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Project Progress

With the 30% budget cuts to the NAI teams and redistribution of the remaining funds among the BioMARS team, funding for this project ended on 9/30/2007. Over this time period, we continued experiments on (1) whether or not a photochemical haze may have formed in Mars’ early atmosphere, (2) whether or not such a haze may have warmed or cooled the surface — that is, resulted in a greenhouse or “anti-greenhouse” effect, and (3) whether such an aerosol could have settled to the surface and provided a potentially “false biosignature” in the carbon-13 isotopic composition of organic matter in the martian rock record. PhD students Philip Croteau and Emily Chu continued experiments monitoring the kinetics of formation of hydrocarbon species more complex than CH₄ and of aerosols by light scattering showing that as a simulated atmosphere increases in CO₂ relative to CH₄, particle production at first increases as CO₂ increases and then markedly decreases, similar to results found by Trainer et al., PNAS, [2007] in a very different experimental set-up but contrary to earlier photochemical model predictions by Zahnle [1986] and Kasting et al. [1983]. The implications are that organic aerosols are likely to have been more prevalent on early Earth and Mars than photochemical models have predicted and could have had a significant influence on surface temperatures (and hence the stability of liquid water at the surface), depending on their optical properties. A manuscript is in preparation for publication of these results. We also continued our collaboration with Yuk Yung and co-workers at Caltech in comparing our laboratory results irradiating CH₄ with UV light with predictions from photochemical models in order to assess the strengths and weaknesses of photochemical model reaction schemes for planetary atmospheres run at room temperature [Wong et al., 2006], relevant for understanding atmospheric photochemistry, organic hazes, and the atmospheric production rates of prebiotic chemicals on Titan and, eventually, for more oxygen-rich atmospheres on early Earth and Mars. The comparison of lab and modeling results and sensitivity studies suggest that one or several key reactions may be orders of magnitude off and/or that a reaction scheme(s) other than those in the model predominate; the comparisons also point the way to model improvements as well as which key reactions need further scrutiny in the laboratory on an individual basis. A manuscript is now in final revisions for submission to Icarus. Finally, we began a more systematic investigation of the carbon-13 isotopic composition of aerosols produced in our experiments in a collaboration with David DesMarais and Michael Kubo of NASA Ames Research Center. Work is now continuing on several aspects of this project through partial support from the NASA Planetary Atmospheres Program, which will aid in seeing the project through to completion, including both publication of the final results and the awarding of PhDs to students Croteau and Chu.