Simulating 3-D Biosignature Gases on Earths around other Stars

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The search for life beyond Earth is one of the big questions in the modern science community, and a primary motivation behind a range of NASA's ground-based and space-bourne missions. In the near future, the James Webb Space Telescope, LUVOIR, and HabEx will characterize the atmospheres of nearby Earth-like exoplanets. The main objective of these missions will be to measure absorption signatures of biogenic compounds (e.g., O3, CH4, N2O, CH3CL) in atmospheric transmission and reflection spectra. Detectability of these features however, depends on both the abundance and distribution of these biogenic gases in the upper atmosphere. Previous work has shown that biogenic gases vary according to the spectral intensity of a planet’s host star due to photochemical reaction rates. However, these findings are based on 1-D model simulations. Here I present preliminary develop three-dimensional characterizations of atmospheric biosignatures using a high-top climate-chemistry model (CCM) – CESM WACCM. In addition to modeling the altered photochemistry of a suite of stellar spectral types, the 3-D CCM will explicitly simulate atmospheric circulation, which could lead to  changes in the spatiotemporal distribution of biosignatures. For instance,line-of-sight-dependent signatures could result from different gas concentrations between the day and night-side of a planet. Such features may be found by comparing the transmission spectra between ingress and egress of transiting planets. Indeed, our initial analysis suggests that apart from photochemistry, circulation-induced anisotropy of biogenic molecules has critical influences on current observational strategies. Overall, my work will bolster our understanding of the atmospheric properties of rocky planets and inform upcoming missions in search of an Earth's analog.

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  • 04/05/2018
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