An artist's concept depicts one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of star that is similar to our sun in this NASA image released on July 23, 2015. [Photo/Agencies]

Scientists previously have found Earth-sized planets orbiting in stars' so-called "habitable zones," but those stars are cooler and smaller than the sun, a G2 type yellow star.

NASA launched the Kepler telescope in 2009 to survey a sampling of nearby stars in an attempt to learn if planets like Earth were common in the galaxy.

"This is great progress in finding a planet like Earth that is similar in size and temperature around a sun-like star," said Kepler scientist Jeff Coughlin, with the SETI Institute in Mountain View, California.

Based on its size, scientists believe Kepler-452b should be rocky, like the Earth, though that theory is based on statistical analysis and computer modeling, not direct evidence.

"With a radius 60 percent larger than the Earth, this planet has a somewhat better than even chance of being rocky," Jenkins said.

If so, Kepler-452b could be about five times as massive as Earth and have gravity that is twice as strong as what exists on Earth's surface. The planet also could have a thick atmosphere, cloudy skies and active volcanoes, Jenkins said.

With the discovery of Kepler-452b, the telescope has found 1,030 confirmed planets and identified about 4,700 candidate planets. The list of potential planets includes 11 other near-Earth twins, nine of which circle sun-like stars.

The telescope cannot see planets directly, but measures minute changes in light coming from target stars. Sophisticated computer programs and follow-up observations with a ground-based telescopes then determine if some of the light dips were caused by planets passing in front of their parent stars, relative to Kepler's line of sight.

A positioning system failure ended the telescope's prime planet-hunting mission in 2013, but it has since been repurposed for other astronomical observations.

Attempts to learn if Kepler-452b has an atmosphere likely will have to wait for a new generation of more sensitive space telescopes, said NASA's associate administrator John Grunsfeld.

The research will be published in The Astronomical Journal.