Since its inception in Spring 2009, NASA’s Kepler Space Telescope has been hunting exoplanets, or planets outside the Solar System, the holy grail being a planet similar to ours in terms of size, composition, and habitability. In its mission, Kepler utilizes the transit method: it continuously measures the brightness of 150,000 stars, looking for dips in the amount of light received from each star. The idea is that if a star has planets, then every time the planet passes between us and its parent star, it will block a very small amount of light (usually less than one percent).
Kepler has now confirmed the existence of an Earth-sized exoplanet in its star’s habitable zone, or “Goldilocks zone,” the range of distance from a star where liquid water might pool on the surface of an orbiting planet. The announcement was made during a press conference earlier today, and the findings have been published in Science. The discovery of this exoplanet, called Kepler-186f, confirms that planets the size of Earth exist in the habitable zone of stars other than our sun.
Kepler-186f, is about 10% larger than Earth, and orbits an M-dwarf star half the size and mass of our sun some 500 light years away in the constellation Cygnus. M dwarfs, or red dwarfs, make up 70% of the stars in the Milky Way galaxy. Elisa Quintana, research scientist at the SETI Institute at NASA’s Ames Research Center and lead author of the paper published in Science today, said, “M dwarfs are the most numerous stars. The first signs of other life in the galaxy may well come from planets orbiting an M dwarf.”
Kepler-186f orbits its star once every 130 days and receives about one-third the energy from its star that Earth gets from the sun, placing it near the outer edge of the habitable zone. Thomas Barclay, research scientist at the Bay Area Environmental Research Institute at Ames and co-author of the paper, notes,
“Being in the habitable zone does not mean we know this planet is habitable. The temperature of the planet is strogly dependent on what kind of atmosphere the planet has. Kepler-186f can be thought of as an Earth-cousin rather than an Earth-twin. It has many properties that resemble Earth.”