Noble gas abundance and isotope ratios in the atmosphere of Jupiter from the Galileo Probe Mass Spectrometer

The Galileo Probe Mass Spectrometer provided the first data on the noble ga s mixing and isotope ratios in the Jovian atmosphere. These measurements an d the comparison with solar values constrain models of Jupiter's formation. Significant refinements to the initially reported abundances of argon, kry pton, and xenon have been enabled through post-encounter laboratory calibra tions using a refurbished engineering unit mass spectrometer nearly identic al to the flight unit. The abundances relative to hydrogen for argon, krypt on, and xenon are respectively 2.5 +/- 0.5, 2.7 +/- 0.5, and 2.6 +/- 0.5 ti mes the solar ratios. The mixing ratios of He and Ne found in these studies are consistent with previously reported values of 0.8 and 0.1 times solar respectively. The Jovian Ar-36/Ar-38 ratio is 5.6 +/- 0.25 and the Ne-20/Ne -22 ratio is 13 +/- 2, consistent with the solar values of 5.77 and 13.81, respectively, that are derived from lunar mineral grain analysis. The distr ibution of xenon isotopes at Jupiter also resembles the solar distribution.