The helium abundance of Saturn from Voyager measurements

The helium abundance in the atmosphere of Saturn is obtained from Voyager measurements by two methods. The first method combines infrared spectra and vertical profiles derived from radio occultation measurements and yields a hydrogen mole fraction of q = 0.963 + or - 0.024 corresponding to a helium mass fraction of Y = 0.06 + or - 0.05. The estimated errors are primarily due to uncertainties in the radio occultation profile and in the abundance of methane, which contributes significantly to the mean molecular weight. The second method is based on the direct inversion of infrared spectra and yields values consistent with those from the first method; however, examination of the sensitivities of the two methods indicates that in the Saturnian case the first approach provides more accurate results. Comparison of the helium abundance of Saturn with that of Jupiter and the sun suggests that helium precipitation is significant in Saturn but may not have begun in Jupiter.