Distant planet sets speed record by orbiting its star every 8.5 hours

U.S. scientists say an exoplanet around a distant star has one of the shortest "years" ever observed, whizzing around its parent star in a little over 8 hours. The Earth-sized exoplanet named Kepler 78b, located 700 light years away, has one of the shortest orbital periods ever detected, researchers at the Massachusetts Institute of Technology reported Monday. The rapid orbiting is the result of the planet's extreme proximity to its star -- its orbital radius is only about three times the radius of the star -- and researchers say they estimate its surface temperatures may be as high as 5,000 degrees Fahrenheit. The top layer of the planet is likely completely melted, creating a massive, constantly roiling ocean of lava, they said. Measurements of Kepler 78b have determined the planet is about 40 times closer to its star than Mercury is to our sun, they said. For the planet to maintain its extremely tight orbit around its star it would need to be incredibly dense -- it's likely made almost entirely of iron -- otherwise, the researchers said, the immense tidal forces from the nearby star would rip it to pieces. "Just the fact that it's able to survive there implies that it's very dense," MIT physics Professor Josh Winn said. "Whether nature actually makes planets that are dense enough to survive even closer in, that's an open question, and would be even more amazing." Winn and his colleagues have been looking for Earth-sized planets with very short orbital periods. "We've gotten used to planets having orbits of a few days," he said. "But we wondered, what about a few hours? Is that even possible? And sure enough, there are some out there."