title: The helium mass fraction in Jupiter's atmosphere.
abstract: On 7 December 1995, the NASA Galileo probe provided in situ measurements of the helium abundance in the atmosphere of Jupiter. A Jamin interferometer measured the refractive index of the jovian atmosphere in the pressure region from 2 to 14 bars. These measurements indicate that the atmospheric helium mole fraction is 0.136 +/- 0.004. The corresponding helium mass fraction is slightly below the presolar value, which suggests that separation of helium from hydrogen in Jupiter's interior is only in its early stages.
authors.affiliation: Institut für Atmosphärenphysik an der Universität Rostock, Kühlungsborn, Germany.
authors.forename: U
authors.initials: U
authors.lastname: von Zahn
authors.forename: D M
authors.initials: DM
authors.lastname: Hunten
mesh_terms: D001272:Atmosphere; D005118:Extraterrestrial Environment; D006371:Helium / Q000032:analysis*; D006859:Hydrogen / Q000032:analysis*; D007368:Interferometry; D018538:Jupiter; D012031:Refractometry
chemical_list: D006371:Helium; D006859:Hydrogen