An international group of astronomers using NASA’s Kepler Space Telescope has discovered three so-called super-Earth exoplanets orbiting a red dwarf star called EPIC 201367065.
EPIC 201367065 (also catalogued as UCAC4 443-054906) is a red M-dwarf about half the size and mass of our Sun. It lies at a distance of 147 light-years.
The star ranks among the top 10 nearest stars known to have planets. Its 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.
The three exoplanets are 2.1, 1.7 and 1.5 times the size of Earth.
The smallest and outermost planet, EPIC 201367065d, orbits on the edge of the so-called habitable zone, where the temperature may be just right for liquid water, believed necessary to support life, on the planet’s surface. According to the astronomers, the planet has an Earth Similarity Index of 0.80.
In order from farthest to closest to their star, the exoplanets receive 10.5, 3.2 and 1.4 times the light intensity of Earth.
“The compositions of these newfound planets are unknown. There is a very real possibility that the outer planet is rocky like Earth. If so, this planet could have the right temperature to support liquid water oceans,” said Erik Petigura, a graduate student at the University of California, Berkeley, a co-author of the paper submitted for publication in the Astrophysical Journal (arXiv.org preprint).
“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 lead author Dr Ian Crossfield of the University of Arizona.
The discovery is all the more remarkable because Kepler, launched in 2009, is now hobbled by the loss of two reaction wheels that kept it pointing at a fixed spot in space. It was reborn in 2014 as ‘K2’ with a clever strategy of pointing the telescope in the plane of the Earth’s orbit to stabilize the spacecraft.
After the astronomers found the planets around EPIC 201367065 in the Kepler light curves, they quickly employed telescopes in Chile, Hawaii and California to characterize the star’s mass, radius, temperature and age.
The next step will be observations with other telescopes, including Hubble, 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.