Observations with the Visual and Infrared Mapping Spectrometer (VIMS) during Cassini's flyby of Jupiter
Sotin, C.; Brown, R. H.; Baines, K. H.; Buratti, B. J.; Clark, R. N.; Nicholson, P. D.; Bibring, J. -P.; Langevin, Y.; Bellucci, G.; Jaumann, R.; Drossart, P.; Mennella, V.; Capaccioni, F.; McCord, T. B.; Hansen, G.; Cruikshank, D. P.; Sicardy, B.; Cerroni, P.; Coradini, A.; Formisano, V.; Matson, D. L.; Nelson, R. M.; Filacchione, G.; Showalter, M.; Hibbitts, K.; Amici, S.; Chamberlain, M. A.
United States, Italy, France, Germany
Abstract
The Cassini Visual and Infrared Mapping Spectrometer (VIMS) is an imaging spectrometer covering the wavelength range 0.3-5.2 μm in 352 spectral channels, with a nominal instantaneous field of view of 0.5 mrad. The Cassini flyby of Jupiter represented a unique opportunity to accomplish two important goals: scientific observations of the jovian system and functional tests of the VIMS instrument under conditions similar to those expected to obtain during Cassini's 4-year tour of the saturnian system. Results acquired over a complete range of visual to near-infrared wavelengths from 0.3 to 5.2 μm are presented. First detections include methane fluorescence on Jupiter, a surprisingly high opposition surge on Europa, the first visual-near-IR spectra of Himalia and Jupiter's optically-thin ring system, and the first near-infrared observations of the rings over an extensive range of phase angles (0-120°). Similarities in the center-to-limb profiles of H +3 and CH 4 emissions indicate that the H +3 ionospheric density is solar-controlled outside of the auroral regions. The existence of jovian NH 3 absorption at 0.93 μm is confirmed. Himalia has a slightly reddish spectrum, an apparent absorption near 3 μm, and a geometric albedo of 0.06±0.01 at 2.2 μm (assuming an 85-km radius). If the 3-μm feature in Himalia's spectrum is eventually confirmed, it would be suggestive of the presence of water in some form, either free, bound, or incorporated in layer-lattice silicates. Finally, a mean ring-particle radius of 10 μm is found to be consistent with Mie-scattering models fit to VIMS near-infrared observations acquired over 0-120° phase angle.