Deciphering the composition of Jupiter’s building blocks from Juno water measurements

The recent water and ammonia measurements (Bolton et al. 2017; Li et al. 2017, 2020) performed at 100 bars or more by the Juno microwave radiometer in the interior of Jupiter are combined with the data previously acquired by the Galileo probe (Mahaffy et al. 2000; Wong et al. 2004) and the Cassini spacecraft (Fletcher et al. 2009) to derive hints on the composition of solids vaporized in the envelope of the forming Jupiter during its growth.

To do so, we computed the condensation sequence of the ices of astrophysical interest forming in the feeding zone of the growing Jupiter by using the equilibrium curves of pure condensates and various clathrates derived from compilations of laboratory data or fits from models calibrated on experiments. The employed disk model detailing the evolution of temperature and pressure at the location of Jupiter is derived from Aguichine et al. (2020). Our approach allows i) the computation of the composition of ices forming in feeding zone of Jupiter, and ii) the determination of the amount of these solids needed in the giant planet’s envelope to match the measured volatiles enrichments. The Juno water measurement is used to calibrate our model.

Figure 1 represents an example of volatiles enrichments in Jupiter fitted with our planetesimal composition model. In this case, we assume that the abundances of volatiles are protosolar and that only pure ices formed in the protosolar nebula. The figure shows that all species abundances, except that of argon, can be matched in Jupiter. The corresponding amount of ices vaporized in the envelope ranges between 3.9 and 20.7 Earth-masses. Other cases, with increasing water abundance in the protosolar nebula and the presence of clathrates, are currently investigated.

Fig. 1.Ratio of Jovian to protosolar abundances in the case the volatiles part of the building blocks is formed from pure condensates only.

 

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