Will we know alien life when we see it?
Recognizing life on other worlds requires wiggle room in the definition of ‘life’
This is the third in a three-part series on the search for extraterrestrial life.
In a 1967 episode of Star Trek, Captain Kirk and his crew investigated the mysterious murders of miners on the planet Janus VI. The killer, it turned out, was a rock monster called the Horta. But the Enterprise’s sensors hadn’t registered any sign of life in the creature. The Horta was a silicon-based life-form. That made it different from any on Earth where everything is carbon-based.
Still, it didn’t take long to determine that the Horta was alive. The first clue was that it skittered about. Spock closed the case with a mind meld. He learned that the creature was the last of its kind, protecting a throng of eggs.
But recognizing life on different worlds isn’t likely to be this simple. It could prove especially hard if the recipe for life elsewhere does not include familiar ingredients. There may even be things alive on Earth that have been overlooked because they don’t fit standard definitions, some scientists suspect. The scientists that look for life outside Earth are called astrobiologists. They need some ground rules — with some built-in wiggle room — to know when they can confidently declare, “It’s alive!”
Among people working out those rules is Christoph Adami. He is a theoretical physicist at Michigan State University in East Lansing. He has watched his own version of silicon-based life grow. That life wasn’t real, though. It was a computer simulation.
“It’s easy when it’s easy,” Adami says. “If you find something walking around and waving at you, it won’t be that hard to figure out that you’ve found life.” But chances are, the first aliens that humans encounter won’t be little green men. They will probably be tiny microbes of one color or another — or perhaps no color at all.
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