[Previous] | [Session 74] | [Next]
M.C. Wong, W.H. Smyth (AER, Inc.)
In addition to gas supply from volcanic plumes, surface sublimation is believed to be an important source for Io's atmosphere. The abundances of condensible species (e.g. SO2, S, and O) in a sublimation atmosphere are sensitive functions of the surface frost temperature which adjusts to solar radiation in short time scales (~ tens of minutes). Therefore, as Io enters and exits Jupiter's shadow (an interval of ~ 2.3 hours) along its orbit, a collapse and re-establishment of a sublimation atmosphere can be expected. Recent eclipse observations have measured 1) a decrease and increase of S and O abundances during ingress and egress, respectively (Ballester et al. 1997, BAAS 29, 980); 2) an increase of Na abundance by a factor of ~ 4 in the hour following an egress (Harris et al. 1999, abstract in MOP meeting, Paris); 3) a decrease of ~ 30 brightness (despite an increase of local emission from volcanoes) in comparing images acquired 11 and 53 minutes after Io had entered into eclipse (Geissler et al. 1999, paper submitted to Science), further reconfirming the role of a sublimation atmosphere. Model calculations have been performed to explore the time dependent behavior of Io's sublimation atmosphere. It is found that different species in the atmosphere possess different time scales in response to the changes in surface temperatures and photochemistry resulting from Io being shadowed from and re-exposed to sunlight. Furthermore, it is found that different atmospheric regions (dayside and nightside atmospheres before entering and exiting the shadow) exhibit different transient behaviors. The results of the calculations will be presented at the meeting.
The author(s) of this abstract have provided an email address for comments about the abstract: mau@aer.com