Vertical and local time variability in Jupiter's ionosphere

We present observations and modeling of the state of Jupiter’s non-auroral upper atmosphere surrounding Juno perijove 54. Juno radio occultations sampled Jupiter’s dawn ionosphere near 38N planetocentric latitude around 12 UTC on 7 September 2023. Simultaneous IR spectroscopy was obtained by JWST/NIRSpec, Keck/NIRSPEC, and IRTF/iSHELL. Analysis of IR spectra yields maps of H3+ density and temperature in altitude, latitude, longitude, and local time, providing spatiotemporal context for Juno PJ54 observations. Model reproductions of the measured diurnal variation of H3+ also provide key insight into unconstrained giant planet ionospheric chemistry (the conversion of H+ to H3+ by an intermediate reaction with vibrationally-excited H2). We find that Jupiter’s mid-latitude ionosphere during this epoch was reasonably well-behaved in comparison to the range of dynamic plasma distributions seen in prior giant planet observations. H3+ temperatures are roughly 700 K, densities a few thousand ions/cc, and loss rates for H+ + H2 reactions are line with prior estimates in the literature.

This work was supported by Keck Key Strategic Mission Support Grant 80NSSC22K0954, JWST-GO-03665.002-A, and NASA SSW Grant 80NSSC20K1045.