a1 Department of Astronomy, Cornell University, 402 Space Sciences Building, Ithaca, NY 14853 USA email: firstname.lastname@example.org
The giant planets of our solar system contain a record of elemental and isotopic ratios of keen interest for what they tell us about the origin of the planets and in particular the volatile compositions of the solid phases. In situ measurements of the Jovian atmosphere performed by the Galileo Probe during its descent in 1995 demonstrate the unique value of such a record, but limited currently by the unknown abundance of oxygen in the interior of Jupiter–a gap planned to be filled by the Juno mission set to arrive at Jupiter in July of 2016. Our lack of knowledge of the oxygen abundance allows for a number of models for the Jovian interior with a range of C/O ratios. The implications for the origin of terrestrial water are briefly discussed. The complementary data sets for Saturn may be obtained by a series of very close, nearly polar orbits, at the end of the Cassini-Huygens mission in 2016-2017, and the proposed Saturn Probe. This set can only obtain what we have for Jupiter if the Saturn Probe mission carries a microwave radiometer.