"Super Earth" cousin is closest yet to a world like ours
Analysis of data from NASA's planet-hunting Kepler space telescope has revealed a near Earth-size world orbiting in the habitable zone of a sun-like star, scientists announced Thursday, the closest match yet in the ongoing hunt for planets similar in size to Earth where life, as humans understand it, might have a chance to evolve.
The planet, known as Kepler-452b, orbits a yellow G2-type star some 1,400 light years away in the constellation Cygnus, taking 385 days to complete one trip around its sun. The planet's radius is 60 percent larger than Earth's and depending on its composition, it's possibly up to five times more massive.
And its star is thought to be about six billion years old, 1.5 billion years older than the sun. In keeping with current models of stellar evolution, the star is about 20 percent brighter and 10 percent bigger than the sun, roughly matching what Earth can expect as its star ages, consumes its nuclear fuel and burns hotter in its old age.
While the newly discovered planet is more of a "super Earth" than a twin, it is the first roughly Earth-class planet found in the habitable zone of a sun-like star where the space environment is similar to Earth's and where water can pool on the surface.
"The star has the same surface temperature and type as the sun, a G2 star," Jon Jenkins, the lead Kepler data analyst at NASA's Ames Research Center, said during a teleconference with reporters. "This planet orbits its star every 385 days, and it's just 5 percent farther from its star than the Earth. Now with a radius 60 percent larger than the Earth, this planet has a somewhat better than even chance of being rocky."
If so, he said, "it would likely have a mass about five times that of Earth and a surface gravity of about twice that of Earth. You and I would weigh twice as much as we do now. ... We would also expect the atmosphere to be thicker. This planet likely would still have very active volcanos."
And because Kepler-452b has been orbiting in the habitable zone of its star for more than a billion years longer than Earth, it's had even more time to cook up life if the right mixture of organic compounds, water and sunlight were present.
"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," Jenkins said in a NASA statement. "It's awe-inspiring to consider that this planet has spent six billion years in the habitable zone of its star. That's substantial opportunity for life to arise, should all the necessary ingredients and conditions for life exist on this planet."
Speaking to reporters, he described Kepler-452b as "the closest thing that we have to another place that somebody else might call home."
Launched in March 2009, the Kepler spacecraft was equipped with a 95-megapixel camera that was aimed at a patch of sky the size of an out-stretched hand that contains more than 4.5 million detectable stars. Kepler monitored the light from 160,000 of those suns.
The camera cannot directly "see" exoplanets, but if a planet passes in front of a star as viewed from the space telescope, the star's light will periodically dim as the planet swings through its orbit. By precisely measuring those tiny brightness fluctuations, Kepler researchers can indirectly confirm a planet's presence, size and distance from its sun.
Kepler completed its primary three-year mission in November 2012. NASA managers promptly approved a four-year mission extension, but in 2013, the spacecraft was hobbled by the failure of a second gyro stabilizer, forcing engineers to devise alternative methods of detection. The spacecraft remains in operation and is the most successful planet finder ever built.
Over the first four years of its mission, Kepler's observations allowed researchers to confirm 950 actual exoplanets with another 3,800 "candidate" worldsrequiring additional analysis. The total number of candidates now stands at 4,696, including 521 that were just added to the list. Kepler has now found more than 1,000 confirmed exoplanets.
Of the new candidates, 12 have diameters between one and two times that of Earth and orbit within their star's habitable zone. Of those 12, nine orbit stars similar in size and temperature to the sun.
"We can say near-Earth-size planets in the habitable zone of sun-like stars are common throughout the galaxy," Jenkins said. "Surely there are more gems like 452b waiting to be discovered in the rich Kepler legacy archive."
