I’M WITNESSING the future of the search for alien life. In a dimly lit office on the 17th floor of MIT’s tallest building, with shades drawn over the Charles river below, Sara Seager and six other researchers are showing me the foundation stones of a vast library of molecules – a few of which may be the first to alert us to the presence of life on another world.

Seager and her colleagues are building a cache of biosignatures – chemicals that would suggest an alien planet is playing host to life. Seager is casting her net as wide as possible. Because we can’t predict what the biochemistry and ecology of alien planets will be like, she’s looking at all small molecules, not just the ones linked to life as we know it.

“Is there any limit to what sort of gas life can produce?” asks biochemist William Bains at the University of Cambridge. “Conceptually, the answer is no.”

Finding such signals is no pipe dream. Two upcoming NASA missions – the Transiting Exoplanet Survey Satellite (TESS), slated for launch in 2017, and the…

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photo caption: Life’s a gas on other earths (Image: Detlev Van Ravenswaay/SPL)