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[18.14] Mesospheric CH₄ and ionospheric H₃⁺ emission in the CASSINI/VIMS observations of Jupiter at mid-latitudes

P. Drossart (Obs. Paris), K.H. Baines (JPL), G. Bellucci (IFSI, Rome), J.P. Bibring (IAS, Orsay), R.H. Brown (U. Arizona), B.J. Buratti (JPL), F. Capaccioni, P. Cerroni (IASF, Rome), R.N. Clark (USGS, Denver), A. Coradini (IASF, Rome), D.P. Cruikshank (NASA/Ames), V. Formisano (IFSI, Rome), R. Jaumann (DLR, Berlin), Y. Langevin (IAS, Orsay), D. Matson (JPL), T.B. McCord (U. Washington), V. Mennella (U. Naples), R.M. Nelson (JPL), P.D. Nicholson (Cornell U.), B. Sicardy (Obs. Paris), C. Sotin (U. Nantes), VIMS Team

Cassini/VIMS observations during the Jupiter encounter between December 2000 and January 2001 give the first opportunity to study phase angle variations of H₃⁺ emission at 3.5~\mum, together with fluorescence CH₄ emission at a high level of sensitivity. Spectral images with long integration time (640 ms) are used, for maximum sensitivity. The spectrum of Jupiter in the 3.3-3.6~\mum range exhibits H₃⁺ thermal emission and CH₄ emission, interpreted as due to fluorescence of solar light (Drossart et al., ESA-SP427 1999). Synthetic spectra confirms this later detection, first seen on ISO/SWS at a global scale on the disk, and reproduces the P/Q/R branches of the \nu₃ band of CH₄.\\ Limb profiles of the CH₄ emission are obtained for various phase angles, between 0 and 70 dg, which give a new constraint on the mesospheric sounding.\\ On the other hand, limb profiles of H₃⁺ thermal emission are consistent with a H₃⁺ density controlled by the solar flux, confirming the solar control on the H₃⁺ density in equatorial and mid latitude regions, in contrast with high latitude auroral emissions.

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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.