(CNN) NASA said Thursday that its Kepler spacecraft has spotted "Earth's bigger, older cousin": the first nearly Earth-size planet to be found in the habitable zone of a star similar to our own.

Though NASA can't say for sure whether the planet is rocky like ours or has water and air, it's the closest match yet found.

This diagram compares the planets of our own inner solar system to Kepler-69, which hosts a planet Kepler-69c that appears to be capable of hosting life, in addition to planet Kepler-69b.

This diagram compares the planets of our own inner solar system to Kepler-69, which hosts a planet Kepler-69c that appears to be capable of hosting life, in addition to planet Kepler-69b.

The planet Kepler-69c is about 2,700 light-years from Earth in the constellation Cygnus.

The planet Kepler-69c is about 2,700 light-years from Earth in the constellation Cygnus.

This diagram compares the planets of our own inner solar system to Kepler-62, a five-planet system about 1,200 light-years from Earth. Kepler-62e and Kepler-62f are thought capable of hosting life.

This diagram compares the planets of our own inner solar system to Kepler-62, a five-planet system about 1,200 light-years from Earth. Kepler-62e and Kepler-62f are thought capable of hosting life.

This illustration depicts Kepler-62f, a planet in the habitable zone of a star smaller and cooler than the sun, in the same system as Kepler-62e.

This illustration depicts Kepler-62f, a planet in the habitable zone of a star smaller and cooler than the sun, in the same system as Kepler-62e.

This illustration depicts Kepler-62e, a planet in the habitable zone of a star smaller and cooler than the sun. It is about 1,200 light-years from Earth in the constellation Lyra.

This illustration depicts Kepler-62e, a planet in the habitable zone of a star smaller and cooler than the sun. It is about 1,200 light-years from Earth in the constellation Lyra.

This diagram lines up planets recently discovered by Kepler in terms of their sizes, compared with Earth. Kepler-22b was announced in December 2011; the three Super-Earths were announced April 18, 2013. All of them could potentially host life, but we do not know anything definitive about their compositions or atmosphere.

This diagram lines up planets recently discovered by Kepler in terms of their sizes, compared with Earth. Kepler-22b was announced in December 2011; the three Super-Earths were announced April 18, 2013. All of them could potentially host life, but we do not know anything definitive about their compositions or atmosphere.

This diagram shows the planets thought to orbit star Gliese 667C, where c, f and e appear to be capable of having liquid water. The relative sizes, but not relative separations, are shown to scale.

This diagram shows the planets thought to orbit star Gliese 667C, where c, f and e appear to be capable of having liquid water. The relative sizes, but not relative separations, are shown to scale.

Scientists announced in June 2013 that three planets orbiting star Gliese 667C could be habitable. This is an artist's impression of the view from one of those planets, looking toward the parent star in the center. The other two stars in the system are visible to the right.

Scientists announced in June 2013 that three planets orbiting star Gliese 667C could be habitable. This is an artist's impression of the view from one of those planets, looking toward the parent star in the center. The other two stars in the system are visible to the right.

A team of astronomers announced April 17, 2014, that they discovered the first Earth-size planet orbiting a star in the "habitable zone": the distance from a star where liquid water might pool on the surface. That doesn't mean this planet has life on it, says Thomas Barclay, a scientist at the Bay Area Environmental Research Institute at Ames and a co-author of a paper on the planet, called Kepler-186f. He says the planet can be thought of as an "Earth-cousin rather than an Earth-twin. It has many properties that resemble Earth." The planet was discovered by NASA's Kepler Space Telescope. It's about 500 light-years from Earth in the constellation Cygnus. The picture above is an artist's concept of what it might look like.

A team of astronomers announced April 17, 2014, that they discovered the first Earth-size planet orbiting a star in the "habitable zone": the distance from a star where liquid water might pool on the surface. That doesn't mean this planet has life on it, says Thomas Barclay, a scientist at the Bay Area Environmental Research Institute at Ames and a co-author of a paper on the planet, called Kepler-186f. He says the planet can be thought of as an "Earth-cousin rather than an Earth-twin. It has many properties that resemble Earth." The planet was discovered by NASA's Kepler Space Telescope. It's about 500 light-years from Earth in the constellation Cygnus. The picture above is an artist's concept of what it might look like.

