If You're Looking For Alien Life, How Will You Know If You've Found It?

"When a robotic probe finally lands on a watery world like Jupiter's moon Europa, what do scientists have to see to definitively say whether the place has any life?"

"That's the question retired astronaut John Grunsfeld posed to some colleagues at NASA when he was in charge of the agency's science missions."

"'We looked at him with blank faces,' recalls Jim Green, head of NASA's planetary sciences division. '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?'"

"To get some advice, the agency recently asked the prestigious National Academies of Sciences, Engineering, and Medicine to gather some of the top experts in astrobiology for a meeting that begins Monday."