PASADENA, Calif. -- NASA's Kepler mission scientists have discovered a
new planetary system that is home to the smallest planet yet found
around a star similar to our sun.
The planets are located in a system called Kepler-37, about 210
light-years from Earth in the constellation Lyra. The smallest planet,
Kepler-37b, is slightly larger than our moon, measuring about one-third
the size of Earth. It is smaller than Mercury, which made its detection a
challenge.
The moon-size planet and its two companion planets were found by
scientists with NASA's Kepler mission, which is designed to find
Earth-sized planets in or near the "habitable zone," the region in a
planetary system where liquid water might exist on the surface of an
orbiting planet. However, while the star in Kepler-37 may be similar to
our sun, the system appears quite unlike the solar system in which we
live.
Astronomers think Kepler-37b does not have an atmosphere and cannot
support life as we know it. The tiny planet almost certainly is rocky in
composition. Kepler-37c, the closer neighboring planet, is slightly
smaller than Venus, measuring almost three-quarters the size of Earth.
Kepler-37d, the farther planet, is twice the size of Earth.
The first exoplanets found to orbit a normal star were giants. As
technologies have advanced, smaller and smaller planets have been found,
and Kepler has shown that even Earth-size exoplanets are common.
"Even Kepler can only detect such a tiny world around the brightest
stars it observes," said Jack Lissauer, a planetary scientist at NASA's
Ames Research Center in Moffett Field, Calif. "The fact we've discovered
tiny Kepler-37b suggests such little planets are common, and more
planetary wonders await as we continue to gather and analyze additional
data."
Kepler-37's host star belongs to the same class as our sun, although it
is slightly cooler and smaller. All three planets orbit the star at less
than the distance Mercury is to the sun, suggesting they are very hot,
inhospitable worlds. Kepler-37b orbits every 13 days at less than
one-third Mercury's distance from the sun. The estimated surface
temperature of this smoldering planet, at more than 800 degrees
Fahrenheit (700 degrees Kelvin), would be hot enough to melt the zinc in
a penny. Kepler-37c and Kepler-37d, orbit every 21 days and 40 days,
respectively.
"We uncovered a planet smaller than any in our solar system orbiting one
of the few stars that is both bright and quiet, where signal detection
was possible," said Thomas Barclay, Kepler scientist at the Bay Area
Environmental Research Institute in Sonoma, Calif., and lead author of
the new study published in the journal Nature. "This discovery shows
close-in planets can be smaller, as well as much larger, than planets
orbiting our sun."
The research team used data from NASA's Kepler space telescope, which
simultaneously and continuously measures the brightness of more than
150,000 stars every 30 minutes. When a planet candidate transits, or
passes, in front of the star from the spacecraft's vantage point, a
percentage of light from the star is blocked. This causes a dip in the
brightness of the starlight that reveals the transiting planet's size
relative to its star.
The size of the star must be known in order to measure the planet's size
accurately. To learn more about the properties of the star Kepler-37,
scientists examined sound waves generated by the boiling motion beneath
the surface of the star. They probed the interior structure of
Kepler-37's star just as geologists use seismic waves generated by
earthquakes to probe the interior structure of Earth. The science is
called asteroseismology.
The sound waves travel into the star and bring information back up to
the surface. The waves cause oscillations that Kepler observes as a
rapid flickering of the star's brightness. Like bells in a steeple,
small stars ring at high tones while larger stars boom in lower tones.
The barely discernible, high-frequency oscillations in the brightness of
small stars are the most difficult to measure. This is why most objects
previously subjected to asteroseismic analysis are larger than the sun.
With the very high precision of the Kepler instrument, astronomers have
reached a new milestone. The star Kepler-37, with a radius just
three-quarters of the sun, now is the smallest bell in the
asteroseismology steeple. The radius of the star is known to three
percent accuracy, which translates to exceptional accuracy in the
planet's size.
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 tenth Discovery
Mission and was funded by NASA's Science Mission Directorate at the
agency's headquarters in Washington.
For more information about the Kepler mission, visit: http://www.nasa.gov/kepler .
Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov
J.D. Harrington 202-358-5241
Headquarters, Washington
j.d.harrington@nasa.gov
