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A COMPARISON OF INTERNAL STRUCTURE OF GANYMEDE AND TITAN.

A COMPARISON OF INTERNAL STRUCTURE OF GANYMEDE AND TITAN. Dunaeva A.N., Kronrod V.A., Kuskov O.L. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, Russia. Jupiter. Saturn. Ganymede. Titan. Ganymede and Titan :.

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A COMPARISON OF INTERNAL STRUCTURE OF GANYMEDE AND TITAN.

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  1. A COMPARISON OF INTERNAL STRUCTURE OF GANYMEDE AND TITAN. Dunaeva A.N., Kronrod V.A., Kuskov O.L. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, Russia

  2. Jupiter Saturn Ganymede Titan Ganymede and Titan: • are the two largest satellites in the Solar System; • were formed in the outer zones of their central planets (Jupiter and Saturn); • are regular satellites (their orbits and rotation are the same as the rotation of associated central planets); • satellites rotation is synchronous with their orbits; • low density of the satellites suggests that they could contain remarkable amounts of H2O.

  3. The main differences between Ganymede andTitan "Galileo", "Voyager" and "Cassini-Huygens" spacecraft missions to Jupiter and Saturn showed that Ganymede and Titan are different both external and internally:

  4. Models of Ganymede and Titan. Titan: Ganymede: Mitri et al., 2009 Grasset et al., 2005 Sohl F. et al., 2003 Ganymede’s general image from NASA, JPL Sohl F., 2010 Titan’s general image from NASA

  5. Phase diagram of water and the temperature distribution in the Ganymede’s and Titan’s icy crust. Straight thin lines - conductive temperature profiles through the external (ice-Ih) crust. Dashed lines – adiabatic convective heat transfer in the water subcrustal ocean and in high-pressure ices. H, HIh, HL - the distance from the satellite's surface (depth), the thickness of the external ice-Ih crust and of the inner liquid ocean respectively.

  6. Calculation of the Ganymede's and Titan’s heat flux F(mW/m2) = [o(RSat - НIh) /(Н Ih RSat)]ln[T2 /Т1] o= 567 W/m - thermal conductivity of ice Ih, RSat – satellite’s radius, НIh – thickness of the icy crust, Т1 – satellite's surface temperature, Т2 – the temperature at the ice-Ih - liquid phase boundary, Hw - the thickness of internal ocean, F – heat flux. The thickness of the icy crust and internal ocean of Ganymede (blue) and Titan (black) via the heat flow through the satellites ice-Ih crust. [1] Bland, M.T., et al., 2009 [2] Mitri G., Showman A., 2008

  7. Initinal data for modeling, problem setting and methods of solution • Models of the satellites internal structure described by the system of following equations: • Equations of hydrostatic equilibrium: , • The equations of the satellites mass and moment of inertia: , • The equation for calculating ice component concentration in mantle: • High-pressure water ices equations of state. • density of the water-ice shell, • average density of ice in mantle, • density of the rock–iron component, • average density ofmantle = 3.15 - 3.62 g/cm3 (LL-chondrites)

  8. The internal structure of Ganymede and Titan. In general three-layer models of satellites including the outer water-ice shell, mantle (rock or rock-ice) and the inner core (Fe-Si or Fe-FeS) can be made. Moreover, two-layer models (without inner core) could be realized. In this case satellite has significant large outer water-icy shell, but its inner core not forms. On this model the maximum possible thickness of the water-ice shell is about 900 km and 500 km for Ganymede and Titan respectively.

  9. Water content and density gradients in large icy satellites of Jupiter and Saturn. The total water content in Ganymede is 46-48%, in Titan - 45-52%.

  10. Conclusion. • Ganymede and Titan are the similar in size and chemical composition: the density of the satellites’ rock material is typicalforthe hydrated L/LL chondrites. • The satellites do not differ in terms of bulk water content which in average is about 50 wt.% (water/rock ratio is close to 1). • Ganymede and Titan both may have subsurface oceans. • Internal ocean in the satellites not formswhentheheat fluxes less than 3.3 mW/m2and 2.9 mW/m2 for Titan and Ganymede respectively. • Internal structure of the satellites can differ fundamentally: • Ganymede is a completely differentiated body, with the inner region formed by separating of the original L/LL-chondritic substance into the silicate mantle and metallic core. • Titan is differentiated only partially: its inner areas are represented by a mixture of rock and ice components. • Equal content of bulk H2O and the same density of the satellites’ rock material allow to have assumption that Ganymede and Titan could have been formed from the planetesimals with similar composition corresponding to the ordinary L/LL-chondrites. Different conditions of the satellites’ formation from accretion disks led to major differences in their internal structure.

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