Exoplanet Atmospheres and SETI
Narrowing the Search: SETILive is a part of the much larger, much broader and rapidly advancing field of exoplanetary research. The “S” in SETI stands for “search” and these advances will directly benefit SETI by narrowing the search. The current explosion in exoplanet discoveries ignited by the Kepler project is providing great fundamental data for planetary and astrobiology scientists to begin figuring out exactly how planets form and develop and what the prospects for life on these planets could be. The more they learn, the narrower the search for ET can be.
The SETI Institute’s concentration on these Kepler planets, with SETILive as a part of it, is an early example of this more informed search, focusing for the first time on a large number of planets that have good evidence that they could be in the water-based habitable zone. The new wave of discoveries that will help narrow down this search even more is the analysis of exoplanet atmospheres – finding out what gases are present. Some of these gases, if found, could be a strong indication that a planet hosts life at some level, and quite possibly intelligent life.
New Techniques: A sign of the progress being made in the study of exoplanet atmospheres is this work done through the European Southern Observatory also reported on spacedaily.com. Here, they are directly measuring the very weak “rainbow” of colors from the planet’s faint infrared glow produced by its own heat. This new technique is different than the method of seeing how the planet’s atmosphere affects the rainbow spectrum of the starlight behind it during a transit. It is based on that fact that, like a star, a planet’s own rainbow spectrum is affected by gases that surround it. The difference is that the planet’s rainbow light is very much weaker than a star’s and it’s concentrated in infrared wavelengths that are far out of the range visible to our eyes.
On the Horizon: So far, exoplanet atmospheric measurements are only feasible for large planets like this Jupiter-class one in a nearby star system. Measurements for smaller (earth-class), and more distant planets will come along in the coming decades as new instruments like the James Webb Space Telescope and the new giant ground-based telescopes come into play.
I feel that we’re at the beginning of a very exciting few decades in the search for extraterrestrial life in general and SETI in particular.
SETILive 
Maybe in the not too far future (say ten to fifteen years), large optical interferometers, equipped with imaging spectrometers could be placed into orbit (perhaps at the Earth-Sun L2 point). We could look for the spectral signature of ozone in the atmospheres of super-earth or earth-like planets. Ozone would be an excellent “biosignature” in that it would indicate the presence of molecular oxygen. Since oxygen can only be produced by living organisms, this would provide “smoking gun” evidence of at least primitive life on the planet under study.
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