Io's Changing Atmosphere: Constraints on the ambient temperature and SO/SO2 ratio as a function of orbital phase

Details Io's Changing Atmosphere: Constraints on the ambient temperature and SO/SO2 ratio as a function of orbital phase Io's Changing Atmosphere: Constraints on the ambient temperature and SO/SO2 ratio as a function of orbital phase

Dec 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000dps....32.6519j&link_type=abstract

American Astronomical Society, DPS Meeting #32, #65.19; Bulletin of the American Astronomical Society, Vol. 32, p.1642

Astronomy and Astrophysics

Astronomy

Scientific paper

We characterize the behavior of Io's atmosphere as a function of orbital phase, based on Hubble Space Telescope/Faint Object Spectrograph (HST/FOS) near ultraviolet disk-integrated spectra of Io at east (90 CML) and west (270 CML) elongation obtained in both 1994 and 1996, as well as disk-integrated spectra of Io taken within the first 2 hours post-eclipse egress obtained in 1996. We present fitted SO2 gas temperatures and the SO/SO2 ratios determined from SO and SO2 column abundances constrained from an exploratory study of the spectral signature effects of volcanic SO and SO2 output, atmospheric and volcanic temperature, and the degree to which the SO and SO2 gas components are spatially confined or extended. The results of the study indicate that at initial egress the temperature of the extended (ambient) SO2 gas component was 350+/- 25K, however, ~ 1.8 hrs later the gas temperature dropped by ~ 150 K to 175 +/- 25K; whereas for the east and west elongation albedoes the fit temperatures, are respectively 125+/- 25K and 175+/- 25K for the 1994 observations, and 250+/- 25K and 200+/- 25K for the 1996 observations. In each case the fitted gas temperature of the extended (i.e. the non-volcanically confined component) SO2 component is independent of the assumed spatial distribution. Likewise, the SO/SO2 ratios constrained from the total SO and SO2 columns show little dependence on the assumed spatial distribution of the extended gases. Instead, the SO/SO2 ratio of the fully sunlit elongation albedoes ranges from 2-13% and increases with increasing temperature. Interestingly, the SO/SO2 ratio of the egress albedoes ranges from 1-25% depending on the time after egress, and appears to be anti-correlated with the fitted SO2 gas temperatures. The implication is that the atmospheric process(es) determining the SO abundance at initial egress was/were different from that/those in control when Io was in full sunlight. This research has been funded by NASA Grant NGT5-50154.

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