Scientists on the hunt for extraterrestrial life have discovered “the closest twin to Earth” outside the solar system, Nasa announced on Thursday.
Working off four years’ worth of data from the Kepler space telescope, researchers from Nasa, the Seti Institute and several universities announced the new exoplanet along with 12 possible “habitable” other exoplanets and 500 new candidates in total.
The new planet, named Kepler 452b, is “the closest twin to Earth, or the Earth 2.0 that we’ve found so far in the dataset”, said John Grunsfeld, associate administrator for Nasa’s mission directorate.
“This is the first possibly rocky, habitable planet around a solar-type star,” said Jeff Coughlin, a Seti scientist. All 11 previously discovered exoplanets of a similar size and orbit travel around stars that are smaller and cooler than the sun.
“It is the closest thing that we have to another place that somebody might call home,” said Jon Jenkins, a Nasa scientist. The planet is like Earth’s “older, bigger first cousin”, he said.
The research suggests 452b has five times the mass of Earth, is about 1.5bn years older, and has a gravity about twice as powerful as our own.
About 1,400 light years away, Kepler 452b orbits a star similar to our sun, and at about the same distances as Earth orbits the sun, meaning it has a similar length year and exists in the “habitable zone” where liquid water can exist on a planet.
Jenkins said they suspect the planet is rocky, likely with active volcanoes, and has a thicker atmosphere with greater cloud cover than the Earth.
But although 452b has more in common with Earth than any exoplanet yet discovered, its star is 1.5bn years older, 4% more massive and 20% brighter than our own. As stars age they grow in size and energy, casting more heat at the objects in their orbit.
Jenkins compared them to people. “When they’re young they’re small and dim,” he said, and millennia later “they grow and they get brighter”.
The new planet consequently receives 10% more energy than the Earth, meaning it could provide a glimpse into a burning, waterless future on Earth, the scientists said.
“Kepler 452b could be experiencing now what the Earth will undergo more than a billion years from now,” said Doug Caldwell, a Seti Institute scientist on the Kepler mission.
“If Kepler 452b is indeed a rocky planet,” he said, its location “could mean that it is just entering a runaway greenhouse phase of its climate history. Its ageing sun might be heating the surface and evaporating any oceans. The water vapor would be lost from the planet forever.”
The scientists also found 11 other possible exoplanets that might be less than twice the Earth’s diameter and orbiting in habitable zones. Seven candidates appear to orbit solar-type stars, Coughlin said. “Time will tell if they stand the tests.”
The discovery “takes us one step closer to understanding how many habitable planets are out there”, said Joseph Twicken, a Seti scientist also on the Kepler mission.
Coughlin said that sifting through the catalog will help astronomers “determine the number of small, cool planets that are the best candidates for hosting life”.
“We’re trying to answer really fundamental questions,” Grunsfeld said. “Where are we going as human beings, and of course the really grand question: are we alone in the universe?”
The Kepler telescope can find possible planets by detecting tiny changes in the brightness of stars as planets pass between them and Earth. The researchers will have to use other techniques, such as looking for shifts in the motion of other suns, to verify the nature of the objects.
Of the 4,661 exoplanet candidates catalogued by the Kepler mission, 1,028 have been confirmed. Eleven of those are confirmed exoplanets less than twice Earth’s size and in the habitable zone of their stars. The first exoplanet orbiting a distant star was discovered in 1995.
The Kepler space telescope identifies possible planets by observing periodic dips in the brightness of stars as planets pass before them, in the same way the moon causes an eclipse on Earth. However, confirmation of their true planetary status requires observations by other instruments, typically looking for slight shifts in the motion of the host suns.
In 2017 Nasa plans to launch the successor to the Kepler mission, a survey satellite that searches the nearest solar systems for exoplanets. Grunsfeld said that with increasingly powerful telescopes and satellites, scientists may someday be able to “make the first primitive maps of an Earth-like planet”, including details of “whether they have oceans, clouds, perhaps even seasons”.
Cambridge professor Didier Queloz said the team has only reasons to be optimistic for planets that resemble Earth even more closely: “This is just the beginning of a very long journey.”
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