Kepler-78b is a planet that shouldn’t exist. This scorching lava world circles its star every eight and a half hours at a distance of less than one million miles — one of the tightest known orbits. According to current theories of planet formation, it couldn’t have formed so close to its star, nor could it have moved there.
“This planet is a complete mystery,” says astronomer David Latham of the Harvard-Smithsonian Center for Astrophysics (CfA). “We don’t know how it formed or how it got to where it is today. What we do know is that it’s not going to last forever.”
“Kepler-78b is going to end up in the star very soon, astronomically speaking,” agrees CfA astronomer Dimitar Sasselov.
Not only is Kepler-78b a mystery world, it is the first known Earth-sized planet with an Earth-like density. Kepler-78b is about 20 percent larger than 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.
Read more: http://www.sciencedaily.com/releases/2013/10/131030142915.htm