FROM THEORY TO OBSERVATION: THE DATA DRIVEN TRANSITION FROM THERMODYNAMICS TO KINETICS IN MARS GEOCHEMISTRY

Geochemical models of Mars have transitioned over the past two decades from thermodynamic predictions of mineral assemblages based on P-T-X conditions, to thermodynamic- kinetic models of geochemical processes based on observations of outcrops in situ and detailed analysis of meteorites. Extensive datasets from Mars landers and orbiters have resulted in fresh models of the geologic history of the planet and the processes active at its surface. In many cases, both kinetics and thermodynamics are needed to interpret observed mineral assemblages, resulting in nuanced analysis of geologic processes as well as the P-T-X conditions under which mineral assemblages may have formed. The integration of kinetics in planetary geochemistry has broadened the field of research. Geochemical models of chemical weathering and aqueous alteration and experimental studies have investigated mineral dissolution and precipitation kinetics in Mars analogue environments. In addition, the kinetics of phase transitions within new systems, including gas hydrates have been determined. These studies yield constraints on the duration of aqueous processes on the surface of Mars and lead to new questions. Future and continuing missions, as well as laboratory studies, which integrate both thermodynamics and kinetics will continue to reveal a more detailed picture of the processes that have resulted in the surface materials we observe today.