"Since NASA's Kepler telescope launched in 2009, the planet-hunting spacecraft has changed our conception of space over and over again. Our galaxy, it turns out, is rife with exoplanets, or planets orbiting other stars—some of them perhaps even habitable. Today, NASA announced Kepler has identified 500 more possible planets, bringing the total to 4,175. And one newly discovered exoplanet, Kepler 452b, may be the most Earth-like ever.
That's great and all, but still…kind of meaningless. We know of these planets now, but a more interesting question is: Could any of them really harbor life? And if they do, could any of them know of us?
Humankind, after all, has been inadvertently broadcasting electromagnetic waves since the invention of radio a century ago. Those early radio transmission were weak—too weak to even make it through Earth's ionosphere, says Seth Shostak, senior astronomer at the SETI Institute. With World War II came military radar and then television and FM radio. Those waves, which are all electromagnetic like light, would have since traveled about 70 light years away from Earth. The newly confirmed Kepler 452b, at 1,400 light years away, will not be seeing I Love Lucy for more than a millennium.
So how many planets are in this 70 light-year radius? Astronomers have found evidence of over 100. And how many are potentially habitable? Just thirteen.
But potentially habitable doesn't mean there's life—intelligent or otherwise—and actually, potentially habitable doesn't mean, uh, very much at all. "It's quite literally anyone's guess what those planets are like," says Greg Laughlin, an astronomer at the University of California, Santa Cruz.
Kepler finds exoplanets by detecting how a star dims as its planet transits across it…"
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