title: Surface biosignatures of exo-earths: remote detection of extraterrestrial life.
abstract: Exoplanet discovery has made remarkable progress, with the first rocky planets having been detected in the central star's liquid water habitable zone. The remote sensing techniques used to characterize such planets for potential habitability and life rely solely on our understanding of life on Earth. The vegetation red edge from terrestrial land plants is often used as a direct signature of life, but it occupies only a small niche in the environmental parameter space that binds life on present-day Earth and has been widespread for only about 460 My. To more fully exploit the diversity of the one example of life known, we measured the spectral characteristics of 137 microorganisms containing a range of pigments, including ones isolated from Earth's most extreme environments. Our database covers the visible and near-infrared to the short-wavelength infrared (0.35-2.5 µm) portions of the electromagnetic spectrum and is made freely available from biosignatures.astro.cornell.edu. Our results show how the reflectance properties are dominated by the absorption of light by pigments in the visible portion and by strong absorptions by the cellular water of hydration in the infrared (up to 2.5 µm) portion of the spectrum. Our spectral library provides a broader and more realistic guide based on Earth life for the search for surface features of extraterrestrial life. The library, when used as inputs for modeling disk-integrated spectra of exoplanets, in preparation for the next generation of space- and ground-based instruments, will increase the chances of detecting life.
authors.affiliation: Max Planck Institute for Astronomy, Heidelberg 69117, Germany; shegde@astro.cornell.edu.
authors.forename: Siddharth
authors.initials: S
authors.lastname: Hegde
authors.affiliation: National Aeronautics and Space Administration Postdoctoral Program Fellow, National Aeronautics and Space Administration Ames Research Center, Moffett Field, CA 94035;
authors.forename: Ivan G
authors.initials: IG
authors.lastname: Paulino-Lima
authors.affiliation: University of California, Santa Cruz University Affiliated Research Center, National Aeronautics and Space Administration Ames Research Center, Moffett Field, CA 94035;
authors.forename: Ryan
authors.initials: R
authors.lastname: Kent
authors.affiliation: Max Planck Institute for Astronomy, Heidelberg 69117, Germany; Institute for Pale Blue Dots, Department of Astronomy, Cornell University, Ithaca, NY 14853; and.
authors.forename: Lisa
authors.initials: L
authors.lastname: Kaltenegger
authors.affiliation: National Aeronautics and Space Administration Ames Research Center, Moffett Field, CA 94035.
authors.forename: Lynn
authors.initials: L
authors.lastname: Rothschild
mesh_terms: D017033:Anabaena / Q000502:physiology; D044822:Biodiversity; D002708:Chlorella / Q000502:physiology; D018534:Earth, Planet; D018559:Exobiology / Q000379:methods*; D005118:Extraterrestrial Environment; D055352:Halorubrum / Q000502:physiology; D019369:Life; D008027:Light; D008855:Microscopy, Electron, Scanning; D016083:Planets; D013053:Spectrophotometry
keywords: biosignatures; extremophiles; pigments; reflectivity; spectral library