This Is Big: Scientists Just Found Earth's First Cousin

Meet Kepler-186f, the closest thing to our planet ever discovered—and maybe our best shot at locating life elsewhere in the universe. 

Right now, 500 light years away from Earth, there's a planet that looks a lot like our own. It is bathed in dim orangeish light, which at high noon is only as bright as the golden hour before sunset back home.

NASA scientists are calling the planet Kepler-186f, and it's unlike anything they've found. The big news: Kepler-186f is the closest relative to the Earth that researchers have discovered.

It's the first Earth-sized planet in the habitable zone of another star—the sweet spot between too-hot Mercury-like planets and too-cold Neptunes— and it is likely to give scientists their first real opportunity to seek life elsewhere in the universe. "It's no longer in the realm of science fiction," said Elisa Quintana, a researcher at the SETI Institute.

But if there is indeed life on Kepler-186f, it may not look like what we have here. Given the redder wavelengths of light on the planet, vegetation there would sprout in hues of yellow and orange instead of green.

"It's perhaps more like Earth's cousin than Earth's twin," said Tom Barclay, a NASA researcher who spoke about the finding in conference call with reporters.

For decades, scientists have looked for signs of life by scanning space for patterns that could be the imprints of distant technology or natural clues that demonstrate a living planet.

"They're looking for radio signals, some kind of beacon from the star," said Victoria Meadows of the NASA Astrobiology Institute. "If you're talking about life that doesn't have technology on the surface, we look for biosignatures... like gases in the atmosphere that seem to have a constant flux from the surface. We'd look for things like oxygen from photosynthesis."

Kepler-186f is about 10 percent larger than Earth and it orbits a sun that is cooler, dimmer, and about half the size of our own. The effects of gravity would be "slightly" more apparent there, so "you would feel heavier," Meadows said.

Our cousin avoids many of the problems that reduce the likelihood of life on other Earth-like planets. Some are too big, too cold, too gaseous, or have gravity problems that scorch oceans. So far, Kepler-186f appears almost to be a Goldilocks — not too big, not too far from its star, maybe just right.

The planet has a shorter year than we do, orbiting its star once every 130 days. On Earth, of course, we take 365 days to make it around the sun. (Though that hasn't always been the case. Scientists believe that something like 380 million years ago, there were 410 days in an Earth year.)

Researchers aren't yet sure what Kepler-186f is made of, but given its size and other characteristics, they think it's a rocky combo like Earth. (It could be pure iron or frozen in Hoth-like ice, too, though.)

A mission to learn more is in the works. The first step will be attempting to characterize the planet's atmosphere, beginning with determining that it has one.

We may not find life on Kepler-186f, but scientists are confident we could find signs on planets just like it. This is a staggering prospect because of just how many planets like Kepler-186f are out there—so many that scientists are hesitant to even offer ballpark figures. Much closer to us, there are a "huge" number of them, Barclay said.

Today we know that Earth is special. What we don't know is how long we'll be able to say that.