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Project Progress

Internal Processes and Habitability : A preliminary version of the generic terrestrial planet thermal evolution code has been completed and integrated with the VPL. This model calculates melt generation and volatile fluxes as a function of time for either stagnant-lid or plate tectonic cases. Species currently tracked include H₂O, CO₂ , SO₂ and radiogenic noble gases.

Team members also explored serpentinization, the most massive aphotosynthetic energy source, as potential food for microbes, reviewed the history of Earth’s oxygen, and concluded that methane-aided hydrogen escape did indeed supply oxygen to superficial reservoirs, and used the presence of chert clasts and sands to constrain the Earth’s surface temperature at ~3.2Ga to less than 50C.

Weathering: We continued work on the weathering of rocks and soils. Our black shale weathering model indicated that most ancient organic matter would be oxidized before reaching the surface, except for very rapid erosion rates. We have assembled mineralogic compositions for typical igneous rock types in preparation for modeling weathering of abiotic terrestrial planets, with special focus on fluxes of volatile gases that could, over time, change planetary atmospheric compositions. We also explored the implications of hypothesized high-temperature Archean conditions on granite weathering, and found that the mineral modes at the surface were dramatically affected. Modeling of contact metamorphism was initiated with the ultimate goal of addressing long-term surface CO₂ fluxes.

Exospheric Processes: We continued our study of the delivery of organics to habitable planets, including work on the ablation of organics from micrometeoroids, in collaboraiton with Don Brownlee (U. Wash) and George Cody (CIW), and new work on the chemical kinetics of polycyclic aromatic hydrocarbons (PAHs) in impacts and in circumstellar disks. PAHs would have been a potentially important source of carbon on the early earth and on other habitable planets, both as an abundant source of prebiotic carbon and a component of haze formation, which could have provided a UV shield in anoxic atmospheres. Work was also performed on the difficulty of forming hydrocarbon aerosols without methane in extrasolar giant planet atmospheres, and large impacts on Solar System bodies.