* Astronomy

Vegetation's Red Edge: A Possible Spectroscopic Biosignature of Extraterrestrial Plants
Earth's deciduous plants have a sharp order-of-magnitude increase in leaf reflectance between approximately 700 and 750 nm wavelength. This strong reflectance of Earth's vegetation suggests that surface biosignatures with sharp spectral features might be detectable in the spectrum of scattered light from a spatially unresolved extrasolar terrestrial planet.
A new study assess the potential of Earth's step-function-like spectroscopic feature, referred to as the "red edge", as a tool for astrobiology; and reviews the basic characteristics and physical origin of the red edge and summarize its use in astronomy: early spectroscopic efforts to search for vegetation on Mars and recent reports of detection of the red edge in the spectrum of Earthshine (i.e., the spatially integrated scattered light spectrum of Earth).
Earthshine observations from Apache Point Observatory emphasize that time variability is key to detecting weak surface biosignatures such as the vegetation red edge. The scientists briefly discuss the evolutionary advantages of vegetation's red edge reflectance, and speculate that while extraterrestrial "light harvesting organisms" have no compelling reason to display the exact same red edge feature as terrestrial vegetation, they might have similar spectroscopic features at different wavelengths than terrestrial vegetation. This implies that future terrestrial-planet-characterizing space missions should obtain data that allow time-varying, sharp spectral features at unknown wavelengths to be identified. They caution that some mineral reflectance edges are similar in slope and strength to vegetation's red edge (albeit at different wavelengths); if an extrasolar planet reflectance edge is detected care must be taken with its interpretation.

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