In space, two is a magic number.
A single example of something out there—like a lone black hole, or only one solar system—could be a cosmic glitch, an astronomical anomaly.
But discover a second example, whatever it is—planets or pulsars—and lots more surely exist, say researchers. Millions, billions, trillions.
In astronomy, two extrapolates to infinity.
“Two is very, very different from one,” says Debra Fischer, the Yale professor and lead scientist for the school’s 100 Earths Project.
“The Rule of Two” also applies to the search for extraterrestrial life.
Far as we know, life resides only on Earth. But find it on another world—that second example—and scientists will conclude life is abundant in the galaxy. All over the place, if not everyplace.
And any kind of life will do. Even a primitive alien microbe. Even a fossilized microbe, dead for a billion years.
Just get to two.
Which is why the Mars samples are so intriguing; NASA’s rover Curiosity discovered organic molecules within the ancient rock.
The molecules aren’t alive, but they are carbon-based material, the precursors of life. “All of the things that life uses as building blocks,” Fischer says.
Perhaps the organics led to life—Martian microbes.
“If that happened with two rolls of the dice in our solar system,” says Fischer, “that’s stunning.”
Yet organic molecules alone, albeit significant, aren’t remarkable.
Says Fischer: “Prebiotic chemistry on other worlds is going to be common. Plenty of small rocky planets will have similar chemistry. It’s almost a given.”
What nobody knows: how often life latches on.
“That could happen one in a billion times—or one in every ten,” she says. "We have absolutely no idea."
What’s a virtual certainty: Microbes are the foundation for more complex life.
“You can’t go from prebiotic chemistry to assembling a dog, a dolphin, or a human being,” says Fischer.
“If few worlds have microbial life, it dramatically reduces the chances that more complex organisms exist.”
Just knowing that—how often microbes make it on planets with organics—may help scientists figure out how often the sophisticated life evolves.
And that's true whether they are things that crawl, slither, or swim—or, says Fischer—"build radio telescopes."
