U. Von Zahn et al., Helium in Jupiter's atmosphere: Results from the Galileo probe Helium Interferometer Experiment, J GEO R-PLA, 103(E10), 1998, pp. 22815-22829
On December 7, 1995, the NASA Galileo probe provided the first in situ meas
urements of the helium abundance in the atmosphere of Jupiter. Our Jamin in
terferometer measured precisely the refractive index of the Jovian atmosphe
re in the pressure region from 2 to 12 bars. From these measurements, we de
rive the atmospheric helium mole fraction to be 0.1359 +/- 0.0027. The corr
esponding helium mass fraction matches closely, but accidentally, the curre
nt helium abundance of the atmosphere of the Sun. However, both the Jovian
and the solar value fall somewhat below the protosolar value. This suggests
that in both Jupiter and the Sun processes are active which separate heliu
m from hydrogen.