Exoplanet Gassy Earth
January 7, 2014

New Exoplanet Has Mass Like Earth, But Much Gassier

John P. Millis, PhD for redOrbit.com - Your Universe Online

The holy grail of planet hunting is to find the first Earth-like world. While candidates have been found, there has yet to be confirmation about their particular characteristics. However, a new discovery, made possible by an international team of astronomers, has located the first confirmed Earth-mass planet occulting -- that is, passing in front of -- its host star.

Even though the tiny world has the same mass as our planet, the diameter is 60 percent greater. Scientists infer from this that the composition of this new discovery, called KOI-314c, must be dominated by a thick gaseous atmosphere.

"This planet might have the same mass as Earth, but it is certainly not Earth-like," according to David Kipping of the Harvard-Smithsonian Center for Astrophysics (CfA), and lead author of the discovery. "It proves that there is no clear dividing line between rocky worlds like Earth and fluffier planets like water worlds or gas giants."

Even if the planet had been rocky, and therefore also Earth-sized, the proliferation of life on the surface would have been impossible. This is because it has an extremely tight orbit, circling its star every 23 days with surface temperature that likely reach 220 degrees Fahrenheit.

Because of the small mass of KOI-314c, traditional methods of measuring the mass were not sufficient. Most worlds found so far are studied by measuring the 'wobbles' of the parent star due to the gravitational influence of the planet. However, once the mass starts to approach that of Earth, the wobbles are small enough that measurements are unreliable, even with our current technology.

Instead, astronomers actually looked for two planets that were transiting in front of the host star at the same time. They could then look for how the transit times were varying due to the gravitational pull of the planets on each other, instead of their influence on the star.

"Rather than looking for a wobbling star, we essentially look for a wobbling planet," explains co-author David Nesvorny of the Southwest Research Institute (SwRI). "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."

Doing the measurements this way also revealed the mass of the other world, known as KOI-314b. While similarly sized, this planet, which has an even tighter orbital period of 13 days, is much denser, weighing in at some 4 Earth-masses.

This is still a relatively new method for exoplanet discovery and analysis, having only been first successfully conducted in 2010. And, interestingly, its development is not necessarily intended to find Earth-like worlds but rather an even more challenging endeavor: finding exomoons.

"When we noticed this planet showed transit timing variations, the signature was clearly due to the other planet in the system and not a moon. At first we were disappointed it wasn't a moon but then we soon realized it was an extraordinary measurement," says Kipping.

The results of this study were presented this week at the 223rd meeting of the American Astronomical Society in Washington, DC.