Tiny Kepler-37b is the smallest exoplanet ever discovered

NASA/Ames/JPL-Caltech
Kepler-37b compared to Earth, the Moon, Mars, Mercury, and various exoplanets.

NASA launched its Kepler space telescope in 2009, and since then, it's discovered a healthy number of exoplanets. This latest discovery is one for the record books, in that it's the smallest planet ever discovered that does not orbit our own sun.

Tiny Kepler-37b is about a third the size of Earth and only slightly larger than the Moon. And since it's smaller than Mercury, if it were in our solar system, it would easily be the smallest planet. Kepler-37b orbits a star about 210 light years away, and this distance makes Kepler-37b's discovery all the more impressive.

Kepler-37b sits very close to its host star; it completes an orbit in only 13 days, and according to NASA, it sits at "less than one-third the distance Mercury is to the sun." And it's toasty: NASA researchers say the planet's surface temperature is over 800 degrees Fahrenheit (700 Kelvin). This puts it at roughly the same temperature as the planet Mercury. According to NASA, Kepler-37b's star is slightly cooler and smaller than the Sun, although it's in the same class as our nearest star.

Scientists think it's a rocky planet and that it lacks an atmosphere. And needless to say, given how close it is to its sun, chances are basically nonexistent that Kepler-37b harbors any life.

NASA/Ames/JPL-Caltech
An artist's conception of Kepler-37b. NASA scientists believe it's a hot, rocky planet that sits very close to its sun.

NASA's come a long way when it comes to finding exoplanets, due in part to the Kepler space telescope. At first, astronomers were only able to locate gas giant exoplanets—think planets like Jupiter and Saturn—so with that in mind, Kepler-37b's discovery is quite an accomplishment. It was also a serious challenge. According to NASA, the Kepler telescope can only detect such tiny planets under certain circumstances.

"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," researcher Thomas Barclay said in a release. "This discovery shows close-in planets can be smaller, as well as much larger, than planets orbiting our sun."

Head on over to NASA's website to learn more about this discovery and the Kepler mission.

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