Simulating 3-D Biosignatures from Proxima Centauri with a Global Chemistry-Climate Model howard chen
Proxima Centauri b is one of the most promising extrasolar terrestrial planets to search for potential biomarkers, trace gases indicating signs of life beyond Earth. Due to its high planet to stellar luminosity ratio and high transit probability, Proxima b is a prime target for follow-up characterization efforts by e.g., NASA's James Webb Space Telescope, directing imaging missions, and even in situ analysis by the Breakthrough Starshot initiative. High-resolution, 3-D model predictions of atmospheric biosignatures however, are not currently available in the community. Here we use the CESM1 WACCM, a high-top coupled climate-chemistry general circulation model, to simulate the circulation, photochemistry, and stratospheric chemistry of Proxima b. From our equilibrium simulations, we find increased mixing ratios and lifetimes for biogenic compounds (e.g., CH4, N2O, and CH3Cl) in the stratosphere. Whereas these biogenic compounds are typically concentrated at the equator on Earth, they are dispersed across the mid-latitudes and even to the poles of Proxima b. Our initial analysis suggests that these characteristics are the result of a markedly energized stratospheric circulation regime and altered photochemistry, both of which are the consequence of enhanced UV and IR radiative forcing relative to Earth. Model simulated global distribution and longer lifetimes of biomarkers suggest that Proxima b’s molecular absorption and observational windows are potentially greater than anticipated. These results indicate enhanced prospects for detecting signals of biological activity on Proxima b and/or other M-dwarf planets via ground-based and space-borne missions by NASA.