Tropospheric gas composition of Jupiter's north equatorial belt (NH3, PH3, CH3D, GeH4, H2O) and the Jovian D/H isotopic ratio

The gas composition of the troposphere of Jupiter in the clearest regions of the North Equatorial Belt (NEB) was derived from the Voyager 1 IRIS data. The infrared spectrum for this homogeneous ''cloud-free'' region was modeled to infer altitude profiles for NH3, PH3, CH3D, GeH4, and H2O. The profiles for NH3 and PH3 were found to be depleted in the upper troposphere but otherwise in agreement with their solar values at the 1 bar level. The mole fraction for CH3D was determined to be 3.5/sup +1.0//sub -1.3/ x 10-7. The GeH4 mole fraction of 7 +- 2 x 10-10 at the 2-5 bar level is a factor of 10 lower than the solar value. The H2O mole fraction is approx.1 x 10-6 at the 2.5 bar level and is increasing to approx.3 x 10-5 at 4 bars where it is a factor of 30 lower than solar. Using IRIS inferred values for the mole fractions of CH3D and CH4 a value of D/H = 3.6/sup +1.0//sub -1.4/ x 10-5 is derived. Assuming this Jovian D/H ratio is representative of the protosolar nebula, and correcting for chemical galactic evolution, yields a value of 5.5--9.0 x 10-5 for the primordial D/H ratio and an upper limit of 1.8--2.4 x 10-31 g cm-3 for the present-day baryon density