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J.C. Granahan, J. Sweet (BAE SYSTEMS), F.P. Fanale (University of Hawaii), R.W. Carlson, W.D. Smythe (Jet Propulsion Laboratory), Galileo NIMS Team, Galileo SSI Team
A variety of indicators for silicate volcanism on Io have been observed by the Galileo spacecraft. These include high temperature volcanism ( McEwen et al., 2000 and  Lopes-Gautier et al., 2000) of up to 1700 K, a 0.9 micrometer absorption present in many dark (and relatively recent) lava flows ( Geissler et al., 1999), and large scale releif in f the form of mountains ( Turtle et al., 2000). The 0.9 micrometer feature can be interpreted as absorption feature due to pyroxene. This detection was accomplished via the Galileo SSI (Solid State Imager) camera system which utilizes a set of up to 8 discrete filters to sample the wavelength range from 0.4-1.0 micrometers. Orthopyroxene has an absorption feature around 2.0 micrometers. Our study seeks to analyze the infrared signatures that correlate to this 0.9 micrometer feature. The Galileo Near Infrared Mapping Spectrometer (NIMS) collects data from 0.7-5.2 micrometers with up to 408 bands during the nominal mission and with 12 bands during the current mission. Initial results indicate that these dark features appear to have lower concentrations of sulfur dioxide than surrounding surfaces and do not directly correlate to the 1.2 micrometer absorption feature found by NIMS on Io. Although not detected in our initial NIMS spectral survey, we are modeling spectral mixtures to determine the maximum amount of orthopyroxene that can be present in the NIMS observations.
[1 & 2] EOS, Trans, Vol. 81, No. 19, Supplement, S288,  Icarus, 140, 265,  EOS, Trans, Vol. 81, No. 19, Supplement, S289.
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