2012 Annual Science Report

Arizona State University Reporting  |  SEP 2011 – AUG 2012

Habitability of Water-Rich Environments, Task 1: Improve and Test Codes to Model Water-Rock Interactions

Project Summary

The new computer codes could be used to calculate changes in phase composition during freezing or melting in cold icy environments on Mars, large water-bearing asteroids, icy moons of giant planets, comets, and other trans-neptunian objects. Another model will allow us to calculate composition of liquid hydrocarbons on the surface of Titan.

4 Institutions
3 Teams
1 Publication
0 Field Sites
Field Sites

Project Progress

Recent SESE graduate Chris Glein (now at the Carnegie Institution of Washington) completed development of a thermodynamic model that can be used to predict phase equilibria between solids, liquids, and gases in the CH4-C2H6-C3H8-N2-C2H2 system at temperatures near the triple point of CH4. The model can be used to explore geochemical processes on Saturn’s moon Titan. The model uses standard states based on Raoult’s law, and accounts for non-ideal behavior in mixtures using an empirical modification of the regular solution theory of van Laar. Experimental phase equilibrium data were used to parameterize and test the model. It was determined that the model generally gives more accurate results than comparable, existing models. We expect the model to become a useful tool to the Titan research community because the model has a good balance between accuracy and simplicity, and can be expanded to any number of components while maintaining strict thermodynamic consistency.

The FREZCHEM code was significantly modified by Co-I Mikhail Mironenko in collaboration with Dr. Giles Marion. The code is to calculate chemical equilibria in aqueous electrolyte solutions with low water activities, such as salt solutions. The thermodynamic database of the FREZCHEM code was updated with equilibrium constants of chemical reactions and Pitzer parameters for CO2 and CH4 gas hydrates, aluminum-bearing species, ammonia, and ammonium, ferric iron, and perchlorate ions. The equilibrium constants of individual reactions were recalculated to be used for equilibrium computations with the free energy minimization method. A new version of FREZCHEM code will be publically available at the website of Desert Research Institute (www.dri.edu). The new code could be used to calculate phase composition and water activity during melting or freezing of salt-, ammonia-, CO2-, and methane-bearing systems on multiple bodies in the outer solar system.

Co-I Mikhail Mironenko has developed a new model for calculating chemical equilibria in CO2-bearing water electrolyte systems. The work is done in collaboration with Dr. V. Polyakov. The model includes liquid carbon dioxide and solid hydrate (CO2*6H2O, CO2 clathrate), and incorporates the equation of state for CO2 (Span and Wagner, 1996) into the FREZCHEM database. The code was tested through calculations of phase composition in heated/cooled isochoric systems via iterative runs of isobaric equilibria. The code could be applied to cold icy and salty aqueous systems with abundant CO2 on icy moons and Mars.

Co-Is M. Mironenko and M. Zolotov published the algorithm of the coupled thermodynamic-kinetic model for aqueous alteration of rocks. The model is illustrated by calculation of granite sand alteration.