere, a process by which an ion impinging Io’s atmosphere triggers a cascade of collisions and eventually ejects an atom (or molecule) at low speed (McGrath and Johnson, 1987). We investigate here an alternative process that could supply the S and O extended neutral clouds: the electron impact dissociation of the SO2 atmosphere of Io. Multi-species chemical modeling of the interaction of Io’s atmosphere and the plasma torus (Dols et al., 2008) suggests that the rate of dissociation of SO2 by electron impact is high (several tons/sec) because of the low threshold energy (5.7 eV) for impact dissociation. Laboratory experiments of electron impact dissociation of SO2 show that the velocity of the S and O atoms resulting from the dissociation of SO2 by electron impact has an average velocity of a few km/s (Vatti Pale et al. 2004). When electron impact dissociation occurs at Io, such velocities imply that some atoms resulting from dissociation might escape the gravitational field of Io and might be able to feed an extended neutral cloud along the orbit of Io. We use the dissociation rate and volume computed from the chemical modeling of Dols et al. (2008), the velocity distribution of S and O from laboratory experiments of Vatti Palle et al. (2004) as input to the Monte Carlo modeling of neutral cloud formation of Burger et al. (2007) to investigate the resulting shape and neutral density of the extended S and O clouds and compare with the available observations. Brown R.A. ”The Jupiter hot plasma torus: Observed electron temperature and energy flows”. Astrophys. J., 244, 1072-1080, 1981. Burger M.H. et al. “Understanding the escape of water from Enceladus”. J. Geophys. Res, 112, A06219, 2007. Dols V. et al., “A multi-species chemistry model of Io’s local interaction with the plasma torus”. J. Geophys. Res., 113, 2008. Durrance S.T. et al., “Neutral sulfur emission from the Io torus measured with the Hopkins Ultraviolet Telescope”. Astrophys. J., 447, 408-415, 1995. McGrath M.A. and R.E. Johnson. ”Magnetospheric plasma sputtering of Io’s atmosphere”. Icarus, 69, 519-531, 1987. Vatti Palle P. et al. “High resolution far ultraviolet spectrum of electron-excited SO2”. J. Geophys. Res., 109, 2004. Wolven et al., “Emission profiles of neutral oxygen and sulfur in Io’s exospheric corona”. J. Geophys. Res., 106, 26,155-26, 182, 2001.
Bagenal Fran
Burger Matthew Howard
Delamere Peter A.
Dols V. J.
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