Galileo probe measurements of D/H and 3He/4He in Jupiter's atmosphere

The Galileo Probe Mass Spectrometer measurements in the atmosphere of Jupiter give D/H = (2.6 +/- 0.7) x 10(-5) He-3/He-4 = (1.66 +/- 0.05) x 10(-4) These ratios supercede earlier results by Niemann et al. (1996) and are based on a reevaluation of the instrument response at high count rates and a more detailed study of the contributions of different species to the mass peak at 3 amu. The D/H ratio is consistent with Voyager and ground based data and recent spectroscopic and solar wind (SW) values obtained from the Infrared Spectroscopic Observatory (1SO) and Ulysses. The He-3/He-4 ratio is higher than that found in meteoritic gases (1.5 +/- 0.3) x 10(-4). The Galileo result for D/H when compared with that for hydrogen in the local interstellar medium (1.6 +/- 0.12) x 10(-5) implies a small decrease in D/H in this part of the universe during the past 4.55 billion years. Thus, it tends to support small values of primordial D/H - in the range of several times 10(-5) rather than several times 10(-4). These results are also quite consistent with no change in (D + He-3)/H during the past 4.55 billion years in this part of our galaxy.