DPS 2001 meeting, November 2001
Session 3. Cassini and Galileo at Jupiter I
Oral, Chairs: F. Bagenal, C. Porco, Tuesday, November 27, 2001, 11:10am-12:30pm, Regency E

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[3.08] The upper atmosphere of Jupiter from VLT/ISAAC observations

P. Drossart, T. Fouchet, E. Raynaud, B. Sicardy, T. Widemann (DESPA, Paris Obs.), J. H. Waite (Univ. Michigan), G. R. Gladstone (SwRI)

Observations of Jupiter were performed during the Cassini/Jupiter encounter, between December 13 and 14, 2000, with the ISAAC imaging spectrometer of the ESO/VLT ANTU telescope. Long slit spectra of Jupiter were recorded on the central meridian, between 3.30 and 3.56 \mum, at a spectral resolution of \approx1200, and a spatial resolution of 1 arcsec, covering the longitude (System III) range between 200-350dg and 340-140dg, respectively, during the two nights. Several scientific objectives are achievable through these observations. In the North and South auroral regions, H3+ emission is observed at a S/N better than 100 on the strong emission lines. At mid latitudes, the spectral range display several features, originating from different atmospheric layers:

1) The solar reflected component at 3.52 \mum is strongly modulated by CH4 absorption in the Jovian atmosphere. The spatial variation of this feature is related to the altitude of the upper clouds, with mainly a band/zone modulation and the structure of the GRS.

2) At 3.33 \mum, the upper stratosphere is sounded from the CH4 fluorescence emission, in the hot band \nu3+\nu4-\nu4. This emission is detected here for the first time on Jupiter from the ground, in the wing of the strong telluric absorption of the \nu3 band.

3) The ionosphere is mapped from H3+ emission at all latitudes. This emission exhibits strong longitudinal variations, as first mapped by Miller {\em et al.} (Icarus, 1997). \\ Cylindrical maps for these three atmospheric layers give a tomography of the Jovian atmosphere from the lower stratosphere up to the ionosphere, at a spatial resolution of roughly 1 arcsec. These observations are a ground based counterpart of the infrared observations by Cassini and Galileo recorded during the same period.

{\em This work is based on observations collected at the European Southern Observatory, Paranal, Chile (ESO program 66.C-0070)}

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