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 limbBo

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d et

al.,

200

9Va

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t al.,

199

9

Main emissionVisible250 km

Io footprint tailFar-UV900 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

Bonf

ond

et a

l., a

ccep

ted

Peak altitude

Mean peak altitude: 400 km Higher than the 250 km

observed by Galileo

Bonf

ond

et a

l., a

ccep

ted

Fit of the brightness profile as a function of the electron energy distribution

MonoenergeticMaxwellianKappa

Bonfond et al., accepted

Hydrocarbon absorption

The peak altitude is strangely close to the methane homopauseTwo distributions peaking at different altitudes lead to similar observed profiles

Bonf

ond

et a

l., a

ccep

ted

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.

Bonf

ond

et a

l., a

ccep

ted

Peak shift in the spectra

15 spectral observationsMean shift: 90 km

Significant absorptionBonf

ond

et a

l., a

ccep

ted

Yet, two possibilities

Brightness

Altit

ude

400 km250 km

400 km400 km

ObservedObserved Emitted Emitted

Auroral curtain in the limb plane Auroral curtain behind the limb plane

Conclusions

The apparent brightness peak is at 400 km BUT CH4 absorption could explain such a profile BUT the color ratio is weak at the limb BUT C2H2 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.