Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p51b0449n&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #P51B-0449
Physics
0350 Pressure, Density, And Temperature, 1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 5410 Composition, 6062 Satellites, 6218 Jovian Satellites
Scientific paper
The internal structure and composition of large icy satellites of giant planets are very important topics in planetary sciences. Based on the observed data of CI chondrite materials, it has been expected that three-quarters of the volatiles are sulfates, and 73wt.% of aqueous sulfate is magnesium sulfate MgSO4 [Frederiksson et al. 1998]._@Recently, it has been considered that MgSO4 is the most abundant volatiles in the icy objects. In the brine of orgueil meteorites, 97wt.% are composed of MgSO4 and Na2SO4. Magnesium sulfate MgSO4, is the most important brine in CI chondrites. We need to investigate the phase relations of the sulfate-water system up to the pressure of 5GPa to discuss the phases expected in the deep icy mantle or, ice-rock mixed core in the large icy satellites such as Callisto. Kargel(1991) suggested that the quantity of MgSO4 in the model of icy objects is about 8-20wt.%, which is close to the eutectic composition at 0.1MPa, 17wt.% MgSO4. Therefore, we adopted his estimation for the present starting compositions, i.e., the compositions of 0-30wt.% MgSO4_@in the MgSO4-H2O system. We used a diamond anvil cell with external heating for the in situ optical observation. We used the ruby-fluorescene method [Mao et al. 1986] (the diameter of ruby grains is around 70μ m) to determine the pressure. The temperature measurement was made by using the K-type thermocouple which was contacted to the steel gasket of the DAC. We generated temperatures more than 600K at high pressure by this cell. Identification of the phases was made by using the X-ray diffractometer and Raman spectroscope. We have clarified the phase equilibrium in the MgSO4-H2O binary system at room temperature. An eutectic point locates 14wt.% of MgSO4 where high pressure ice (ice ØY), magnesium sulfate hepta-hydrate MgSO4\x9D7H2O, and fluid coexist at 1.99GPa at the room temperature. We investigated this MgSO4-H2O binary system up to 600K and 5GPa with using the diamond anvil cell. At high pressure, we recognized MgSO4\x9D7H2O phase and some high pressure ices (IceØY, IceØZ) above 293K. Thus, we have the conclusions that a deep liquid ocean with the bottom pressure exceeding 1GPa must exist if MgSO4 content exceeds more than 10wt.%. The sediment composed of MgSO4\x9D7H2O phase might exist in the bottom of the ocean.
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