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Project Progress

We have continued our fundamental experimental research into (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. Our work over the past year has continued to focus on the first and third issues. PhD students Philip Croteau and Emily Chu have upgraded our instrumentation and done experiments monitoring the kinetics of formation of hydrocarbon species more complex than CH₄ and of aerosols by light scattering. We can show 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 began a 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.