Preliminary Juno Microwave Radiometer measurements have confirmed observational constraints over the past two decades on Jupiter's O/H ratio, finding a modest supersolar enrichment. The Juno O/H ratio is consistent with supersolar enrichments of other volatile species previously measured by the Galileo Probe. Although the O/H ratio is an important cosmochemical constraint on the formation of Jupiter and planets in general, there is some uncertainty in the bulk planetary O/H ratio due to partitioning of heavy elements between the core and the envelope of the planet. An additional cosmochemical ratio, the C/O ratio, largely avoids the issue of core/envelope partitioning. Jupiter's C/O ratio renders it unlikely that the primary vehicle for heavy element enrichment of Jupiter was large planetesimals with water ice clathrate composition. Other processes, such as accretion of amorphous ice, non-water ices, disk photoevaporation, and Bondi-Hoyle accretion are more plausible ways for Jupiter to have formed with the observed C/O, C/H, and O/H ratios. However, the wide range of chemical modification processes at work in the giant planet formation era means that firm conclusions regarding the planet's formation history require much more data. Specifically, the full composition (envelope and core) of all four giant planets must be measured to decode the cosmochemical markers of planet formation.
Speaker: Mike Wong, UC Berkeley
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