The Kepler space telescope has discovered a star with three earth-like planets slightly larger in size than Earth at a distance of 150 light years.
The star, EPIC 201367065, is a cool red M-dwarf about half the size and mass of our own Sun and it ranks among the top 10 nearest stars known to have transiting planets.
“A thin atmosphere made of nitrogen and oxygen has allowed life to thrive on Earth. But nature is full of surprises. Many exoplanets discovered by the Kepler mission are enveloped by thick, hydrogen-rich atmospheres that are probably incompatible with life as we know it,” said Ian Crossfield, the University of Arizona astronomer.
“Most planets we have found to date are scorched. This system is the closest star with lukewarm transiting planets,” added University of California Berkeley graduate student Erik Petigura.
Petigura discovered the planets on January 6 while conducting a computer analysis of the Kepler data NASA has made available to astronomers.
“There is a very real possibility that the outermost planet is rocky like Earth, which means this planet could have the right temperature to support liquid water oceans,” he noted.
After Petigura found the planets in the Kepler light curves, the team quickly employed telescopes in Chile, Hawaii and California to characterise the star’s mass, radius, temperature and age.
The star’s proximity means it is bright enough for astronomers to study the planets’ atmospheres to determine whether they are like the Earth’s atmosphere and possibly conducive to life.
The next step will be observations with other telescopes, including the Hubble Space Telescope, to take the spectroscopic fingerprint of the molecules in the planetary atmospheres.
“If these warm, nearly Earth-size planets have puffy, hydrogen-rich atmospheres, Hubble will see the telltale signal,” Petigura said.
The paper has been submitted to Astrophysical Journal and is freely available on the arXiv website .
Kepler has so far found more than 1,000 verified planets and of them eight are less than twice Earth-size and in their stars’ habitable zone. However, the search continues for Earth-size habitable zone worlds around sun-like stars, said NASA.
“Each result from the planet-hunting Kepler mission’s treasure trove of data takes us another step closer to answering the question of whether we are alone in the Universe,” said John Grunsfeld, associate administrator of NASA’s Science Mission Directorate at the agency’s headquarters in Washington.
To determine whether a planet is made of rock, water or gas, scientists must know its size and mass. When its mass can’t be directly determined, scientists can infer what the planet is made of based on its size.
Two of the newly validated planets, Kepler-438b and Kepler-442b, are less than 1.5 times the diameter of Earth. Kepler-438b, 475 light-years away, is 12 percent bigger than Earth and orbits its star once every 35.2 days. Kepler-442b, 1,100 light-years away, is 33 percent bigger than Earth and orbits its star once every 112 days.
Both Kepler-438b and Kepler-442b orbit stars smaller and cooler than our sun, making the habitable zone closer to their parent star, in the direction of the constellation Lyra. The research paper reporting this finding has been accepted for publication in The Astrophysical Journal.
“Kepler collected data for four years — long enough that we can now tease out the Earth-size candidates in one Earth-year orbits”, said Fergal Mullally, SETI Institute Kepler scientist at Ames who led the analysis of a new candidate catalog. “We’re closer than we’ve ever been to finding Earth twins around other sun-like stars. These are the planets we’re looking for”.