The altitude of the FUV main auroral emissions at Jupiter B. BONFOND, J. GUSTIN, J.-C. GÉRARD, D. GRODENT, A. RADIOTI, B. PALMAERTS, S. V. BADMAN, K. K. KHURANA AND C. TAO

Altitude above the limb Bonfond et al., 2009 Vasavada et al., 1999 Main emission Visible 250 km Io footprint tail Far-UV 900 km What about the altitude of the main emission in the far-UV? Is it the same as the visible one?

ME curtain above the limb Bonfond et al., accepted

Peak altitude  Mean peak altitude: 400 km  Higher than the 250 km observed by Galileo Bonfond et al., accepted

Fit of the brightness profile as a function of the electron energy distribution Monoenergetic Maxwellian Kappa Bonfond et al., accepted

Hydrocarbon absorption The peak altitude is strangely close to the methane homopause Two distributions peaking at different altitudes lead to similar observed profiles Bonfond et al., accepted

Color ratio above the limb Gérard et al., 2014

Color ratio above the limb Because of the slit width, its inclination relative to the limb and C2H2 absorption, the color ratio remains low. Bonfond et al., accepted

Peak shift in the spectra 15 spectral observations Mean shift: 90 km  Significant absorption Bonfond et al., accepted

Yet, two possibilities Brightness Altitude 400 km 250 km 400 km Observed Emitted Auroral curtain in the limb planeAuroral curtain behind the limb plane

Conclusions  The apparent brightness peak is at 400 km  BUT CH 4 absorption could explain such a profile  BUT the color ratio is weak at the limb  BUT C 2 H 2 absorption + geometry can explain it  Spectra show an absorption signature nevertheless  BUT the location of the spectral slit is uncertain  400 km represents an upper limit, but our observations are compatible with an peak altitude of 250 km.