Kepler Spots Tiniest Trio of Exoplanets

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Astronomers have announced the smallest planets yet discovered outside of our solar system, closely orbiting a dim red dwarf star 130 light-years away.

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The three exoplanets, called KOI-961.01, .02 and .03, are all rocky worlds considerably smaller than Earth and orbit their red star much too closely to be within a habitable zone. Still, the discovery proves that compact planetary systems can exist around these common types of stars… and they can be detected.

The discovery was made by a team of astronomers from California Institute of Technology in Pasadena, using data from NASA's Kepler mission.

The smallest of the exoplanets, KOI-961.03, is 0.57 times the radius of Earth — about the size of Mars. The next larger, KOI-961.02, is 0.73 times Earth's radius, and KOI-961.01 is just slightly larger at 0.78 Earth radii.

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All three worlds are much too hot for liquid water to exist on their surfaces with temperatures ranging from 350 to 836 degrees Fahrenheit (176 to 447 degrees Celsius). They all orbit their home star very quickly, taking less than two days to complete a full "year".

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The M-type red dwarf star these miniature planets orbit, KOI-961, is a sixth the size of our sun and much cooler. In fact, it's only 70 percent larger than Jupiter… and the similarity of the KOI-961 system to the Jovian family hasn't been missed by astronomers.

"The really amazing thing about this system is that the closest size comparison is to Jupiter and its moons," said John Johnson, the principal investigator of the research from NASA's Exoplanet Science Institute at Caltech.

Another correlation noted by researchers is the similarity between KOI-961 and Barnard's star, another M-type red dwarf located much closer to Earth — a mere six light-years away.

In followup observations by the Keck Observatory atop Mauna Kea, Hawaii, the light from both stars were analyzed. Data collected by the Keck I telescope's High Resolution Echelle Spectrometer (HIRES) instrument shows KOI-961 and Barnard's star to be almost identical.

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If small, rocky planets have been discovered around a random, unnamed red dwarf like KOI-961, could there also be Earth-sized planets orbiting Barnard's star in our own galactic backyard? It's been often speculated, but this discovery makes the case that it could soon be proven.

Read more on the NASA news release.

Image credit: NASA/JPL-Caltech