Astronomers, led by Dr David Kipping of the Harvard-Smithsonian Center for Astrophysics, have discovered two new extrasolar planets circling a dim, red dwarf star about 200 light-years away from our planet.
This is an artist’s impression of KOI-314c, the lightest planet to have both its mass and physical size measured. KOI-314c interacts gravitationally with another planet, KOI-314b, shown in the background, causing transit timing variations that allow astronomers to measure the masses of both exoplanets. Image credit: C. Pulliam / D. Aguilar / Harvard-Smithsonian Center for Astrophysics.
One of the planets, dubbed KOI-314c, weighs the same as Earth, but around 60 percent larger in diameter.
KOI-314c circles its star every 23 days and has an estimated surface temperature of about 220 degrees Fahrenheit (105 degrees Celsius) – too hot for life as we know it.
According to data from NASA’s Kepler spacecraft, the planet may have a very thick, gaseous atmosphere.
“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 giant,” said Dr Kipping, the lead author of the paper accepted for publication in the Astrophysical Journal (full paper in .pdf / arXiv.org version).
KOI-314c is only 30 percent denser than water. This suggests that the planet is enveloped by a significant atmosphere of hydrogen and helium hundreds of miles thick. The planet might have begun life as a mini-Neptune and lost some of its atmospheric gases over time, boiled off by the intense radiation of its star.
To weigh KOI-314c, the astronomers relied on a technique known as transit timing variations. This method can only be used when more than one planet orbits a star. The two planets tug on each other, slightly changing the times that they transit their star.
The second planet, named KOI-314b, is about the same size as KOI-314c but significantly denser, weighing about 4 times as much as Earth.
KOI-314b orbits the star every 13 days, meaning it is in a 5-to-3 resonance with the outer planet.
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Kipping et al. 2014. The Hunt for Exomoons with Kepler (HEK): IV. A Search for Moons around Eight M-Dwarfs. ApJ, accepted for publication; arXiv: 1401.1210
