Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001dps....33.2406s&link_type=abstract
American Astronomical Society, DPS Meeting #33, #24.06; Bulletin of the American Astronomical Society, Vol. 33, p.1083
Astronomy and Astrophysics
Astronomy
Scientific paper
The nature of Io's atmosphere with its strong interaction with the Io plasma torus is a complex three-dimensional problem of significant scientific interest. To gain more physical insight into this problem, new numerical calculations for Io's atmosphere have been undertaken based upon an improved version of the 2-D (altitude and solar zenith angle) multi-species diffusive hydrodynamic model of Wong and Smyth (Icarus 146, 60-74, 2000) for an SO2 sublimation atmosphere with photo- and gas-phase chemistry for the species SO2, SO, O2, O, S, Na, NaO, and NaS. First, plasma-neutral chemistry (in particular, electron impact molecular dissociation) has been incorporated in the 2-D model in a simplified manner. Model calculations show that electron impact molecular dissociation is important at higher altitudes in the dayside atmosphere, over a larger altitude range in the thinner nightside atmosphere, and in Io's entire atmosphere when eclipsed by Jupiter's shadow. In particular, O, S and SO are enhanced dramatically relative to the SO2 density at high altitudes in the dayside atmosphere and are the dominant species in the nightside atmosphere. Plasma-neutral chemistry also significantly stabilizes the abundance of O and S in Io's eclipsed atmosphere, so as to be more compatible with eclipse and post-eclipse changes observed in O and S ultraviolet intensities obtained with HST (Ballester et al., BAAS 29, 980, 1997). Second, relevant photo- and gas-phase chemistry for chlorine species (which can be strongly coupled through Cl2 to sodium species) has been incorporated in the 2-D hydrodynamic model, and exploratory calculations have being undertaken for different source scenarios. Atomic chlorine was recently detected in UV emission lines acquired by HST/STIS measurements (Retherford et al., BAAS 32, 1055, 2000). Model calculations will be presented to illustrate the impact of plasma-neutral chemistry and the distribution of chlorine and sodium species in Io's atmosphere.
Marconi Max L.
Smyth William H.
Wong Chuen-Ming M.
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