Kepler Mission Finds "Smallest" Planet

In a line-up of planets, Kepler-37b doesn't size up to the likes of Earth or even Mercury, but that scientists could detect it at all marks a big step

By Jonathan Lloyd
|  Thursday, Feb 21, 2013  |  Updated 7:19 AM EDT
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Kepler-37b in a lineup with some relative giants in space. Image credit: NASA/Ames/JPL-Caltech

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Scientists on the lookout for habitable planets outside Earth's solar system found a small wonder with a notable distinction -- Kepler-37b is the smallest planet yet discovered that orbits a star similar to our sun.

The planet's discovery was announced Wednesday by scientists who are part of NASA's Kepler mission. It is located near what researchers consider the "habitable zone" -- a system in which water might exist on planets.

It probably does not have an atmosphere that can support life and the 800-degree Fahrenheit surface temperature would be too hot, but Kepler-37b is still a significant find because it suggests the universe is packed with tiny planet candidates.

And, in the haystack of space, Kepler-37b is the needle.

"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," said Thomas Barclay, Kepler scientist at the Bay Area Environmental Research Institute in Sonoma, Calif. "This discovery shows close-in planets can be smaller, as well as much larger, than planets orbiting our sun."

Since Pluto was re-categorized from planet to dwarf planet, Mercury has become the poster-planet for tiny planets. Kepler-37b -- located about 210 light-years from Earth in the constellation Lyra -- is only slightly larger than the moon.

"The fact we've discovered tiny Kepler-37b suggests such little planets are common, and more planetary wonders await as we continue to gather and analyze additional data," said Jack Lissauer, a planetary scientist at NASA's Ames Research Center at Moffett Field.

The potential for detecting planets such as Kepler-37b has increased as technology allowed researchers to find and measure planets smaller than Earth.

The first planets discovered that orbited a sun-like star outside our solar system, called exoplanets, were relative giants. Kepler, launched in 2009 on a hunt for Earth-like planets, provided scientists with a sizeable techological leap.

The space telescope -- Southern California's Jet Propulsion Laboratory managed Kepler mission development -- measures the size of an object when it passes in front of a star. The percentage of light blocked from the telescope's vantage point helps scientists determine the size of the planet.

But to do that, scientists have to determine the size of the star. Using a process called asteroseismology, scientists studied sound waves created by the boiling motion under the star's surface.

The waves create oscillations detected by Kepler -- small stars have high tones, largers ones produce lower tones in the same way different size bells create different tones. The Kepler-37 star's radius is just three-quarters of the sun, so it produces high-frequency oscillations that make it "the smallest bell in the asteroseismology steeple," according to researchers.

The mission's finding were published Wednesday in the journal "Nature."

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