HST spectro-imaging of Jupiter's aurorae with FOC and GHRS, in relation with Galileo in-situ measurements
L. Pallier, R. Prangé (IAS, France), D. Rego (UCL, UK), J.E.P. Connerney (NASA/GSFC), P. Zarka (Observatoire de Meudon,France), L. Frank (University of Iowa), M. Kivelson (UCLA), D. Southwood (Imperial College, UK)
High latitude particle precipitation from the magnetosphere
causes collisional excitation of the major atmospheric constituents,
H and H 
, and gives rise to FUV auroral emissions. The auroral
pattern is the 2-D projection of active regions in the magnetosphere
along magnetic field lines. By contrast, the spectral characteristics
of the emission bear the signature of the precipitating particles and of
the auroral atmospheric structure.
High spatial resolution images of the FUV Jovian aurorae in the H
Lyman bands near 1550 
obtained with the HST Faint Object
Camera in July 1994 and September 1996 allow to identification of
specific auroral features at various latitudes and longitudes,
magnetically connected to different regions in the Jovian
magnetosphere. In particular, the surface footprint of Io and the
"main oval" can be tested against various magnetic field models, and
provide constraints on the internal and external
(magnetodisc?) components of the field, respectively.
GHRS spectra of the H Lyman 
line and of the H Lyman
and Werner bands at various spectral resolution taken at the magnetic
footprint of Galileo, show differences
in the spectral diagnostic obtained in each of these regions. Evidence
of dramatic precipitation-induced disturbances in the upper atmosphere
is inferred.
Temporal variations of the global and local auroral activity will be discussed in the frame of the Galileo mission.