From Nature:

T. Pyle/JPL-Caltech/NASA Ames

Astronomers have found dozens of exoplanets that might contain liquid water, and perhaps support life.

In the search for life beyond Earth, false alarms abound. Researchers have generally considered, and rejected, claims ranging from a 1970s report of life on Mars to the 1990s ‘discovery’ of fossilized space microbes in a meteorite.

Now, inspired by the detection of thousands of planets beyond the Solar System, NASA has started a fresh effort to learn how to recognize extraterrestrial life. The goal is to understand what gases alien life might produce — and how Earth-bound astronomers might detect such ‘biosignatures’ in light passing through the atmospheres of planets trillions of kilometres away (see ‘Searching for alien life’).

Source: Chart: S. Seager & W. Bains Sci. Adv. 1, e1500047 (2015); Cone: Ref. 5

The agency will convene a workshop this week in Seattle, Washington, with the ultimate goal of advising a NASA exoplanet group on how to avoid embarrassing errors in the future. “We have to come together and determine what good evidence of life on another planet could be,” says Shawn Domagal-Goldman, one of the workshop’s organizers and an astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

The exercise comes at a crucial time, as astronomers grapple with how to interpret exoplanet data from the next generation of telescopes. Some scientists are working to understand how nature could produce archetypal biosignature gases, such as oxygen, in the absence of living organisms. Others are trying to think as expansively as possible about the types of biochemistry that could sustain life.

“We could fool ourselves into thinking a lifeless planet has life — or we could be missing life because we don’t really understand the context of what could be produced on another planet,” says Sarah Rugheimer, …

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