First Observations of CH 4 and H3+ Spatially Resolved Emission Layers at Jupiter Equator, as Seen by JIRAM/Juno

In this work, we present the detection of CH4 and H3+ emissions in the equatorial atmosphere ofJupiter as two well-separated layers located, respectively, at tangent altitudes of about 200 and 500-600 kmabove the 1-bar level using the observations of the Jovian InfraRed Auroral Mapper (JIRAM), on boardJuno. This provides details of the vertical distribution of H3+ retrieving its Volume Mixing Ratio (VMR),concentration, and temperature. The thermal profile obtained from H3+shows a peak of 600-800 K at about 550 km, with lower values than the ones reported in Seiff et al. (1998), https://doi.org/10.1029/98JE01766above 500 km using VMR and temperature as free parameters and above 650 km when VMR is kept fixed withthat model in the retrieval procedure. The observed deviations from the Galileo's profile could potentially pointto significant variability in the exospheric temperature with time. We suggest that vertically propagating wavesare the most likely explanation for the observed VMR and temperature variations in the JIRAM data. Otherpossible phenomena could explain the observed evidence, for example, dynamic activity driving chemicalspecies from lower layers toward the upper atmosphere, like the advection-diffusion processes, or precipitationby soft electrons, although better modeling is required to test these hypothesis. The characterization of CH4 and H3+ species, simultaneously observed by JIRAM, offers the opportunity for better constraining atmospheric models of Jupiter at equatorial latitudes.