Illustration Credit: NASA Ames / SETI Institute / JPL-Caltech, Discovery: Elisa V. Quintana, et al.
Explanation: Planet
Kepler-186f is the first known Earth-size planet to lie within the habitable zone of a star beyond the Sun. Discovered using data
from the prolific planet-hunting Kepler
spacecraft, the distant world orbits its parent star, a cool, dim, M dwarf
star about half the size and mass of the Sun, some 500 light-years away in the
constellation Cygnus. M dwarfs are common,
making up about 70 percent of the stars in our Milky Way galaxy. To be within the habitable zone, where surface temperatures allowing
liquid water are possible, Kepler-186f
orbits close, within 53 million kilometers (about the Mercury-Sun distance)
of the M dwarf star, once every 130 days. Four other planets are known in the
distant system. All four are only a little larger than Earth and in much closer
orbits, also illustrated in the tantalizing artist's vision. While the size and
orbit of Kepler-186f are known, its mass and composition are not, and can't be
determined by Kepler's transit technique. Still,
models suggest that it could be rocky and have an atmosphere, making it potentially the most Earth-like exoplanet discovered so far
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