Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p22c0408b&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P22C-0408
Physics
5450 Orbital And Rotational Dynamics, 5455 Origin And Evolution, 5744 Orbital And Rotational Dynamics, 5749 Origin And Evolution, 6207 Comparative Planetology, 6020 Ice, 6045 Physics And Chemistry Of Materials
Scientific paper
Several papers have recently suggested that decomposition of gas hydrates could have played an important role in the geologic history of Mars and Europa. Gas hydrates form in porous sediments under low temperatures and high pressures. The FREZCHEM model was developed to predict chemical equilibria over the temperature range from -70 to +25 °C at 1 atm pressure using the Pitzer equations, which are valid to high ionic strengths. As currently structured, the FREZCHEM model lacks a pressure dependence and gas hydrate chemistry. The objectives of this paper were to (1) add a pressure dependence to the FREZCHEM model as a prelude to incorporating gas hydrate chemistry, and (2) use the model to examine the controversial subject of ice compressibility. Incorporation of pressure as a driver into the model necessitated a consideration of volumetric properties such as partial molal volumes (volume/mole) or its inverse, density (weight/volume). For the gas hydrate model, key variables and constants that were quantified as functions of pressure and temperature were solubility products, gas solubilities, activity coefficients, the density of aqueous solutions, and the activity of water. As an example of how pressure affects equilibria, even at a modest pressure of 100 bars, the solubility of gases was increased by about 17%; at 1000 bars, there was about a 400% increase in gas solubility. We used our model and experimental measurements of the freezing points of ice as a function of pressure to estimate the compressibility of ice (Kice). Our estimates of Kice were significantly lower than the Bridgman estimates, but in relatively good agreement with other more recent estimates.
Brekke S. E.
Catling David C.
Kargel Jeff S.
Marion Giles M.
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