Astronomers have discovered Earth's gassy twin with a mass similar to that of our planet in another solar system 200 light years away.
Article continues below
An international team discovered the first Earth-mass planet that transits, or crosses in front of, its host star. KOI-314c is the lightest planet to have both its mass and physical size measured. Surprisingly, although the planet weighs the same as Earth, it is 60 percent larger in diameter, meaning that it must 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 giants," said David Kipping of the Harvard-Smithsonian Centre for Astrophysics (CfA), lead author of the discovery.
The team gleaned the planet's characteristics using data from NASA's Kepler spacecraft. KOI—314c orbits a dim, red dwarf star located approximately 200 light—years away. It circles its star every 23 days. The team estimates its temperature to be 104 degrees Celsius, too hot for life as we know it. 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.
It 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, researchers said. Conventionally, astronomers measure the mass of an exoplanet by measuring the tiny wobbles of the parent star induced by the planet's gravity. This radial velocity method is extremely difficult for a planet with Earth's mass. The previous record holder for a planet with a measured mass (Kepler-78b) weighed 70 per cent more than Earth.
To weigh KOI-314c, the team relied on a different technique known as transit timing variations (TTV). 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 in the system, KOI-314b, is about the same size as KOI-314c but significantly denser, weighing about 4 times as much as Earth. It orbits the star every 13 days, meaning it is in a 5-to-3 resonance with the outer planet. ■