DETECTION OF (H2O)-O-18 IN JUPITER

We report the detection of a single line of (H2O)-O-18 in Jupiter at 1980.76 cm(-1), the first detection of O-18 in Jupiter. Models of the spectrum of Jupiter near this line imply that the Jovian isotopic abundance ratio O-18/O-16 is 1-3 times the terrestrial value. It is not possible to distinguish between the terrestrial ratio and highly anomalous oxygen isotope ratios of 2 or 3 times terrestrial because of the difficulties in modeling the spectrum and our reliance on a single (H2O)-O-18 feature. Anomalous O-18 in Jupiter could be caused by an intrinsic oxygen-isotope heterogeneity between solid and gaseous reservoirs in the preplanetary nebula, although given the constancy of O-16/O-18 in other solar system objects, such an explanation seems unlikely. Neither the isotopic anomalies in individual meteorite grains nor the differences in isotopic ratios between those in the solar system and in the interstellar medium would explain a gross enhancement of O-18 in the outer solar system. The Galileo Probe Mass Spectrometer experiment may not allow a more accurate abundance determination of (H2O)-O-18 because of the much larger amount of interfering Ne-20 that may be present. It appears that no lines of (H2O)-O-17 are detectable in the 5 mu m window.