Abstract
We investigate the thermal equation of state, bulk modulus, thermal expansion coefficient, and heat capacity of MH-III (CH4 filled-ice Ih), needed for the study of CH4 transport and outgassing for the case of Titan and superTitans. We employ density functional theory and ab initio molecular dynamics simulations in the generalizedgradient approximation with a van der Waals functional. We examine the temperature range 300-500 K and pressures between 2 and 7 GPa. We find that in this P-T range MH-III is less dense than liquid water. There is uncertainty in the normalized moment of inertia (MOI) of Titan;it is estimated to be in the range of 0.33-0.34. If Titan's MOI is 0.34, MH-III is not stable at present in Titan's interior, yielding an easier path for the outgassing of CH4. However, for an MOI of 0.33, MH-III is thermodynamically stable at the bottom of an ice-rock internal layer capable of storing CH4. For rock mass fractions less than or similar to 0.2 upwelling melt is likely hot enough to dissociate MH-III along its path. For super-Titans considering a mixture of MH-III and ice VII, melt is always positively buoyant if the H2O:CH4 mole fraction is >5.5. Our thermal evolution model shows that MH-III may be present today in Titan's core, confined to a thin (approximate to 10 km) outer shell. We find that the heat capacity of MH-III is higher than measured values for pure water ice, larger than heat capacity often adopted for ice-rock mixtures with implications for internal heating.
| Dokumententyp: | Zeitschriftenartikel |
|---|---|
| Fakultät: | Geowissenschaften > Department für Geo- und Umweltwissenschaften |
| Themengebiete: | 500 Naturwissenschaften und Mathematik > 550 Geowissenschaften, Geologie |
| ISSN: | 0004-637X |
| Sprache: | Englisch |
| Dokumenten ID: | 84017 |
| Datum der Veröffentlichung auf Open Access LMU: | 15. Dez. 2021, 15:10 |
| Letzte Änderungen: | 15. Dez. 2021, 15:10 |
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