HR: 0830h
AN: P51B-0448    [PDF]
TI: Composition and Variability of Io's Pele Plume
AU: * Jessup, K
EM: k.l.jessup@lowell.edu
AF: Lowell Observatory, 1400 W Mars Hill RD, Flagstaff, AZ 86001 United States
AU: Spencer, J
EM: spencer@lowell.edu
AF: Lowell Observatory, 1400 W Mars Hill RD, Flagstaff, AZ 86001 United States
AU: Ballester, G
EM: gilda@vega.lpl.arizona.edu
AF: Lunar and Planetary Lab, University of Arizona, Tucson, AZ 85721 United States
AU: Yelle, R
EM: yelle@lpl.arizona.edu
AF: Lunar and Planetary Lab, University of Arizona, Tucson, AZ 85721 United States
AB: The Pele plume is one of the largest and most dynamic of the plumes on Io. Various observations have been made to characterize the composition and eruptive behavior of this plume. Within the last $\sim$ 15 years the column density of sulfur dioxide (SO$_2$) gas within the plume has been derived using both spectral and imaging observations. Elemental sulfur (S$_2$), which has long been suspected to be a major constituent of the Pele plume based on the color of its deposits, has only recently been positively identified within the plume. And, the current SO/SO$_2$ ratio accepted for the Pele plume is based on high signal-to-noise (S/N) spatially resolved spectra taken three years prior to the S$_2$ detection. These results have been useful as a probe of magma chemistry and vent conditions. However, because the Pele plume has long been known to be variable in its eruptive behavior, observational constraint of each of the possible plume constituents based on a single observation would greatly decrease the uncertainty in the modeling of Pele's eruption chemistry and magma state. For this reason, in February and March 2003 we obtained spectra of Pele with Hubble's Space Telescope Imaging Spectrograph (STIS) in transit of Jupiter, using the 0.1 arcsec slit, for the wavelength region extending from 2100-3100 A. Because these data were obtained in four visits of 1020s each, an integration time that is four times longer than that used in the initial S$_2$ detection, the higher S/N may be sufficient to allow reliable estimates of the SO$_2$, S$_2$, and SO gas abundances to be made independent of uncertainties with respect to temporal variability of the plume for the first time. We present preliminary analysis of these data reporting the SO$_2$, S$_2$, and SO abundances of the Pele plume. We also obtained UV and visible-wavelength images of the plume in reflected sunlight with the Advanced Camera for Surveys (ACS) prior to Jupiter transit, in order to constrain plume dust abundance. We will give a brief overview of the variability of the plume as a function of time during the $\sim$ 1 month period spanned by the observations, in both reflected and transmitted light.
DE: 5405 Atmospheres--composition and chemistry
DE: 5464 Remote sensing
DE: 5480 Volcanism (8450)
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting