THE GALILEO PROBE MASS-SPECTROMETER - COMPOSITION OF JUPITER ATMOSPHERE

The composition of the jovian atmosphere from 0.5 to 21 bars along the descent trajectory was determined by a quadrupole mass spectrometer o n the Galileo probe. The mixing ratio of He (helium) to H-2 (hydrogen) , 0.156, is close to the solar ratio. The abundances of methane, water , argon, neon, and hydrogen sulfide were measured; krypton and xenon w ere detected. As measured in the jovian atmosphere, the amount of carb on is 2.9 times the solar abundance relative to H-2, the amount of sul fur is greater than the solar abundance, and the amount of oxygen is m uch less than the solar abundance. The neon abundance compared with th at of hydrogen is about an order of magnitude less than the solar abun dance. Isotopic ratios of carbon and the noble gases are consistent wi th solar values. The measured ratio of deuterium to hydrogen (D/H) of (5 +/- 2) x 10(-5) indicates that this ratio is greater in solar-syste m hydrogen than in local interstellar hydrogen, and the He-3/He-4 rati o of (1.1 +/- 0.2) x 10(-4) provides a new value for protosolar (solar nebula) helium isotopes. Together, the D/H and He-3/He-4 ratios are c onsistent with conversion in the sun of protosolar deuterium to presen t-day He-3.