Composition and origin of the atmosphere of Jupiter - an update, and implications for the extrasolar giant planets

New developments have led to this update of the composition and origin of Jupiter's atmosphere that were originally discussed in our Planet. Space Sci. 47 (1999) 1243 paper. Since Jupiter can provide important insight into the atmospheres of extrasolar giant planets (EGP), we also discuss here the possible implications of the first detection of an atmosphere on an EGP. The ammonia mixing ratio on Jupiter has now been determined directly from the Galileo probe mass spectrometer (GPMS) data, and its value relative to H-2 (7.1 +/- 3.2) x 10(-4) in the 9-12 bar region, is found to be similar to the previously reported result inferred from the radio attenuation technique on Galileo. The Jovian N-15/N-14 ratio is found to be much lower than the terrestrial value at (2.3 +/- 0.3) x 10(-3). A complete analysis of the various uncertainties in the GPMS data yields an H2O mixing ratio of 6.0(+3.9,-2.8) x 10(-4) at 19 bar in the hotspot, and a trend of increase with depth; all other mixing ratios and error bars remain unchanged. CH3, previously detected on Saturn and Neptune, has now also been detected in the atmosphere of Jupiter recently by Cassini. Benzene is the heaviest hydrocarbon detected to date in the atmospheres of Jupiter and Saturn. Abundances inferred from Infrared Space Observatory measurements are 9(+4.5,-7.5) x 10(14) and 4.7(+2.1, -1.1) X 10(13) cm(-2) for pressures less than 50 and 10 mbar on Jupiter and Saturn, respectively. Finally, we propose that the recently detected sodium in the atmosphere of the EGP orbiting HD 209458 may have mainly a post-accretionary extraplanetary origin, rather than being primordial. (C) 2002 Elsevier Science Ltd. All rights reserved.