FAINT LUMINISCENT RING OVER THE SATURN'S POLAR HEXAGON

Springtime insolation is presently advancing across Saturn's North Polar Region. Early solar radiation scattered through the gaseous giant's atmosphere gives a unique opportunity to sound the atmospheric structure at its upper-troposphere/lower-stratosphere (UTLS) at high latitudes. Here we report the detection of a tenuous bright structure in Saturn's Northern polar cap in correspondence with the hexagon equator-ward boundary, observed by Cassini Visual and Infrared Mapping Spectrometer (VIMS) on June 2013. The structure is spectrally characterized by an anomalously enhanced intensity in the 3610-3730 nm wavelength range and near 2500 nm, pertaining to relatively low opacity windows between strong methane absorption bands. Our first results suggest that a strong forward scattering by tropospheric clouds, higher in respect to the surrounding cloud deck, can be responsible for the enhanced intensity of the feature. This can be consistent with the atmospheric dynamics associated to the jet stream embedded in the polar hexagon. Further investigations at higher spectral resolution are highly desirable to better assess the clouds vertical distribution and microphysics in this interesting region.