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标题：Surface biosignatures of exo-Earths: Remote detection of extraterrestrial life
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作者：Siddharth Hegde ; Ivan G. Paulino-Lima ; Ryan Kent 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：13
页码：3886-3891
DOI：10.1073/pnas.1421237112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceWe develop the first catalogue, to our knowledge, of reflectance spectra for a diverse range of pigmented microorganisms, including ones that were isolated from Earth's most extreme environments. This catalogue provides a broad scope of surface signatures for life on exoplanets, which could provide different conditions from those on Earth, allowing, for example, extremophiles on Earth to become the predominant life form. Much of the history of life on Earth has been dominated by microbial life, and it is likely that life on exoplanets evolves through single-celled stages prior to multicellular creatures. Here, we present the first database, to our knowledge, for such surface features in preparation for the next generation of space- and ground-based telescopes that will search for a wide variety of life on exoplanets. 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 {micro}m) 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 {micro}m) 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.
关键词：biosignatures ; spectral library ; reflectivity ; extremophiles ; pigments