Synthetic Spectra of Simulated Terrestrial Atmospheres Containing Possible Biomarker Gases

NASA's proposed Terrestrial Planet Finder, a space-based interferometer, will eventually allow spectroscopic analyses of the atmospheres of extrasolar planets. Such analyses would provide information about the existence of life on these planets. One strategy in the search for life is to look fo...

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Bibliographic Details
Published in:Icarus (New York, N.Y. 1962) N.Y. 1962), 2000-05, Vol.145 (1), p.262-271
Main Authors: Schindler, Trent L., Kasting, James F.
Format: Article
Language:English
Subjects:
Astronomy - methods
Atmosphere - analysis
Atmosphere - chemistry
Biomarkers
Exobiology
Extraterrestrial Environment
Methane - analysis
Models, Chemical
Ozone - analysis
Planets
Space life sciences
Spectrum Analysis
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Summary:NASA's proposed Terrestrial Planet Finder, a space-based interferometer, will eventually allow spectroscopic analyses of the atmospheres of extrasolar planets. Such analyses would provide information about the existence of life on these planets. One strategy in the search for life is to look for evidence of O 3 (and hence O 2) in a planet's atmosphere; another is to look for gases that might be present in an atmosphere analogous to that of the inhabited early Earth. In order to investigate these possibilities, we have calculated synthetic spectra for several hypothetical terrestrial-type atmospheres. The model atmospheres represent four different scenarios. The first two, representing inhabited terrestrial planets, are an Earth-like atmosphere containing variable amounts of oxygen and an early Earth-type atmosphere containing methane. In addition, two cases representing Mars-like and early Venus-like atmospheres were evaluated, to provide possible “false positive” spectra. The calculated spectra suggest that ozone could be detected by an instrument like Terrestrial Planet Finder if the O 2 concentration in the planet's atmosphere is ≥200 ppm, or 10 −3 times the present atmospheric level. Methane should be observable on an early-Earth type planet if it is present in concentrations of 100 ppm or more. Methane has both biogenic and abiogenic sources, but concentrations exceeding 1000 ppm, or 0.1% by volume, would be difficult to produce from abiogenic sources alone. High methane concentrations in a planet's atmosphere are therefore another potential indicator for extraterrestrial life.
ISSN:0019-1035
1090-2643
DOI:10.1006/icar.2000.6340