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Discovery: Kepler-37b, a planet only slightly larger than the Moon
02.20.2013

NASA's Kepler mission has discovered a new planetary system that is home to the smallest planet yet found around a star like our sun, approximately 210 light-years away in the constellation Lyra.

See NASA RELEASE : 13-057.

Diagram of Kepler-37 system.

Is Kepler-37b truly a planet or is it a dwarf planet? The 26th General Assembly of the International Astronomical Union (IAU) defined a planet as “a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.” For exoplanets, part (a) becomes “is in orbit around a star.” So far so good. For the second criterion (b), the Kepler team estimates the mass of Kepler-37b to be greater than 0.01 Earth mass, which is ample mass to insure the body is nearly round. This mass is also sufficient to satisfy the 3rd criterion (c) that the planet clear out lesser bodies in the neighborhood of its orbit. The team therefore confidently concludes that Kepler-37b is truly a planet.

Image credit: NASA/Ames/JPL-Caltech. The line up compares the smallest known planet to the moon and planets in the solar system. Kepler-37b is slightly larger than our moon, measuring about one-third the size of Earth. Kepler-37c, the second planet, is slightly smaller than Venus, measuring almost three-quarters the size of Earth. Kepler-37d, the third planet, is twice the size of Earth.

A "year" on these planets is very short. Kepler-37b orbits its host star every 13 days at less than one-third the distance Mercury is to the sun. The other two planets, Kepler-37c and Kepler-37d, orbit their star every 21 and 40 days. All three planets have orbits lying less than the distance Mercury is to the sun, suggesting that they are very hot, inhospitable worlds.

Many news stories have appeared about the Kepler-37 planet discoveries:
AP: Kepler Telescope Finds Exoplanet About The Size Of The Moon (2/21, Chang) reports scientists using the Kepler telescope data have discovered a planet about the size of the moon, although the exoplanet, called Kepler-37b, "orbits too close to its sun-like star and is too sizzling to support life." It was discovered by Thomas Barclay of the Ames Research Center and it "took more than a year and an international team to confirm that it was a bona fide planet." UC Berkeley's Geoff Marcy said, "This new discovery raises the specter that the universe is jampacked, like jelly beans in a jar, with planets even smaller than Earth." Alan Boss of the Carnegie Institution for Science, called the discovery a "milestone" towards finding an Earth-like planet

Artist's depiction of Kepler-37b.
Image credit: NASA/Ames/JPL-Caltech. The artist's concept depicts the new planet dubbed Kepler-37b, the smallest planet yet found around a star like our sun. The planet is slightly larger than our moon, measuring about one-third the size of Earth. Kepler-37b orbits its host star every 13 days at less than one-third the distance Mercury is to the sun. The estimated surface temperature of this smoldering planet, at more than 800 degrees Fahrenheit (700 degrees Kelvin), would melt the zinc in a penny.

Astronomers don't think the tiny planet has an atmosphere or could support life as we know it, but the moon-size world is almost certainly rocky in composition.

The Kepler-37 planetary system is approximately 210 light-years away in the constellation Lyra.

  • The Los Angeles Times (2/21, Brown, 692K) reports Barclay said scientists are "breaking new ground" with the discovery, who noted that a total of three planets have been found in the system. While none are similar to Earth, Barclay, according to the article, claimed the "discovery is still 'really good news' for the search for habitable worlds...because it demonstrates that the Kepler telescope is sensitive enough to find Earth-sized planets with longer orbits 'in the not-too distant future.'" Caltech's John Johnson, who was not part of the study, praised Kepler for making exoplanet discoveries "blasé" with the what it has found.
  • The Boulder (CO) Daily Camera (2/21, Brennan, 40K) reports on the ties the mission and the discovery has to the region as Barclay said, "This project would not have been possible if not for the exquisite instrument built at Ball." Meanwhile, Alan Gould, a co-investigator for education and public outreach for the Kepler mission, said, "The significance as far as I'm concerned is that when the mission first started it was hoped that we could find planets smaller than Mars, and we thought it might be able to find planets as small as Mercury. ... So, this is momentous in that here is a planet smaller than Mercury, and it is totally due to the incredibly precise light measuring capability of the Kepler instrument."
  • According to the Christian Science Monitor (2/21, Spotts, 47K), in another result from this study, "Kepler's ability to take very precise measurements of the star's own light helped the team develop a highly accurate estimate of the star's size and mass."
  • SPACE (2/21, Howell) notes "Barclay and his team took great care to confirm the existence of planets around Kepler-37."
  • Also covering the story are Bloomberg News (2/21, Lopatto), CBS News (2/21, Harwood) "Space" website, BBC News (2/21, Palmer), Popular Science (2/21, Nosowitz, 1.3M), Wired (2/21, Mann, 798K) "Wired Science" blog, ScienceNOW (2/21, Croswell, 128K), New Scientist (2/21, Aron), Discovery News (2/21, Klotz), another Discovery News (2/21, O'Neill) article, Gizmag (2/21, Szondy), UK's Daily Mirror (2/21, Rankin, 1.32M),PolicyMic (2/21, Marin), Scientific American (2/21, Matson, 483K), China's Xinhua (2/21) news agency, Sen(2/21, Black), Universe Today (2/21, Atkinson), The Escapist (2/21, Bolding), Geekosystem (2/21, Chant), andGizmodo (2/21, Diaz).
  • Blog Coverage. Alex Knapp at Forbes (2/21, 928K) notes, "One other interesting thing about this finding, as Phil Plait notes, is that a portion of the research was crowdfunded. The money came from the Pale Blue Dot Project, which allows people to 'adopt' a Kepler star to support exoplanetary research. The money raised helped to support the astroseismology involved in this research."

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