H3 + measurements in the Jovian atmosphere with JIRAM/Juno

The NASA Juno mission has been investigating Jupiter's atmosphere since August 2016, providing unprecedented insight on the atmosphere of the planet. The Jupiter Infrared Auroral Mapper (JIRAM) experiment, on board Juno, performed spectroscopic observations of the H3+ emissions both in the auroral regions (Dinelli et al., 2017; Adriani et al.,2017; Mura et al., 2017) and at mid latitudes. In the present work, we concentrate on the observations acquired by the JIRAM spectrometer during the first Jupiter passage on 26-27 August 2016, when the spacecraft was at about 500,000-1,200,000 km from the planet. During a portion of the observations, the slit of the spectrometer was sampling Jupiter's limb in the latitude range from 30 to 60 deg for both hemispheres. In the 3-4 ?m spectral region, the limb spectra show the typical features of the H3+ emission, usually used to retrieve concentration and temperature of this species in the auroral region. In this work we exploit this spectral region to provide new insight on the H3+ vertical distribution and, more generally, on thecomposition of the atmosphere of Jupiter. The spatial resolution of the limb observations of Jupiter, ranging between 50 and 130 km, is favourable for investigating the vertical distribution of H3+. The vertical profiles of the integrated H3+ intensity will be presented along with the preliminary results of the retrieval of the H3+ vertical volume mixing ratio (VMR) distribution and compared with predictions from available atmospheric models of the planet (Achilleos et al. 1998). Possible variability of the altitude distribution of the peak emission with respect to latitude and longitude will also be discussed.