HST/FOS Observations of Io in the Near Ultraviolet
K.L. Jessup, G.E. Ballester, J.T. Clarke (University of Michigan), D.F. Strobel (John Hopkins University), N. Schneider (University Colorado), M. McGrath (Space Telescope Institute), M. Combi (University of Michigan), J. Ajello (JPL), J.L. Luhmann (IGPP, UCLA), X. Zhu (John Hopkins University)
We present initial results arising from the comparison of four
sets of Hubble Space Telescope/Faint Object Spectrograph near
ultraviolet observations obtained in the four year period from
August 1993 until October 1996. As an initial diagnositc, we have
obtained the ratios of: small apeture (0.3") pre-COSTAR FOS/BL
spectra of Pele and a known bright region, obtained on August 1993;
disk integrated spectra of Io immediately after eclipse egress and 1
hour post egress obtained on October 1996 with FOS/RD; and disk
integrated spectra of Io at eastern and western elongation obtained on
1994 with FOS/BL and again in October 1996 with FOS/RD. With these
ratios, we have indentified the relative differences in the SO2
absorption signature within each individual data set, and temporally
between each data set. Future work on these spectra will include
careful evalutation and modeling of the geometric albedoes associated
with each spectra. Comprehensive analysis and comparision of these
results should provide constraints useful in separating the sublimation
and volcanic components of Io's SO2 atmosphere, identifying the
dominant source of SO2 gas and determining limits of the abundance
and spatial distribution of the SO2 atmospheric component.
This research has been supported by the STScI grants GO-5438 and
GO-6786, and by the Univeristy of Michigan.