New Analysis of the Voyager UVS H Lyman-α Emission of Saturn

The limb to limb Lyman-α reflectivities observed with the Voyager UVS instruments during the fly-by of Saturn are reanalyzed using a revised H Lyman-α sensitivity for the Voyager 1 instrument. The new sensitivity reconciles the measured intensities to those of Voyager 2 and gives a coherent set of data. To fit the UV airglow observations, four sources are considered: (i) H resonance and H₂ Rayleigh scattering of solar Lyman-α radiation, (ii) the interplanetary Lyman-α radiation, (iii) a possible internal source of unknown origin, (iv) the possibility of atmospheric turbulence recently proposed to explain the Lyman-α bulge of Jupiter. The analysis supports neither a dominant collisional excitation source for the UV emissions nor the presence of strong atmospheric turbulence. The best fit, in terms of brightness but also in terms of shape of the limb to limb profile (that is to say independent on the absolute calibrations), is obtained for pure resonance and Rayleigh scattering of solar and interstellar wind line in an atmosphere enriched in atomic hydrogen up to three times the standard model. Influx of water from the rings of Saturn may provide a means for producing such enhanced H densities in the upper atmosphere.