How alien Earths will reveal their secrets

The European Space Agency has set itself an ambitious goal: to recognise the biomarkers on Earth-like planets orbiting other stars.

The first step in such an endeavour is work out to look for, which the goal that Lisa Kaltenegger at the Harvard-Smithsonian Center for Astrophysics in Cambridge  and Franck Selsis at the Laboratoire d’Astrophysique de Bordeaux in France have set themselves.

“The spectrum of the planet can contain signatures of atmospheric species that are important for habitability, like CO2 and H2O, or resulting from biological activity (O3, CH4, and N2O),” they say.  “The presence or absence of these spectral features will indicate similarities or differences with the atmospheres of terrestrial planets.”

But  just how similar is a question of some controversy. In one of the most fascinating papers of all time, Carl Sagan and friends analyzed a spectrum of the Earth taken by the Galileo probe, searching for signatures of life. They concluded that the large amount of O2 and the simultaneous presence of CH4 traces are strongly suggestive of biology.

But a more detailed study of this parameter space is necessary and not just from a theoretical point of view, conclude Kaltenegger and Selsis.

And time is short. With over 300 giant exoplanets already detected it is only a matter of time, maybe only months, before astrobiologists will have their first alien test case to analyse.

Ref: Atmospheric Modeling: Setting Biomarkers in Context

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