Spatial and spectral characteristics of the Jovian polar haze inferred from 2-μm Juno/JIRAM spectro-images

We have analyzed the 2-μm spectro-images of the polar haze of Jupiter, which were observed by the JIRAM/Juno between 2016 and 2021, to study the vertical and latitudinal distributions of the polar haze and its absorption and scattering properties. We construct 2-μm brightness maps of the polar haze by selecting specific spectral ranges where the haze spectral features are revealed. The constructed haze images show no distinctive structure above the 55^oN/S latitudes showing fairly uniform and symmetrical distribution around the poles. We find no traces of the recently discovered stratospheric polar jets seen at radio wavelengths (Cavalié et al., 2021), of the circumpolar waves seen in the UV and around 8900 Å (e.g., Vincent et al., 2000; Barrado-Izagirre et al., 2008), nor of the mid-IR hot/bright spots on these images. These non-detections indicate that the major polar haze layers are lower than the jets and the mid-IR bright spots, but possibly higher than the circumpolar waves, and the thermal radiation from the mid-IR hot spots is negligible at 2 μm. We construct synthetic spectra between 2.0 and 2.5 μm, compare them with the JIRAM polar spectra, and find that the 2-μm polar haze is mostly located between 3 and 40 mbar pressure levels, approximately consistent with the previous results of Kim et al. (1991b), and also the literature values. We attempt to derive the anisotropic scattering properties of the haze particles for scattering angles between 60^o and 120^o, which is the only available range. The derived anisotropy tends to be moderate, but we are unable to determine a definite anisotropy within the statistical error bars of the observed data. We also derive the haze optical depths and single scattering albedos between 2.0 and 2.5 μm. The derived spectral structure of the opacity is roughly similar to those of hydrocarbon and nitrile ices of Titan retrieved by Sim et al. (2013) suggesting similar chemical compositions and possibly similar formation scenarios for Jupiter's haze particles but excluding nitrile ices.