  The Origins Space Telescope (OST) is one of four mission concepts currently
being studied by NASA in preparation for the Astrophysics 2020 Decadal Survey.
With active cooling (~4 K), OST will be sensitive in mid- to far-IR
wavelengths, using imaging and spectroscopy to probe the furthest reaches of
our galaxies, trace the path of water through star and planet formation, and
place thermochemical constraints on the atmospheres of exoplanets ranging in
size from Jupiter to Earth. This contribution to the Exoplanet Science Strategy
committee discusses the significant advancements that the OST Mid-Infrared
Imager, Spectrometer, and Coronagraph (MISC) instrument can make in studying
cool planetary atmospheres. We particularly focus on the atmospheres of
transiting rocky planets in the habitable zones of mid-to-late M stars. We
discuss how OST thermal infrared observations can significantly enhance our
understanding of the temperature structure and molecular abundances of
biologically interesting gases on these worlds, including O3, CH4, H2O, and
CO2.
