Sara Seager2014-03-17 4:56 PM

对外太阳系类地行星的行星性质和生物信号的遥感 Remote Sensing of Planetary Properties and Biosignatures on Extrasolar Terrestrial Planets 

Abstract

The major goals of NASA’s Terrestrial Planet Finder (TPF) and the European Space Agency’s Darwin missions are to detect terrestrial-sized extrasolar planets directly and to seek spec- troscopic evidence of habitable conditions and life. Here we recommend wavelength ranges and spectral features for these missions. We assess known spectroscopic molecular band fea- tures of Earth, Venus, and Mars in the context of putative extrasolar analogs. The preferred wavelength ranges are 7–25 mm in the mid-IR and 0.5 to ,1.1 mm in the visible to near-IR. Detection of O2 or its photolytic product O3 merits highest priority. Liquid H2O is not a bioindicator, but it is considered essential to life. Substantial CO2 indicates an atmosphere and oxidation state typical of a terrestrial planet. Abundant CH4 might require a biological source, yet abundant CH4 also can arise from a crust and upper mantle more reduced than that of Earth. The range of characteristics of extrasolar rocky planets might far exceed that of the Solar System. Planetary size and mass are very important indicators of habitability and can be estimated in the mid-IR and potentially also in the visible to near-IR. Additional spec- troscopic features merit study, for example, features created by other biosignature compounds in the atmosphere or on the surface and features due to Rayleigh scattering. In summary, we find that both the mid-IR and the visible to near-IR wavelength ranges offer valuable infor- mation regarding biosignatures and planetary properties; therefore both merit serious scien- tific consideration for TPF and Darwin. Key Words: Spectroscopy—Biosignatures—Extraso- lar planets—Terrestrial Planet Finder—Darwin—Habitable planets. Astrobiology 2, 153–181.

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Sara Seager

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