Kepler finds smallest exoplanet yet

Posted by Emma Woollacott

Astronomers have found the smallest planet yet outside our solar system, a rocky planet about one and a half times the size of Earth.

Discovered by NASA's Kepler mission, Kepler-10b is denser than Earth, with 4.6 times its volume. This gives it much the same density as an iron dumbell, says NASA.

It was detected by measuring the Doppler Shift in its star's spectrum caused by the tug of the planet.

"All of Kepler's best capabilities have converged to yield the first solid evidence of a rocky planet orbiting a star other than our sun," said Natalie Batalha, Kepler's deputy science team lead.

"The Kepler team made a commitment in 2010 about finding the telltale signatures of small planets in the data, and it's beginning to pay off."

Orbiting once every 0.84 days, Kepler-10b is more than 20 times closer to its star than Mercury is to our sun and is therefore decidedly uninhabitable. Temperatures at the surface are likely to be well over a thousand degrees Centigrade, and any atmosphere would be long gone.

But, says Kepler program scientist Douglas Hudgins, "The discovery of Kepler 10-b is a significant milestone in the search for planets similar to our own. Although this planet is not in the habitable zone, the exciting find showcases the kinds of discoveries made possible by the mission and the promise of many more to come."

It's not the first roughly Earthlike planet to be discovered: that honor goes to Corot-7b, discovered in 2009. Corot-7b has a mass about five times that of Earth, with a similar density.