Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001apj...559l.183g&link_type=abstract
The Astrophysical Journal, Volume 559, Issue 2, pp. L183-L183.
Astronomy and Astrophysics
Astrophysics
24
Scientific paper
In the Letter ``Enrichments in Volatiles in Jupiter: A New Interpretation of the Galileo Measurements'' by D. Gautier, F. Hersant, O. Mousis, and J. I. Lunine (ApJ, 550, L227 [2001]), the authors have revised their calculations of the curves of stability of clathrate hydrates of H2S, Xe, CH4, Kr, CO, N2, and Ar. This reanalysis was prompted by the fact that the authors realized that, except for the NH3-H2O hydrate, the temperature had been calculated as a function of the total pressure, neglecting the mixing ratio of each species. When taking this into account, the clathration temperature as a function of the total pressure is somewhat lower. Revised calculations, shown in Figure 1, have been done for a solar composition of all considered elements and assuming CO/CH4=5 and N2/NH3=10. The main differences with the previous calculations are that the Xe clathrate curve is now located on the T-P diagram below that of CH4 and the Kr curve is located below that of N2. In addition, the clathration at 5.2 AU occurred later in the history of the nebula than previously calculated. Clathrations of H2S, NH3, CH4, Xe, CO, N2, Kr, and Ar occur now at t=0.83, 0.85, 1.22, 1.24, 1.56, 1.65, 1.80, and 2.04 Myr respectively. The calculations of the resulting enrichments in Jupiter are shown in Figure 2. They have been calibrated on the central value of Kr (almost equal to that of Ar), resulting in a total width of the feeding zone of Jupiter centered at 5.2 AU equal to 4.46 AU and in a collapse of the hydrogen envelope of the planet occurring 5.85×106 yr after the formation of the Sun. The calculated Xe enrichment is slightly higher than the upper limit of the observed one, but should the calculation be calibrated on the lower limit of Ar or Kr, it would be easily within the error bars of the Xe measurements. The fit of the calculated C enrichment to the measurements is better than in the original Letter (Gautier et al. 2001). Interestingly enough, the calculated N enrichment when all nitrogen is assumed to be in the form of N2 in the solar nebula is now compatible with the observed enrichment. The calculated value when all nitrogen is assumed to be in the form of NH3 is slightly above the upper limit of the observed N enrichment, but this assumption is in conflict with predictions of the models of composition of the nebula. All N2/NH3 ratios higher than 10 are consistent with observations. The discrepancy between the calculated S enrichment and the observation is the same as in Gautier et al. (2001). The predicted O/H enrichment is at least 9.4 times solar, requiring an H2O/H2 ratio in the nebula at 5 AU, when water condenses, to be at least 2.5 times (O/H) solar. In summary, the reanalysis of the calculations of Gautier et al. (2001) does not change the conclusions developed in their article. The main changes are that the N enrichment is now easily explained for a high N2/NH3 ratio and that Jupiter is completed at t=5.85×106 yr. Moreover, it is no longer necessary to assume that some N was trapped in organics in the feeding zone of Jupiter.
Gautier Daniel
Hersant Franck
Lunine Jonathan I.
Mousis Oliver
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