NASA’s Kepler Space Telescope, despite being hobbled by the loss of critical guidance systems, has discovered a star with three planets only slightly larger than Earth.The outermost planet orbits in the “Goldilocks” zone, a region where surface temperatures could be moderate enough for liquid water and perhaps life, to exist.
The star, EPIC 201367065, is a cool red M-dwarf about half the size and mass of our own sun. At a distance of 150 light years, the star ranks among the top 10 nearest stars known to have transiting planets. The star’s proximity means it’s bright enough for astronomers to study the planets’ atmospheres to determine whether they are like Earth’s atmosphere and possibly conducive to life.
“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 who led the study.
The three planets are 2.1, 1.7 and 1.5 times the size of Earth. The smallest and outermost planet, at 1.5 Earth radii, orbits far enough from its host star that it receives levels of light from its star similar to those received by Earth from the sun, said UC Berkeley graduate student Erik Petigura. He discovered the planets Jan. 6 while conducting a computer analysis of the Kepler data NASA has made available to astronomers. In order from farthest to closest to their star, the three planets receive 10.5, 3.2 and 1.4 times the light intensity of Earth, Petigura calculated.
“Most planets we have found to date are scorched. This system is the closest star with lukewarm transiting planets,” Petigura said. “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.”
“We’ve learned in the past year that planets the size and temperature of Earth are common in our Milky Way galaxy,” Howard said. “We also discovered some Earth-size planets that appear to be made of the same materials as our Earth, mostly rock and iron.”
This work has been submitted to Astrophysical Journal and is freely available on the arXiv website.