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L.W. Esposito, A.I.F. Stewart, A.R. Hendrix, W.R. Pryor (LASP, University of Colorado), UVIS Team
The Cassini Ultraviolet Imaging Spectrograph (UVIS) is part of the remote sensing payload of the NASA/ESA Cassini spacecraft, now en route to Saturn. This spectrograph includes channels for extreme UV and far UV spectroscopic imaging, high speed photometry of stellar occultations, solar EUV occultation, and a hydrogen/deuterium absorption cell. Our current science results are from cruise observations. On 17 January 1999, UVIS observed the bright star, Spica. The UVIS spectra are in good agreement with Copernicus and with stellar atmosphere models. On 24 June 1999, the Cassini spacecraft passed within 600 km of the surface of Venus. Prominent features in the FUV spectra include HI 121.6 nm, OI 130.4 and 135.6 nm, CI 156.1 and 165.7 nm, and the CO Fourth Positive bands. Weaker features of NI, CI, CII, OI and CO are also present. The EUV spectrum contains well-defined features at HeI 58.4 nm, OII 83.3 nm, OI 98.9 nm, and HI 102.6 nm. Weaker emissions include OI 104.1 nm, CO (C-X) 108.8 nm, NI 113.5 nm, and a blend of CO (B-X) and OI near 115 nm. On 18 August 1999, UVIS observed the Earth's moon for 34 minutes. The FUV spectra show a smooth, flat refectance consistent with pure solar reflection. Comparison of highlands and maria spectra show the maria to be bluer, consistent with Apollo 17 and lab results. No lunar emission features are seen. UVIS has begun a systematic program of iterplanetary hydrogen and helium observations, including HeI 58.4 nm, and HI 102.6 (Lyman-beta) and 121.6 nm (Lyman-alpha). These data can strongly constrain the distribution of interstellar hydrogen and helium flowing through the solar system. Observations of the Jupiter system begin 1 October 2000 and continue through 22 March 2001. We present some typical results and discuss plans for Saturn.