@article{TEXTUAL,
      recid = {13711},
      author = {Schwieterman, Edward W. and Reinhard, Christopher T. and  Olson, Stephanie L. and Ozaki, Kazumi and Harman, Chester  E. and Hong, Peng K. and Lyons, Timothy W.},
      title = {Rethinking CO Antibiosignatures in the Search for Life  Beyond the Solar System},
      journal = {The Astrophysical Journal},
      address = {2019-03-15},
      number = {TEXTUAL},
      abstract = {Some atmospheric gases have been proposed as counter  indicators to the presence of life on an exoplanet if  remotely detectable at sufficient abundance (i.e.,  antibiosignatures), informing the search for biosignatures  and potentially fingerprinting uninhabited habitats.  However, the quantitative extent to which putative  antibiosignatures could exist in the atmospheres of  inhabited planets is not well understood. The most commonly  referenced potential antibiosignature is CO, because it  represents a source of free energy and reduced carbon that  is readily exploited by life on Earth and is thus often  assumed to accumulate only in the absence of life. Yet,  biospheres actively produce CO through biomass burning,  photooxidation processes, and release of gases that are  photochemically converted into CO in the atmosphere. We  demonstrate with a 1D ecosphere-atmosphere model that  reducing biospheres can maintain CO levels of ∼100 ppmv  even at low H<sub>2</sub> fluxes due to the impact of  hybrid photosynthetic ecosystems. Additionally, we show  that photochemistry around M dwarf stars is particularly  favorable for the buildup of CO, with plausible  concentrations for inhabited, oxygen-rich planets extending  from hundreds of ppm to several percent. Since  CH<sub>4</sub> buildup is also favored on these worlds, and  because O<sub>2</sub> and O<sub>3</sub> are likely not  detectable with the James Webb Space Telescope, the  presence of high CO (>100 ppmv) may discriminate between  oxygen-rich and reducing biospheres with near-future  transmission observations. These results suggest that  spectroscopic detection of CO can be compatible with the  presence of life and that a comprehensive contextual  assessment is required to validate the significance of  potential antibiosignatures.},
      url = {http://knowledge.uchicago.edu/record/13711},
}