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Project Progress

This task focuses on the development of a generalized, comprehensive, photochemical model for terrestrial planet atmospheres, by evolving a version of the Caltech/JPL planetary chemistry/transport model, KINETICS. The resulting model interacts with the climate model described in Task 2, to create a self-consistent climate-chemical model.

This year, we finished compiling the master reaction list from individual reaction lists for Venus, Earth, Mars, Jupiter, Saturn, and Titan. This comprehensive set can now be used for a wide range of planetary environments, and template sets for Venus-like, Earth-like, and Mars-like planets were also developed as starting points for simulations.

The interface to link the chemical model and other components of the VPL suite through the VPL database was developed. To improve data input and versatility, different input formats for photochemical parameters are now supported. The same stellar radiation input to the radiative and climate components of the model, albeit degraded to lower resolution, is now used. Finally, the chemical model can now ingest and use climatological data from the VPL database, and transfer computed atmospheric composition data back to the database for use by the climate model, in a fully iterative fashion.

In parallel with the interface to VPL, KINETICS was used to investigate the chemistry of the atmosphere of Titan, and model chemical changes in a Snowball Earth. The latter study showed that a weak Snowball hydrological cycle coupled with photochemical reactions with water vapor would result in steady state production and accumulation of hydrogen peroxide, H₂O₂, which would be released directly into the ocean in the melting at Snowball’s end. This phenomenon could explain massive deposition of Mn oxides in post-glacial sediments and could have driven the evolution of oxygen mediating enzymes and oxygenic photosynthesis.

The atmospheric fractionation of CH₄ on Mars was also investigated. Biological processes can fractionate the common isotopologues of methane, although additional fractionation due to photochemistry also occurs. This work on understanding the atmospheric fractionation processes therefore supports the interpretation of isotopic ratios to identify the source of the Mars methane.