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Kepler's Smallest Habitable Zone Planets
04.18.2013

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We're a step closer to knowing if our galaxy is home to a multitude of planets like Earth or if we are a rarity. The three habitable zone super-Earth-size planets are in two systems containing a total of seven newly discovered planets:

  • Star Kepler-62 is not Sun-like: just 2/3 the size of the Sun, cooler, older, and only 1/5 as bright.
    • Planet Kepler-62f, 40% larger than Earth, the smallest known habitable zone exoplanet, orbits every 267 days.
    • Planet Kepler-62e, about 60% larger than Earth, orbits every 122 days in the the habitable zone's inner edge.
    • Kepler-62b, Kepler-62c and Kepler-62d, orbit every 5, 12, and 18 days, respectively, making them very hot and inhospitable for life as we know it. Two are larger than Earth and one is about the size of Mars.
Kepler-62 diagram
This diagram compares the planets of the inner solar system to the five planets of Kepler-62, a star just two thirds the size of the sun and only one fifth as bright. Two of the planets, Kepler-62f and Kepler-62e, lie in the star's habitable zone. The planets shown are artist's depictions. Credit: NASA/Ames/JPL-Caltech




  • Star Kepler-69 is a sun-like star (G-type, 93% the size of the Sun, 80% as luminous, about 2,700 light-years from Earth).
    • Planet Kepler-69c is 70% larger than Earth, the smallest yet found in the habitable zone of a sun-like star. It orbits in 242 days, resembling the orbit of Venus.
    • Planet Kepler-69b is just over twice the size of Earth and, orbiting every 13 days, is toasty hot, not even close to the habitable zone.
Kepler-69 system diagram
Kepler-69 System Diagram compared the planets of the inner solar system. Kepler-69c is the smallest planet yet found in the habitable zone of a G-type sun-like star. Its 242-day orbit resembles that of our neighboring planet Venus. Planet Kepler-69b orbits every 13 days, nowhere near the habitable zone. The Kepler-69 planets shown are artist's concepts. Credit: NASA/Ames/JPL-Caltech.




"Finding a planet in the habitable zone around a star like our sun is a significant milestone toward finding truly Earth-like planets," said Thomas Barclay, Kepler scientist at the Bay Area Environmental Research Institute in Sonoma, Calif., and lead author of the Kepler-69 system discovery published in the Astrophysical Journal.

See Full NASA Press Release.

Kepler-62 Morning Star
Kepler-62 Morning Star. This artist's concept depicts in the foreground planet Kepler-62f, a super-Earth-size planet in the habitable zone of its star which is seen peeking out from behind the right edge of the planet. The small shining object farther to the right is Kepler-62e which orbits on the inner edge of the habitable zone of the star. If someday in the distant future we landed on the right spot on Kepler-62f, just before "sunrise" we'd be treated to a lovely view of Kepler-62e as a "morning star" much like Venus often appears for us on Earth. Credit: NASA/Ames/JPL-Caltech.


Kepler62f
Artist's concept of Kepler-62f, a super-Earth-size planet in the habitable zone of a star smaller and cooler than the Sun. Though the size of Kepler-62f is known (40% larger than Earth), its mass and composition are not. Credit: NASA/Ames/JPL-Caltech.


Kepler-62e
Artist's concept depicts Kepler-62e, a super-Earth-size planet orbiting it's host star's habitable zone. We know that Kepler-62e is roughly 60 percent larger than Earth but we do not know if Kepler-62e is a waterworld or if it has a solid surface. Credit: NASA/Ames/JPL-Caltech.


Animation of Kepler-62
Kepler-62 animation


Kepler69c
Super-Venus. Artist's concept of planet Kepler-69c, a super-Earth-size planet (70% larger than Earth). It is the smallest yet found orbiting in the habitable zone of a sun-like star. Its orbit of 242 days resembles that of our neighboring planet Venus. Credit: NASA/Ames/JPL-Caltech.


"The Kepler spacecraft has certainly turned out to be a rock star of science," said John Grunsfeld, associate administrator of the Science Mission Directorate at NASA Headquarters in Washington.
"The discovery of these rocky planets in the habitable zone brings us a bit closer to finding a place like home. It is only a matter of time before we know if the galaxy is home to a multitude of planets like Earth, or if we are a rarity."

Relative sizes of Kepler habitable zone planets
Relative sizes of Kepler habitable zone planets discovered as of 2013 April 18.
Left to right: Kepler-22b, Kepler-69c, Kepler-62e, Kepler-62f, and Earth (except for Earth, these are artists' renditions). Credit: NASA/Ames/JPL-Caltech.
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Source of images below: The San Diego Union-Tribune

UT San Diego graphic of Kepler-62e and -62f. Size comparison of Kepler-62 planets. Explaining the different parts of a light curve.

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