The
artist's concept depicts Kepler-186f , the first validated Earth-size
planet to orbit a distant star in the habitable zone. Image Credit: NASA Ames/SETI Institute/JPL-Caltech. Kepler-186f, the first Earth-size Planet in the Habitable Zone
The
diagram compares the planets of our inner solar system to Kepler-186, a
five-planet star system about 500 light-years from Earth in the
constellation Cygnus. The five planets of Kepler-186 orbit an M dwarf, a
star that is is half the size and mass of the sun. Image Credit: NASA Ames/SETI Institute/JPL-Caltech. Kepler-186 and the Solar System
Using
NASA's Kepler Space Telescope, astronomers have discovered the first
Earth-size planet orbiting a star in the "habitable zone" -- the range
of distance from a star where liquid water might pool on the surface of
an orbiting planet. The discovery of Kepler-186f confirms that planets
the size of Earth exist in the habitable zone of stars other than our
sun.
While planets have previously been found in the habitable zone, they
are all at least 40 percent larger in size than Earth and understanding
their makeup is challenging. Kepler-186f is more reminiscent of Earth.
"The discovery of Kepler-186f is a significant step toward finding
worlds like our planet Earth," said Paul Hertz, NASA's Astrophysics
Division director at the agency's headquarters in Washington. "Future
NASA missions, like the Transiting Exoplanet Survey Satellite and the
James Webb Space Telescope, will discover the nearest rocky exoplanets
and determine their composition and atmospheric conditions, continuing
humankind's quest to find truly Earth-like worlds."
Although the size of Kepler-186f is known, its mass and composition
are not. Previous research, however, suggests that a planet the size of
Kepler-186f is likely to be rocky.
"We know of just one planet where life exists -- Earth. When we
search for life outside our solar system we focus on finding planets
with characteristics that mimic that of Earth," said Elisa Quintana,
research scientist at the SETI Institute at NASA's Ames Research Center
in Moffett Field, Calif., and lead author of the paper published today
in the journal Science. "Finding a habitable zone planet comparable to
Earth in size is a major step forward."
Kepler-186f resides in the Kepler-186 system, about 500 light-years
from Earth in the constellation Cygnus. The system is also home to four
companion planets, which orbit a star half the size and mass of our sun.
The star is classified as an M dwarf, or red dwarf, a class of stars
that makes up 70 percent of the stars in the Milky Way galaxy.
"M dwarfs are the most numerous stars," said Quintana. "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
one-third the energy from its star that Earth gets from the sun, placing
it nearer the outer edge of the habitable zone. On the surface of
Kepler-186f, the brightness of its star at high noon is only as bright
as our sun appears to us about an hour before sunset.
"Being in the habitable zone does not mean we know this planet is
habitable. The temperature on the planet is strongly dependent on what
kind of atmosphere the planet has," said Thomas Barclay, research
scientist at the Bay Area Environmental Research Institute at Ames, and
co-author of the paper. "Kepler-186f can be thought of as an
Earth-cousin rather than an Earth-twin. It has many properties that
resemble Earth."
The four companion planets, Kepler-186b, Kepler-186c, Kepler-186d,
and Kepler-186e, whiz around their sun every four, seven, 13, and 22
days, respectively, making them too hot for life as we know it. These
four inner planets all measure less than 1.5 times the size of Earth.
The next steps in the search for distant life include looking for
true Earth-twins -- Earth-size planets orbiting within the habitable
zone of a sun-like star -- and measuring the their chemical
compositions. The Kepler Space Telescope, which simultaneously and
continuously measured the brightness of more than 150,000 stars, is
NASA's first mission capable of detecting Earth-size planets around
stars like our sun.
Ames is responsible for Kepler's ground system development, mission
operations, and science data analysis. NASA's Jet Propulsion Laboratory
in Pasadena, Calif., managed Kepler mission development. Ball Aerospace
& Technologies Corp. in Boulder, Colo., developed the Kepler flight
system and supports mission operations with the Laboratory for
Atmospheric and Space Physics at the University of Colorado in Boulder.
The Space Telescope Science Institute in Baltimore archives, hosts and
distributes Kepler science data. Kepler is NASA's 10th Discovery Mission
and was funded by the agency's Science Mission Directorate.
The SETI Institute is a private, nonprofit organization dedicated to
scientific research, education and public outreach. The mission of the
SETI Institute is to explore, understand and explain the origin, nature
and prevalence of life in the universe.
For more information about the Kepler mission, visit: http://www.nasa.gov/kepler
Media contacts:
Michele Johnson
Ames Research Center, Moffett Field, Calif.
650-604-6982
michele.johnson@nasa.gov
J.D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington@nasa.gov
