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Artist illustration of Kepler-78b. Credit: Cristina Sanchis Ojeda Artist illustration of Kepler-78b. Credit: Cristina Sanchis Ojeda

Lava world sees in new year every 8.5 hours

Sen— Astronomers have detected a lava world which orbits its star every 8.5 hours - one of the shortest orbital periods ever detected.

The Earth-sized planet, designated Kepler-78b, is 700 light years away and was found by researchers at MIT using data captured by NASA's Kepler space telescope.

The exoplanet orbits its star so closely -- about 40 times closer to its star than Mercury is to the Sun -- that its surface temperature is estimated to be more than 5,000 degrees Fahrenheit. Its surface is likely to be completely melted, coated with an ocean of lava. The fireball's temperature excludes the prospect of it being habitable. 

“You’d have to really stretch your imagination to imagine living on a lava world. We certainly wouldn’t survive there,” explained Josh Winn, an associate professor of physics at MIT. 

Scientists hope to be able to measure the planet's gravitational influence on its star in order to measure the mass of Kepler-78b, which would make it the first Earth-size planet outside our Solar System whose mass is known.

The researchers studying the data on Kepler-78b were also able to detect light emitted by the planet, possibly a combination of radiation from its boiling surface and light reflected by the lava and atmospheric vapor. 

Physics graduate Roberto Sanchis-Ojeda, one of the MIT team, recalled: “I was just looking by eye, and all of a sudden I see this extra drop of light right when it was expected, and it was really beautiful. I thought, we’re actually seeing the light from the planet. It was a really exciting moment.” 

Whilst a year on Kepler-78b is a rapid 8.5 hours, the researchers together with another group of astronomers found an exoplanet with an even shorter year. The exoplanet, designated KOI 1843.03, has an orbital period of just 4.25 hours. With such a tight orbit around its star the planet would have to be very dense -- made almost entirely of iron -- or it would be ripped apart by the star's tidal forces. The study, which is a separate paper to the Kepler-78b research, is published in Astrophysical Journal Letters

Although Kepler-78b is considered uninhabitable, a planet with a similar orbit could be habitable around a brown dwarf - a cold, dim star which has failed to ignite. The MIT researchers are now looking for such exoplanets. 

"If you’re around one of those brown dwarfs, then you can get as close in as just a few days,” explained Winn. “It would still be habitable, at the right temperature.” 

Although Kepler has recently retired from planet hunting due to a mechanical failure, scientists are still wading through the vast amounts of data captured by the telescope during its operative years. 

The MIT research on Kepler-78b is published in The Astrophysical Journal

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