New Discovery in the Hunt for Earth-Like Planets

7-23-15 Kepler-452b and Earth
This artist's concept compares Earth, left, to the new planet, called Kepler-452b, which is about 60 percent larger in diameter. NASA/JPL-Caltech/T. Pyle

We are one step closer to answering the grand question of whether or not we're alone in the universe, NASA announced in a news conference Thursday. The agency presented the discovery of the first planet roughly the size of Earth orbiting a G2-type star, which is similar to our sun. That solar system is 1,400 light-years away in a constellation called Cygnus.

"On the 20th anniversary year of the discovery that proved other suns host planets, the Kepler exoplanet explorer has discovered a planet and star which most closely resemble the Earth and our Sun," John Grunsfeld, associate administrator of NASA's Science Mission Directorate, is quoted as saying. "This exciting result brings us one step closer to finding an Earth 2.0."

The newly discovered exoplanet—a planet that orbits around a star other than the sun (also called extrasolar planet)—is called Kepler-452b. The diameter of Kepler-452b is 60 percent larger than that of Earth, and NASA says it's likely rocky. Its 385-day orbit around its star is just 5 percent longer than that of Earth, and it's located just 5 percent farther from its star, Kepler-452, than Earth is from the sun. At 6 billion years old, Kepler-452 is 1.5 billion years older than our sun. It's also 20 percent brighter, and with a diameter larger by 10 percent. Still, it has the same temperature as our sun.

"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," said Jon Jenkins, the Kepler data analysis lead at NASA's Ames Research Center in Moffett Field, California. "It's awe-inspiring to consider that this planet has spent 6 billion years in the habitable zone of its star; longer than Earth," he added. "That's substantial opportunity for life to arise, should all the necessary ingredients and conditions for life exist on this planet."

The Kepler mission surveys our region of the Milky Way, monitoring stars outside our solar system to try to identify new exoplanets. NASA is particularly interested in identifying planets one half to twice the size of Earth—terrestrial planets rather than the gas or ice giants or hot-super-Earths in short period orbits that evidence suggests exist in large numbers—especially ones that are located in the habitable zone of their stars.

Sometimes referred to as the "Goldilocks" zone by the media and the "surface water liquid zone" by scientists, the habitable zone refers to the range of distance from the star in which a planet orbiting it could have liquid water on its surface. Liquid water means the planet could theoretically support life as we know it.

NASA said Thursday that Kepler-452 is the first near-Earth-size planet to orbit in the habitable zone of a star that's similar in size and temperature to our sun. It also announced 521 new exoplanet candidates that will be added to list in the seventh Kepler Candidate Catalog, making a total of 4,696 candidates detected by the Kepler mission. A dozen of the new candidates have diameters one to two times that of Earth's and nine of those orbit stars similar to our sun in terms of size and temperature.

"Exoplanets, especially small Earth-size worlds, belonged within the realm of science fiction just 21 years ago," reads NASA's press release announcing Thursday's news conference. "Today, and thousands of discoveries later, astronomers are on the cusp of finding something people have dreamed about for thousands of years—another Earth."