Other
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p12c..06s&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P12C-06
Other
3630 Experimental Mineralogy And Petrology, 3672 Planetary Mineralogy And Petrology (5410), 5430 Interiors (8147), 6218 Jovian Satellites
Scientific paper
We have conducted a series of experiments designed to simulate chemical processes within large icy satellites. Few phase equilibria data exist which are relevant to the chemical evolution of moons such as Jupiter's Europa and Ganymede, Saturn's Titan and Neptune's Triton; however, models of their interiors are critically dependent on their internal chemistry and density. An internally generated magnetic field has been observed for Ganymede which implies the existence of a liquid metallic core, and accordingly an interior temperature exceeding 1000ṡC. This observation, coupled with the known abundance of water ice on Ganymede, suggests that rock - water interactions at high temperatures and pressures (prospectively in the past) would control the interior mineralogy of these satellites. Additionally, organic material has been observed on the surface of Ganymede, and in conjunction with the large complement of water ice, it has been suggested that icy satellites possess the prerequisites for life to originate; however, the stability of organic material under high-pressure hydrothermal processing is unclear. We used a piston-cylinder press to react material of carbonaceous chondrite chemistry with H2O at a range of temperatures and oxidation states at a pressure of 1.5 GPa, and make the following observations: 1) At temperatures below ~850ṡC the density of the rock interior will be largely that of hydrated ferromagnesian silicates (serpentine - chlorite - talc depending on temperature and oxidation state), 2) Iron and sulfur alloy readily under these conditions, forming the mineral pyrrhotite -- a metallic core of this chemistry is therefore likely, and 3) Hydrothermal processing of organic species of carbon at temperatures above 450ṡC produces carbonate minerals -- the prerequisite materials for life are not preserved deep within icy satellites. To further investigate the high-pressure hydrothermal processing of organic material we are conducting experiments that allow in situ observations on less complicated systems using a diamond anvil cell. We used Raman spectroscopy to examine the compression of nCH2-polyethylene (a simple polymerized alkane) in the presence of H2O at room temperature. Additionally, we have laser heated samples of polyethylene and polyethylene plus CaSiO3-wollastonite in the presence of H2O at pressures between 1 and 2.5 GPa. We observe the formation of graphite and methane in the polyethylene and water experiments with no evidence for the formation of either a clathrate or filled-ice structure. The addition of wollastonite causes the formation of carbonates: this is likely a result of an increased fO2 and supply of Ca.
Hemley Russell J.
Ryerson Frederick J.
Scott Henry P.
Williams Quentin
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