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C. Emerich (IAS-Orsay & IAP-Paris), L. Ben Jaffel (IAP-Paris), J.T. Clarke (Boston University), Y. Kim (Michigan University), G.E. Ballester (LPL-Arizona University), R. Prangé (IAS-Orsay), J. Sommeria (ENS-Lyon ), Institut d'Astrophysique Spatiale Team, Institut d'Astrophysique de Paris Team
H Ly-\alpha observations of Jupiter by the HST-STIS instrument were repeated not far from the 2000 opposition. This opportunity was taken to check the serendipitous findings presented during last DPS, concerning the detection of hot atomic H in the upper Jovian atmosphere.
The STIS spectro-imager, associated with the long aperture (52 \arcsec \times 0.5 \arcsec), provided accurate measurements of the Jovian Ly-\alpha line profiles in different locations of the planetary disc.
These new observations confirm the existence of dissymmetries on the H-Ly-\alpha Jovian spectra measured near the limbs: the red wing flux is in excess relative to the blue one for the receding limb, the reverse holding for the approaching limb.
The observed dissymmetries, particularly apparent around the limbs, are interpreted as the signature of hot Hydrogen atoms propagating in the the upper Jovian atmosphere, with a velocity distribution in excess relative to the planetary rotation and roughly centered at 60 km/s.
Both series of observations being separated by about 14 months, the physical processes at the origin of the observed phenomenon appear to be permanent.
Some possible explanations are suggested.