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 Ganymede Titan Ganymede and Titan: пѓ�are the two largest satellites in the Solar System; пѓ�were formed in the outer zones of their central planets (Jupiter and Saturn); пѓ�are regular satellites (their orbits and rotation are the same as the rotation of associated central planets); пѓ� satellites rotation is synchronous with their orbits; пѓ� low density of the satellites suggests that they could contain remarkable amounts of H2O. The main differences between Ganymede and Titan "Galileo", "Voyager" and "Cassini-Huygens" spacecraft missions to Jupiter and Saturn showed that Ganymede and Titan are different both external and internally: Ganymede Titan Atmosphere пѓ� Trace oxygen atmosphere Dense nitrogen atmosphere (~400 km): вЂ“ N2 - 98.4%, CH4 and Ar - 1.6%, вЂ“ CO2 and other trace organics. вЂ“ Free oxygen is absent. Magnetic field пѓ� A relatively strong intrinsic magnetic field and magnetosphere. Intrinsic magnetic field is absent. Climate пѓ� Exogenous climatic processes (evaporation, condensation, precipitation, cycle of substances, seasons) are not available. The seasonal weather patterns are similar to Earth, but governed by methane cycle (including winds, rains, seasons change, etc.). Surface features Two types of terrain: вЂ“ Very old, highly cratered, dark regions; вЂ“ Younger (but still ancient), lighter regions marked with an extensive array of grooves and ridges; Criovolcanism insignificant but important in the formation of the bright terrain. The surface is "complex, fluid-processed, and geologically young" (c): вЂ“ Ridges, valleys, riverbeds, dunes, stable lakes of liquid hydrocarbons; вЂ“ Minor amounts of relatively young impact craters; вЂ“ Clearly defined criovolcanism. Models of Ganymede and Titan. Titan: Ganymede: Mitri et al., 2009 Sohl F. et al., 2003 Grasset et al., 2005 GanymedeвЂ™s general image from NASA, JPL Sohl F., 2010 TitanвЂ™s general image from NASA Phase diagram of water and the temperature distribution in the GanymedeвЂ™s and TitanвЂ™s icy crust. 325 T, K 50 50 300 100 150 250 200 300 350 400 450 500 H , km 25 L T ,o C 275 0 250 III V Ih 225 200 175 150 125 100 75 550 II VI H I h = 8 0 k m -2 5 H L= 310 k m -5 0 H Ih = 95 k m H L= 230 k m -7 5 H Ih = 1 5 0 -1 6 0 k m -1 0 0 ( m o d e ls w it h o u t in t e r n a l o c e a n ) -1 2 5 -1 5 0 Straight thin lines - conductive temperature profiles through the G a n y m e d e 's external (ice-Ih) crust. s u r f a c e c o n d it io n s s -1 7 T ita n 's Dashed lines вЂ“ adiabatic convective heat transfer in5 the water subcrustal ocean and in high-pressure ices. H, HIh, HL - the distance from the satellite's surface (depth), the P, kb 2 4 thickness of the6 external ice-Ih crust 8 and of the inner 1 0liquid ocean respectively. Calculation of the Ganymede's and TitanвЂ™s heat flux F(mW/m2) = [пЃЈo(RSat - РќIh) /(Рќ Ih RSat)]ln[T2 /Рў1] F ,m W /m 2 400 20 350 300 250 200 150 100 50 0 пЃЈo = 567 W/m - thermal conductivity of ice Ih, H w, km RSat вЂ“ satelliteвЂ™s radius, 15 РќIh вЂ“ thickness of the icy crust, Рў1 вЂ“ satellite's surface temperature, M e lt in g p o in ts L - I h 10 T r ip le p o in t F = 7 m W /m 2 [ 2 ] 5 F = 3 .3 m W /m 2 L -Ih -III 2 5 1 .1 5 K / 2 .0 7 k b a r F = 5 m W /m 2 [ 1 ] Рў2 вЂ“ the temperature at the ice-Ih liquid phase boundary, Hw - the thickness of internal ocean, F вЂ“ heat flux. F = 2 .9 m W /m 2 0 20 40 60 80 100 120 140 160 ГЌ Ih , k m 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.  