NASA Finds the Most Earth-Like Exoplanet Yet

NASA has discovered the closest thing yet to another Earth, scientists announced in a press conference Thursday. The exoplanet is named Kepler-452b, and it's the first near-Earth-sized planet found orbiting in the "habitable zone" of a sun-like star.

The habitable zone is the area around a star where liquid water can pool on the surface of an orbiting planet, potentially enabling life as we know it. Scientists can't be sure yet if Kepler-452b has a rocky surface — not to mention water — but so far it looks more like our home world than any previously discovered exoplanet.

Kepler-452b is about 60 percent larger than Earth in diameter, but it's the smallest-known planet in the habitable zone of a G2-type star, like our sun. Its mass and makeup are still unclear, but scientists with NASA's Kepler Mission say it's probably about five times Earth's mass with roughly double our planet's gravity. It has a "slightly better than even chance of being rocky," its discoverers say.

This exoplanet's home star, Kepler-452, is similar to our sun but with a few key differences. It's 1.5 billion years older, 20 percent brighter and 10 percent larger in diameter. It's about the same temperature, though, and Kepler-452b is only 5 percent farther away from it than we are from our sun.

Kepler-452b's orbit is similar to Earth's, sending the planet around its star once every 385 days. (Image: NASA/R. Hurt)

"We can think of Kepler-452b as an older, bigger cousin to Earth, providing an opportunity to understand and reflect upon Earth's evolving environment," Jon Jenkins, who led the team that discovered Kepler-452b, says in a statement. "It's awe-inspiring to consider that this planet has spent 6 billion years in the habitable zone of its star; longer than Earth. That's substantial opportunity for life to arise, should all the necessary ingredients and conditions for life exist on this planet."

Kepler-452 is 1,400 light-years away from Earth in the constellation Cygnus, NASA notes, so no humans will visit anytime soon. But finding such a seemingly hospitable planet bodes well for the existence of others, especially since we now know planets are far more common than we thought just a few decades ago.

"Most of the stars we see in the night sky have solar systems around them," NASA associate administrator John Grunsfeld said Thursday. "Surely there are more gems like Kepler-452b waiting to be discovered," Jenkins added.

The blue dots show planet candidates from previous Kepler catalogs; the yellow dots are new. (Image: NASA/W. Stenzel)

And as both researchers emphasized, we have good reason to be excited about actually finding those gems. The first confirmation of an extrasolar planet didn't come until 1994, and since then we've been discovering them in droves — especially after the launch of the exoplanet-hunting Kepler mission in 2009.

Kepler has now confirmed more than 1,000 exoplanets, along with nearly 4,700 others awaiting confirmation. In fact, on top of Kepler-452b, NASA's newfound batch also includes 11 other habitable-zone candidates with sizes possibly conducive to life. And while scientists are still examining data Kepler has already collected, NASA is planning to launch a new planet hunter in 2017. Named Transiting Exoplanet Survey Satellite (TESS), it will spend two years monitoring more than 500,000 stars, looking for brief drops in brightness caused by a potential planet passing by.

"This is a fortunate time to be living," University of Cambridge astrophysicist Didier Queloz said Thursday. "This is not sci-fi anymore."