Follow this link to skip to the main content
NASA Ames Research Center
RSS Send
Home > News



Kepler-20 system: 5 planets including two that are Earth-size
12.20.2011
refer to caption
This chart compares the first Earth-size planets found around a sun-like star to planets in our own solar system, Earth and Venus.NASA's Kepler mission discovered the newfound planets, called Kepler-20e and Kepler-20f. Kepler-20e is slightly smaller than Venus with a radius .87 times that of Earth. Kepler-20f is a bit larger than Earth at 1.03 times the radius of Earth. Venus is very similar in size to Earth, with a radius of .95 times that our planet. The images of Kepler-20e and f are artist conceptions.

Prior to this discovery, the smallest known planet orbiting a sun-like star was Kepler-10b with a radius of 1.42 that of Earth, which translates to 2.9 times the volume.

Both Kepler-20e and Kepler-20f circle in close to their star, called Kepler-20, with orbital periods of 6.1 and 19.6 days, respectively. Astronomers say the two little planets are rocky like Earth but with scorching temperatures.

Image credit: NASA/Ames/JPL-Caltech
Visit also:

NASA's Kepler mission discovered the first Earth-size planets around a star beyond our own. The system is jam-packed with five planets, all circling within a distance roughly equivalent to Mercury's orbit in our solar system.

The two Earth-size planets, which are presumably rocky, are Kepler-20e and Kepler-20f, and the three larger gas planets are Kepler-20b, Kepler-20c and Kepler-20d. The arrangement of the planets from the closest to its star to the farthest is: b, e, c, f and d, with the ordering of the letters reflecting the time at which the planets were initially discovered.

Refer to caption
This is an artist's conception of Kepler-20e, the first planet smaller than the Earth discovered to orbit a star other than the sun. A year on Kepler-20e only lasts 6 days, as it is much closer to its host star than the Earth is to the sun. The temperature at the surface of the planet, around 1400 degrees Fahrenheit, would melt glass—much to hot to support life, as we know it.

Kepler-20e is likely to be entirely rocky and without an atmosphere. The planet is tidally locked, always showing the same side to its host star, as the moon to the Earth, and could have large temperature differences between its permanent night and day sides.

Astronomers think that the planet is likely to be geologically active, due to its own formation process and the strong gravitational interactions with its host star. In this artistic depiction, the planet is represented with active volcanoes on both the night and day sides.

Image credit: NASA/Ames/JPL-Caltech

“The primary goal of the Kepler mission is to find Earth-sized planets in the habitable zone," said Francois Fressin of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., lead author of a new study published in the journal Nature. "This discovery demonstrates for the first time that Earth-size planets exist around other stars, and that we are able to detect them.”

The Kepler-20 system includes three other planets that are larger than Earth but smaller than Neptune. Kepler-20b, the closest planet, Kepler-20c, the third planet, and Kepler-20d, the fifth planet, orbit their star every 3.7, 10.9 and 77.6 days. The host star belongs to the same G-type class as our sun, although it is slightly smaller and cooler. The system has an unexpected arrangement. In our solar system, small, rocky worlds orbit close to the sun and large, gaseous worlds orbit farther out. In comparison, the planets of Kepler-20 are organized in alternating size: large, small, large, small and large.

"The Kepler data are showing us some planetary systems have arrangements of planets very different from that seen in our solar system," said Jack Lissauer, planetary scientist and Kepler science team member at NASA's Ames Research Center in Moffett Field, Calif. "The analysis of Kepler data continue to reveal new insights about the diversity of planets and planetary systems within our galaxy."

"In the cosmic game of hide and seek, finding planets with just the right size and just the right temperature seems only a matter of time," said Natalie Batalha, Kepler deputy science team lead and professor of astronomy and physics at San Jose State University. "We are on the edge of our seats knowing that Kepler's most anticipated discoveries are still to come."

ALT Refer to caption
This is an artist's conception of Kepler-20f, the closest object to the Earth in terms of size ever discovered. With an orbital period of 20 days and a surface temperature of 800 degrees Fahrenheit, it is too hot to host life, as we know it.

Image credit: NASA/Ames/JPL-Caltech

ANIMATION (right-click to download):
Refer to caption
Click on the above image to download .mp4 animation. This artist's animation flies through the Kepler-20 star system, where NASA's Kepler mission discovered the first Earth-size planets around a star beyond our own. The system is jam-packed with five planets, all circling within a distance roughly equivalent to Mercury's orbit in our solar system.

The two Earth-size planets, which are presumably rocky, are Kepler-20e and Kepler-20f, and the three larger gas planets are Kepler-20b, Kepler-20c and Kepler-20d. The arrangement of the planets from the closest to its star to the farthest is: b, e, c, f and d, with the ordering of the letters reflecting the time at which the planets were initially discovered.

This animation begins by showing the farthest planet from the star, Kepler-20d, then flies over to Kepler-20f and moves on successively to closer and closer planets. It then pans out to show all five planets in the miniature solar system.

The Kepler-20 system is unusual in that the sizes of the planets alternate, with the closest in being large, followed by a small planet, and then continuing on with the planets switching back and forth in size. Astronomers are intrigued by this configuration because it completely differs from that of our solar system, where there is a clear separation between the four small, rocky inner planets, and the four giant, gaseous outer planets.

Image credit: NASA/Ames/JPL-Caltech


Audio Recording:

Panelists:

  • Nick Gautier, Kepler project scientist, NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.
  • Francois Fressin, lead author, Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
  • David Charbonneau, professor of astronomy, Harvard University
  • Linda Elkins-Tanton, director of the Carnegie Institution for Science's Department of Terrestrial Magnetism in Washington.

Return to News Archive