Bland, M.T., et al., 2009  Mitri G., Showman A., 2008 Initinal data for modeling, problem setting and methods of solution Physical characteristics of the satellites Ganymede Titan Pressure at the surface, P[bar] 1.0e-06 1.467 Temperature at the surface, T [K] 110.0 93.0 Gravity acceleration, g пЂЁ R пЂ© [m/s2]; 1.428 1.35486 Radius, R [km] 2634.0 2575.0 Average density, g/cm3 1.936 1.88202 Mass, M [kg] 0.14819e24 0.1346e24 Normalized moment of inertia, I/MR2 0.3105 0.3419 Models of the satellites internal structure described by the system of following equations: пѓ� Equations of hydrostatic equilibrium: dP dR пЂЅ пЂ пЃІ пЂЁR пЂ© пѓ— g пЂЁR пЂ© , dg dR пЂЅ пЂ 4пЃ° пѓ— G пѓ— пЃІ пЂЁ R пЂ© пЂ 2 g пЂЁ R пЂ© R пѓ� The equations of the satellites mass and moment of inertia: n n 4 3 3 8 5 5 I пЂЅ пЃ° пѓҐ пЃІ R i пЂ R i пЂ«1 , M пЂЅ пЃ° пѓҐ пЃІ R i пЂ R i пЂ«1 i i 3 15 пЂЁ пЂЁ пЂ© iпЂЅ0 пЂ© iпЂЅ0 пЃІ пЂЁ R пЂ© п‚§ density of the water-ice shell, пЃІ ice , m пЃІ Fe пЂ Si пѓ� The equation for calculating ice component concentration in mantle: C ice пЂЅ пЃІ ice , m пЂЁ пЃІ Fe пЂ Si пЂ пЃІ m пЂ© пЃІ m пЂЁ пЃІ Fe пЂ Si пЂ пЃІ ice , m пЂ© пЃІ Fe пЂ Si = 3.15 - 3.62 g/cm3 (LL-chondrites) пѓ�High-pressure water ices equations of state. пЃІm п‚§ average density of ice in mantle, п‚§ density of the rockвЂ“iron component, п‚§ average density of mantle G a n y m e d e 's s u r fa c e 2500 Ih (~ 95 km ) ~230 km V (~ 55 km ) liq u id o c e a n ~465 km ~530 km VI 1500 пЃІ c o re = 5.1 5 g /c m 3 F e -S i m a n tle пЃІ c o re = 5.7 g /c m 3 пЃІ co re = 6 .5 g /c m 3 500 F e -F e S c o r e 820 840 860 880 900 0 .3 8 8 0 .3 9 2 0 .3 9 6 I /M R 2 fo r r o c k вЂ“ ir o n c o r e 3 .5 3 .5 5 3 .6 3 .6 5 M a n tle d e n sity , g /c m 3 T it a n 's s u r f a c e 2500 Ih (8 0 k m ) liq u id o c e a n ( ~ 3 1 0 k m ) V + V I (~ 1 2 0 k m ) 1500 r o c k - ic e m a n t le 500 r o c k - ir o n c o r e 400 440 480 520 T h ic k n e s s o f th e w a te r -ic y s h e ll, k m T h ic k n e s s o f th e w a te r -ic y sh e ll, k m 0 .3 8 4 D is ta n c e fr o m T ita n 's c e n t e r , k m D is t a n c e f r o m G a n im e d e 's c e n te r , k m The internal structure of Ganymede and Titan. 0 .4 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 a ) 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. Water content and density gradients in large icy satellites of Jupiter and Saturn. 3 .6 60 Io 3 .2 G anym ede E u ro p a C a llis to H 2O , w t % d e n s ity , g /c m 3 T ita n 40 20 2 .8 2 .4 T ita n G anym ede 2 C a llis to E u ro p a Io 1 .6 0 5 10 15 20 25 O rb ital d istan ce (in R p lan et ) 30 5 10 15 20 25 O rb ital d istan ce (in R p lan et ) The total water content in Ganymede is 46-48% , in Titan - 45-52% . 30 Conclusion. п‚§Ganymede and Titan are the similar in size and chemical composition: the density of the satellitesвЂ™ rock material is typical for the hydrated L/LL chondrites. п‚§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). п‚§Ganymede and Titan both may have subsurface oceans. вЂ“ Internal ocean in the satellites not forms when the heat fluxes less than 3.3 mW/m2 and 2.9 mW/m2 for Titan and Ganymede respectively. п‚§Internal structure of the satellites can differ fundamentally: вЂ“ 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. вЂ“ Titan is differentiated only partially: its inner areas are represented by a mixture of rock and ice components. п‚§ Equal content of bulk H2O and the same density of the satellitesвЂ™ 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/LLchondrites. Different conditions of the satellitesвЂ™ formation from accretion disks led to major differences in their internal structure.