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Project Progress

Work related to this task moved forward on several fronts, from the deep interior of planets to the top of planetary atmospheres. Nimmo took the lead in the interior, adding melt generation to his existing parameterized thermal evolution code. This model simulates the transport of heat and materials between the interior and surface of planets with or without plate tectonics. The model now allows melting to occur at both mid-ocean ridges and upwellings. Melt extraction removes incompatible elements from the mantle; these elements return to the mantle if there are subduction zones, or are lost to the system if they are volatile. The removal of incompatible radiogenic elements from the mantle results in a reduction in the amount of internal heating.

We are incorporating the dominant rock-forming minerals into our models that simulate kinetically controlled weathering. Our general models will help constrain the evolution of mineralogies of other habitable planetary surfaces and their volatile fluxes. We have used such a model to show that with >1 ppm atmospheric oxygen, (Rye et al. 1995), constraints on pre-2.2-billion-year-ago carbon dioxide levels using paleosol chemistry and mineralogy remain applicable. Incorporation of microbially enhanced kinetic rates of reactions will allow future models to assess changes on volatile exchange expected due to life.

Kasting and Parkinson worked on a new model of hydrodynamic loss processes from planetary atmospheres. Their method seeks to overcome the instabilities inherent in modeling transonic conditions by solving the coupled, time-dependent mass, momentum, and energy equations, instead of integrating time-independent equations. Several model modules are largely working, including the core solver, atmospheric setup, gravitation, heating, thermal conductivity, viscosity, tidal forces, and geometrical considerations. Work continues on the problem of damping in the top layers of the model amosphere.