Astronomers discover most Earth-like planet yet

By Irene Klotz
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Kepler-452b

This 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. (NASA/JPL-Caltech/T. Pyle) This 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. The habitable zone is a region around a star where temperatures are right for water -- an essential ingredient for life as we know it -- to pool on the surface. Scientists do not know if Kepler-452b can support life or not. What is known about the planet is that it is about 60 percent larger than Earth, placing it in a class of planets dubbed "super-Earths." While its mass and composition are not yet determined, previous research suggests that planets the size of Kepler-452b have a better than even chance of being rocky. Kepler-452b orbits its star every 385 days. The planet's star is about 1,400 light-years away in the constellation Cygnus. It is a G2-type star like our sun, with nearly the same temperature and mass. This star is 6 billion years old, 1.5 billion years older than our sun. As stars age, they grow in size and give out more energy, warming up their planets over time.

By Irene Klotz

CAPE CANAVERAL, Fla. (Reuters) - A planet believed to be remarkably similar to Earth has been discovered orbiting a distant sun-like star, bolstering hopes of finding life elsewhere in the universe, U.S. scientists said on Thursday.

The planet, which is about 60 percent bigger than Earth, is located 1,400 light years away in the constellation Cygnus. It was discovered by astronomers using NASA’s Kepler space telescope and circles a star that is similar in size and temperature to the sun, but older.

“In my mind, this is the closest thing we have to another planet like the Earth,” astronomer Jon Jenkins, with the U.S. space agency's Ames Research Center in Moffett Field, California, told reporters on a conference call. The planet, dubbed Kepler-452b, orbits a star that is about 6 billion years old, compared to the 4.6 billion year age of the sun. “It’s simply awe-inspiring to consider that this planet has spent 6 billion years in the habitable zone of its star,” Jenkins said.

“That’s considerable time and opportunity for life to arise somewhere on its surface or in its oceans should all the necessary ingredients and conditions for life exist on this planet,” he said.

Kepler-452b is positioned about as far from its parent star as Earth is from the sun, completing an orbit in 385 days, compared to Earth’s 365-day orbit. At that distance, surface temperatures would be suitable for liquid water, a condition believed to be critical for life. 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.

(Reporting by Irene Klotz; Editing by David Adams and Tom Brown)