Doomed Earth-sized planet a big mystery but a star is in its future

Exoplanet Kepler-78B is almost like Earth, except 2,000 degrees hotter

A newly discovered Earth-like exoplanet is likely covered in lava and really shouldn't exist - and it won't in its current form very much longer astronomers say.

Known as Kepler-78B, the planet is a mystery to astronomers who say its tight orbit around its star - it circles the star every eight and a half hours at a distance of less than one million miles - combined with its intense heat will likely end in a burst of energy.

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"Kepler-78b is going to end up in the star very soon, astronomically speaking," said Harvard-Smithsonian Center for Astrophysics (CfA) astronomer Dimitar Sasselov.

But there's more: According to current theories of planet formation, it couldn't have formed so close to its star, nor could it have moved there., astronomers said.

"It couldn't have formed in place because you can't form a planet inside a star. It couldn't have formed further out and migrated inward, because it would have migrated all the way into the star. This planet is an enigma," explains Sasselov.

Kepler-78b is 400 light years from Earth and is what Sasselov and other astronomers say is a new class of planets that orbit their stars with periods of less than 12 hours. They're also small, about the size of Earth. Kepler-78b is the first planet in the new class to have its mass measured.

Kepler-78b is about 20% larger than the Earth, with a diameter of 9,200 miles, and weighs almost twice as much. As a result it has a density similar to Earth's, which suggests an Earth-like composition of iron and rock, the astronomer stated

"It's Earth-like in the sense that it's about the same size and mass, but of course it's extremely unlike the Earth in that it's at least 2,000 degrees hotter," said Josh Winn, an associate professor of physics at MIT and a member of the Kavli Institute for Astrophysics and Space Research.

Regardless of how it formed, Kepler-78b is a doomed world. Gravitational tides will draw it even closer to its star. Eventually it will move so close that the star's gravity will rip the world apart. Theorists predict that Kepler-78b will vanish within three billion years, the astronomers said.

Two independent research teams then used ground-based telescopes to confirm and characterize Kepler-78b. One team led by Andrew Howard from the University of Hawaii in Honolulu, made follow-up observations using the W. M. Keck Observatory atop Mauna Kea in Hawaii. More information on their research can be found here. The other team led by Francesco Pepe from the University of Geneva, Switzerland, did their ground-base work at the Roque de los Muchachos Observatory on La Palma in the Canary Islands. More information on their research can be found here.

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