Astronomers Locate First Earth-Mass Planet That Transits Its Host Star

Posted on January 7, 2014

KOI-314c Earth-mass planet

Astronomers have located the first Earth-mass planet that transits its host star. The planet, KOI-314c, is also the lightest planet to have both its mass and physical size measured. The planet has a mass the same as the Earth but it is 60% bigger than Earth in diameter. An artist's conception of the planet is pictured above.

KOI-314c orbits a dim, red dwarf star located about 200 light-years away. It is close to its star and circles it every 23 days. The team of astronomers estimate the planet has a very hot surface temperature of 220 degrees Farenheit.

The international team of astronomers was lead by David Kipping of the Harvard-Smithsonian Center for Astrophysics (CfA). Kipping said in the announcement, "This planet might have the same mass as Earth, but it is certainly not Earth-like. It proves that there is no clear dividing line between rocky worlds like Earth and fluffier planets like water worlds or gas giants."

The astronomers used a technique called transit timing variations (TTV) to weigh the planet. TTV only works when more than one planet orbits the star.

David Nesvorny of the Southwest Research Institute (SwRI) explains. He says, "Rather than looking for a wobbling star, we essentially look for a wobbling planet. Kepler saw two planets transiting in front of the same star over and over again. By measuring the times at which these transits occurred very carefully, we were able to discover that the two planets are locked in an intricate dance of tiny wobbles giving away their masses."

A draft version of a research paper published about the Earth-mass planet can be found here.

Photo: C. Pulliam & D. Aguilar (CfA)