Smallest Planet Ever Found By Kepler Scientists
February 20, 2013

Kepler Scientists Discover Smallest Known Planet

Lee Rannals for - Your Universe Online

Another new planetary system has been discovered by Kepler scientists, and this one happens to be home to the smallest planet ever discovered, circling around a star that is strikingly similar to our Sun.

The Kepler-37 system sits about 210 light-years from Earth in the constellation Lyra. Only slightly larger than our moon, smaller than Mercury, and about a third the size of Earth, one of its planets is the smallest ever identified by astronomers. Dubbed Kepler-37b, this mini-planet was found along with two other exoplanets by NASA's Kepler mission, which hunts for Earth-like planets in the so-called "habitable zone" — the region around a star within which it is theoretically possible for a planet to maintain liquid water on its surface.

NASA says that although Kepler 37 system has a star quite similar to our own, it is actually very different than our own Solar System. Kepler-37b does not have an atmosphere, and is unable to support life. Another of the exoplanets, Kepler-37c, is slightly smaller than Venus, or about three-quarters the size of Earth, while Kepler-37d is about twice the size of Earth.

"Even Kepler can only detect such a tiny world around the brightest stars it observes," explained Jack Lissauer, a planetary scientist at NASA's Ames Research Center in Moffett Field, California. "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."

The mini planetary system's star is slightly cooler and a little smaller than our own Sun. Scientists say that all three planets orbit the star at a distance closer than that between Mercury and the Sun. The estimated surface temperature on Kepler-37b is more than 800 degrees Fahrenheit, which is hot enough to melt the metal zinc.

"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, a Kepler scientist at the Bay Area Environmental Research Institute in Sonoma, California and lead author of the new study published in the journal Nature. "This discovery shows close-in planets can be smaller, as well as much larger, than planets orbiting our sun."

Kepler simultaneously measures the brightness of more than 150,000 stars every 30 minutes, looking for "dips" in the intensity of the starlight to spot planets. When a planet passes in front of its star from Kepler's point of view, it helps reveal the transiting planet's size relative to the star.

Scientists also examined sound waves generated by the boiling motion beneath the surface of Kepler 37´s star and probed its interior structure just as geologists use seismic waves generated by earthquakes to probe the interior structure of Earth. As sound waves travel into the star and bring information back to the surface, the waves cause oscillations that Kepler can detect as a flicker in the star's brightness.

Last month, Kepler scientists announced that they had discovered 461 new planet candidates, four of which orbited their respective star´s habitable zone. The new data increased the number of stars discovered that have more than one planet candidate from 365 to 467, not including findings since the first week of January.

“The large number of multi-candidate systems being found by Kepler implies that a substantial fraction of exoplanets reside in flat multi-planet systems,” said Lissauer. “This is consistent with what we know about our own planetary neighborhood.”