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An illustration imagines what Kepler-186f may look like.

An illustration imagines what Kepler-186f may look like.

T. Pyle/NASA Ames/SETI Institute/JPL-Caltech

Let's face it, the evidence is hard on the case for life elsewhere in the universe. This, of course, doesn't mean that there is no life on another world. We couldn't ever make a statement like that. Science is better at finding things than at ruling things out. Or, as Carl Sagan used to say, "the absence of evidence is not evidence of absence."

"They" could be out there, for sure. But if they are, it's been hard to find them. And if they found us, they are being very discreet. Or just don't care. Either because their psychology is such that they don't have an interest in life elsewhere, or because they don't have a psychology to speak of. Amoeba-like ETs are much more likely than wise, spiritual creatures. But the silence kills, right? We want to know, either way.

Now we can be very excited about the new discovery from NASA's Kepler satellite team, a truly remarkable achievement. They've found not only a system of five planets orbiting a star with mass about half that of the sun but, and here is the punch line, with one of these planets, Kepler-186f, within the so-called "habitable zone" of the star.

NASA's Kepler Discovers First Earth-Size Planet In The Habitable Zone of Another Star

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The habitable zone of a planetary system is the band within which, if a planet belongs there and if it has water and if its atmosphere allows, the water will be liquid on the surface. And liquid water is, at least as we understand it, essential for life. (I wrote about this last week.) So, the discovery of Kepler-186f is a proof of concept: we now know that there are Earth-like planets within the habitable zones of other stars. This is huge.

Kepler-186f is the closest we've come to finding a terrestrial planet that is a cousin of our own: similar mass, radius and with the possibility of liquid water. The system is 500 light-years from Earth in the constellation of Cygnus. This means that what we see now is what the system looked like 500 years ago. The skies are a huge time machine.

Interesting to think that if they been watching us from close up, they'd see large galleons crossing oceans and, if they could find out about our (Western) culture, they'd see people that believed the Earth stood still in the center of the cosmos. Five hundred years ago, the thought of searching for life on another planet would probably take you to the stake. Now we are pursuing it. Kepler, who wrote one of the first — if not the first — sci-fi tale of extraterrestrial life, his Somnium, from 1629, would be very proud.

You can keep up with more of what Marcelo is thinking on Facebook and Twitter: @mgleiser

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