title: Biosignatures from Earth-like planets around M dwarfs.
abstract: Coupled one-dimensional photochemical-climate calculations have been performed for hypothetical Earth-like planets around M dwarfs. Visible/near-infrared and thermal-infrared synthetic spectra of these planets were generated to determine which biosignature gases might be observed by a future, space-based telescope. Our star sample included two observed active M dwarfs-AD Leo and GJ 643-and three quiescent model stars. The spectral distribution of these stars in the ultraviolet generates a different photochemistry on these planets. As a result, the biogenic gases CH4, N2O, and CH3Cl have substantially longer lifetimes and higher mixing ratios than on Earth, making them potentially observable by space-based telescopes. On the active M-star planets, an ozone layer similar to Earth's was developed that resulted in a spectroscopic signature comparable to the terrestrial one. The simultaneous detection of O2 (or O3) and a reduced gas in a planet's atmosphere has been suggested as strong evidence for life. Planets circling M stars may be good locations to search for such evidence.
authors.affiliation: Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125, USA. antígona@ipac.caltech.edu
authors.forename: Antígona
authors.initials: A
authors.lastname: Segura
authors.forename: James F
authors.initials: JF
authors.lastname: Kasting
authors.forename: Victoria
authors.initials: V
authors.lastname: Meadows
authors.forename: Martin
authors.initials: M
authors.lastname: Cohen
authors.forename: John
authors.initials: J
authors.lastname: Scalo
authors.forename: David
authors.initials: D
authors.lastname: Crisp
authors.forename: Rebecca A H
authors.initials: RA
authors.lastname: Butler
authors.forename: Giovanna
authors.initials: G
authors.lastname: Tinetti
mesh_terms: D055580:Astronomical Phenomena; D001256:Astronomy; D001272:Atmosphere; D005118:Extraterrestrial Environment / Q000737:chemistry*; D019369:Life; D008697:Methane / Q000032:analysis; D008737:Methyl Chloride / Q000032:analysis; D009609:Nitrous Oxide / Q000032:analysis; D010100:Oxygen / Q000032:analysis; D010126:Ozone / Q000032:analysis; D010777:Photochemistry; D016083:Planets; D013057:Spectrum Analysis; D014466:Ultraviolet Rays
chemical_list: D010126:Ozone; D008737:Methyl Chloride; D009609:Nitrous Oxide; D008697:Methane; D010100:Oxygen