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Post Info TOPIC: Vegetation's Red Edge:


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Exoplanet Vegetation
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Black plants 'could grow' on exoplanets with two suns

Plants on distant hospitable planets could have developed black foliage and flowers to survive, according to a new study.
Flora that would appear black or grey to human eyes could have evolved on planets orbiting dim "red dwarf" stars, according to unpublished research that is being presented at the National Astronomy Meeting in Llandudno, Wales.

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Alien Vegetation
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Could black trees blossom in a world with two suns?

A sky with two suns is a favourite image for science fiction films, but how would a binary star system affect life evolving on an orbiting planet?
O'Malley-James of the University of St Andrews has studied what plants might be like on an Earth-like planet with two or three suns and found that they may appear black or grey.  He will be presenting results at the RAS National Astronomy Meeting in Llandudno on Tuesday 19th April.

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Vegetation Red Edge
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Could an alien astronomer have detected life on Earth during an ice age? Recent work has calculated how past climate extremes affected the light reflected from vegetation out into space. The results could give hope to our own search for life on distant worlds.
From far away, our planet is a single faint speck of light in the sky. Although we have sent radio messages out to potential extraterrestrial listeners, none of these signals have travelled more than a few tens of light years.
However, Earthlings have been broadcasting their presence to the galaxy for millions of years. Terrestrial plants reflect strongly in the infrared, resulting in a distinctive feature (called the vegetation red edge or VRE) in the light bouncing off the Earth's surface.

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Vegetation Red-Edge
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Title: The Earth as an extrasolar planet: The vegetation spectral signature today and during the last Quaternary climatic extrema
Authors: Luc Arnold (OHP), François-Marie Bréon (CEA-DSM-LSCE), Simon Brewer (CEREGE)

The so-called Vegetation Red-Edge (VRE), a sharp increase in the reflectance around 700 nm, is a characteristic of vegetation spectra, and can therefore be used as a biomarker if it can be detected in an unresolved extrasolar Earth-like planet integrated reflectance spectrum. Here we investigate the potential for detection of vegetation spectra during the last Quaternary climatic extrema, the Last Glacial Maximum (LGM) and the Holocene optimum, for which past climatic simulations have been made. By testing the VRE detectability during these extrema when Earth's climate and biomes maps were different from today, we are able to test the vegetation detectability on a terrestrial planet different from our modern Earth. Data from the Biome3.5 model have been associated to visible GOME spectra for each biome and cloud cover to derive Earth's integrated spectra for given Earth phases and observer positions. The VRE is then measured. Results show that the vegetation remains detectable during the last climatic extrema. Compared to current Earth, the Holocene optimum with a greener Sahara slightly increases the mean VRE on one hand, while on the other hand, the large ice cap over the northern Hemisphere during the LGM decreases vegetation detectability. We finally discuss the detectability of the VRE in the context of recently proposed space missions.

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Vegetation's Red Edge:
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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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