STEVE INSKEEP, HOST:
Today, scientists grapple with a profound question - if we were ever to find alien life in the universe, how would we know? Whatever's out there might be really strange, unrecognizable. And the top people in astrobiology are talking about what to look for. Here's NPR's Nell Greenfieldboyce.
NELL GREENFIELDBOYCE, BYLINE: NASA is planning to send a probe to an icy moon of Jupiter called Europa. Beneath the ice lies a vast ocean of liquid water. So former astronaut John Grunsfeld recently asked some NASA colleagues, when we get to this water world, how exactly will we search for life?
JIM GREEN: We looked at him with blank faces.
GREENFIELDBOYCE: Jim Green is director of planetary science at NASA. Scientists like him know how to recognize life on Earth because everything here shares a common ancestry. But he says life began way out there might look very different.
GREEN: What do we need to build to really find life? What are the instruments? What are the techniques? What are the things that we should be looking for?
GREENFIELDBOYCE: These are the questions NASA officials have asked the prestigious National Academy of Sciences to help them answer, with a meeting that starts today in California. The academy's rounded up the small crew of people who contemplate the chemistry of hypothetical aliens, including Steven Benner from the Foundation for Applied Molecular Evolution.
STEVEN BENNER: It's a bit of a crackpot field, right? If you're interested as a young scientist is setting up a career, it makes much more sense to do cancer research.
GREENFIELDBOYCE: All joking aside, the stakes here are huge. NASA doesn't want a repeat of what happened in the 1970s with the Viking landers on Mars. Their analysis of the Martian soil showed ambiguous signs of life that never panned out. Jim Kasting is with Penn State University.
JIM KASTING: I remember the aftermath of that. NASA was criticized heavily for looking for life before they had investigated the planet and for not having thought that through carefully.
GREENFIELDBOYCE: Four decades later, he says, there's still no scientific consensus on the best way to find alien life.
KASTING: We have big debates about it, actually, and that's part of what this meeting is all about.
GREENFIELDBOYCE: And these days, the search for life faces a new challenge. Scientists have detected planets beyond our solar system around distant stars. They're so far away you can't send a probe to scoop up soil or slurp up liquid. All you can do is use telescopes to get hints about a planet's atmosphere. Scientists argue over what combination of gases might suggest life is there. William Bains of MIT says, hey, a plant-like lifeform might produce hydrogen instead of oxygen. Over Skype, he told me he's pessimistic about finding aliens in his lifetime. Still, he says...
WILLIAM BAINS: Even getting a hint that there's life elsewhere would just be really sort of philosophically and socially a fascinating thing to find out. I think it's a really important quest.
GREENFIELDBOYCE: That's why he'll be there at the meeting with the usual suspects. Nell Greenfieldboyce, NPR News.
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