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K. L. Jessup, J. R. Spencer (Southwest Research Institute), R. Yelle (University of Arizona)
In February 2003, March 2003 and January 2004 Pele plume transmission spectra were obtained during Jupiter transit with Hubble's Space Telescope Imaging Spectrograph (STIS), using the 0.1 arcsec long slit and the G230LB grating. The STIS spectra covered the 2100-3100 wavelength region and extended spatially along Io's limb both northward and westward of Pele.These observations were a repeat of the 1999 STIS observations from which S2 gas within the Pele plume was first positively identified and direct measure of the SO2 /S2 ratio in the plume was first reported (Spencer et al. 2000). The S2 and SO2 absorption signatures evident in the newly acquired STIS data indicate that the gas signature at Pele was temporally variable. Additionally, the S2 gas absorption signature was observed at other latitude and longitudes, suggesting the presence of other S2 bearing plumes on Io. Contemporaneous with the spectral data UV and visible-wavelength images of the plume were obtained in reflected sunlight with the Advanced Camera for Surveys (ACS) prior to Jupiter transit. The dust scattering recorded in these data provide an additional qualitative measure of plume activity on Io indicating that the degree of dust scattering over Pele varied as a function of the date of observation, and that there were several other dust bearing plumes active just prior to Jupiter transit. We will present constraints on the composition and variability of the gas abundances of the Pele plume as well as other S2 bearing plumes recorded within the STIS data, as a function of time.
This work has been funded by Planetary Astronomy grant, NAG5-13350.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.