Kepler-452b is about 60% larger than Earth, left. It's about 1,400 light-years from Earth in the constellation Cygnus.

Kepler-452b is about 60% larger than Earth, left. It's about 1,400 light-years from Earth in the constellation Cygnus.

On Thursday, July 23, NASA announced the discovery of Kepler-452b, "Earth's bigger, older cousin." This artistic concept shows what the planet might look like. Scientists can't tell yet whether Kepler-452b has oceans and continents like Earth.

On Thursday, July 23, NASA announced the discovery of Kepler-452b, "Earth's bigger, older cousin." This artistic concept shows what the planet might look like. Scientists can't tell yet whether Kepler-452b has oceans and continents like Earth.

This artist's impression shows an imagined view from the surface one of the three planets orbiting an ultracool dwarf star just 40 light-years from Earth that were discovered using the TRAPPIST telescope at ESO's La Silla Observatory. Given the proximity of the dwarf star, the rosy sun would appear very large in the sky.

This artist's impression shows an imagined view from the surface one of the three planets orbiting an ultracool dwarf star just 40 light-years from Earth that were discovered using the TRAPPIST telescope at ESO's La Silla Observatory. Given the proximity of the dwarf star, the rosy sun would appear very large in the sky.

The Kepler mission has discovered 1,284 new planets. Of these newly discovered planets, nine orbit in the habitable zone of their star and nearly 550 are possibly rocky planets roughly around the same size as Earth.

The Kepler mission has discovered 1,284 new planets. Of these newly discovered planets, nine orbit in the habitable zone of their star and nearly 550 are possibly rocky planets roughly around the same size as Earth.

"Today, Earth is a little less lonely," Kepler researcher Jon Jenkins said.

The planet, Kepler-452b, is about 1,400 light-years from Earth in the constellation Cygnus. It's about 60% bigger than Earth, NASA says, and is located in its star's habitable zone -- the region where life-sustaining liquid water is possible on the surface of a planet.

A visitor there would experience gravity about twice that of Earth's, and planetary scientists say the odds of it having a rocky surface are "better than even."

While it's a bit farther from its star than Earth is from the sun, its star is brighter, so the planet gets about the same amount of energy from its star as Earth does from the sun. And that sunlight would be very similar to Earth's, Jenkins said.

The planet "almost certainly has an atmosphere," Jenkins said, although scientists can't say what it's made of. But if the assumptions of planetary geologists are correct, he said, Kepler-452b's atmosphere would probably be thicker than Earth's, and it would have active volcanoes.

It takes 385 days for the planet to orbit its star, very similar to Earth's 365-day year, NASA said. And because it's spent so long orbiting in this zone -- 6 billion years -- it's had plenty of time to brew life, Jenkins said.

"That's substantial opportunity for life to arise, should all the necessary ingredients and conditions for life exist on this planet," he said in a statement.

Before the discovery of this planet, one called Kepler-186f was considered the most Earthlike, according to NASA . That planet, no more than a 10th bigger than Earth, is about 500 light-years away from us. But it gets only about a third of the energy from its star as Earth does from the sun, and noon there would look similar to the evening sky here, NASA says.

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The $600 million Kepler mission launched in 2009 with a goal to survey a portion of the Milky Way for habitable planets.

From a vantage point 64 million miles from Earth, it scans the light from distant stars, looking for almost imperceptible drops in a star's brightness, suggesting a planet has passed in front of it.

It has discovered more than 1,000 planets. Twelve of those, including Kepler-425b, have been less than twice the size of Earth and in the habitable zones of the stars they orbit.

Missions are being readied to move scientists closer to the goal of finding yet more planets and cataloging their atmospheres and other characteristics.

In 2017, NASA plans to launch a planet-hunting satellite called TESS that will be able to provide scientists with more detail on the size, mass and atmospheres of planets circling distant stars.

The next year, the James Webb Space Telescope will go up. That platform, NASA says, will provide astonishing insights into other worlds, including their color, seasonal differences, weather and even the potential presence of vegetation.