36th DPS Meeting, 8-12 November 2004
Session 9 Galilean Satellites
Oral, Tuesday, November 9, 2004, 8:30-10:00am, Clark

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[9.02] Variability and Composition of Io's Pele Plume

K.L. Jessup, J. Spencer (SWRI), R. Yelle (U. of Arizona)

The Pele plume is one of the largest and most dynamic of the plumes on Io. While sulfur dioxide (SO2) gas was always assumed to be a constituent of this plume, spectral observations obtained in 1999 were the first to positively identify elemental sulfur (S2) (Spencer et al. 2000) within the Pele plume. The S2/SO2 ratio derived from this observation provided a critical component necessary for the constraint of the magma chemistry and vent conditions of the Pele plume (Zolotov and Fegley 1998). But, because the Pele plume has long been known to be variable in its eruptive behavior, it is not likely that the vent conditions are invariant. Consequently, additional observations were needed to constrain the extent of the variability of the plume’s composition and gas abundances. To this end, in February 2003, March 2003 and January 2004 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 Å. Contemporaneous with the spectral data 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. The newly acquired STIS data show both the S2 and SO2 absorption signatures, and provide concrete evidence of temporal variability in the abundance of these gases. Likewise, the degree of dust scattering recorded in the ACS data varied as a function of the date of observation. We will present preliminary constraints on the composition and variability of the gas abundances of the Pele plume as recorded within the STIS data. We will also give a brief overview of the variability of the plume dust signatures relative to the gas signatures as a function of time.

The author(s) of this abstract have provided an email address for comments about the abstract: k.l.jessup@boulder.swri.edu

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Bulletin of the American Astronomical Society, 36 #4
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