Sulfur volcanism on Io

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" wide slit and the G230LB grating. The STIS spectra covered the 2100-3100 A wavelength C regions and extended spatially along Io's limb encompassing the region directly above and northward of the vent of the Pele volcano. The S-2 and SO2 absorption signatures evident in these data indicate that the gas signature at Pele was temporally variable, and that an S2 absorption signature was present similar to 12 degrees from the Pele vent near 6 5 S and 264 15 W, suggesting the presence of another S2 bearing plume on To. 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 To, 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 during the observations. We present constraints on the composition and variability of the gas abundances of the Pele plume as well as the plumes detected by ACS and recorded within the STIS data, as a function of time. (c) 2007 Elsevier Inc. All rights reserved.