Biology
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006apj...644..551t&link_type=abstract
The Astrophysical Journal, Volume 644, Issue 1, pp. 551-559.
Biology
28
Astrobiology, Earth, Moon, Stars: Planetary Systems
Scientific paper
To characterize the spectrum of Earth viewed as an extrasolar planet, we observed the spatially integrated near-infrared (0.7-2.4 μm) reflection spectrum of Earth via the dark side of the Moon (earthshine). After contributions from the Sun, Moon, and local atmosphere were removed, the resulting spectrum was fitted with a simple model of the reflectivity of Earth. The best model fit is dominated by the reflection spectrum of the atmosphere above medium-altitude water clouds, with lesser contributions from high-altitude ice clouds and from the ground. The spectral features seen are H2O (six strong band structures from 0.7 to 2.0 μm), CO2 (six moderate-strength features from 1.4 to 2.1 μm), O2 (two moderate-strength features at 0.76 and 1.26 μm), and several weak CH4 features. Interpreted as a spectrum of an extrasolar planet, we would confidently conclude that this is a habitable planet, based on the presence of strong water bands. Furthermore, the simultaneous presence of oxygen and methane is a strong indicator of biological activity. We might also conclude that the planet is geologically active, based on the presence of CO2, water, and a dynamic atmosphere (inferred from cirrus clouds, cumulus clouds, and clear-air fractions in our model fit). This suggests that it would be valuable for the Terrestrial Planet Finder-Coronagraph (TPF-C) mission to include near-infrared spectroscopy capability. On the basis of the present work, we suggest that future long-term monitoring of the earthshine would allow us to discern how the globally integrated spectrum changes with planet rotation, cloud cover, and seasons.
Gorlova Nadya
Jucks Kenneth W.
Meyer Michael R.
Skrutskie Michael F.
Traub Wesley A.
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