"Kepler 78b, a planet some 400 light-years away, is like hell on earth. Astronomers described it on Wednesday as the first Earth-size planet that seems to be made of the same mixture of rock and iron as Earth, and that orbits a star similar to our sun. At that close proximity, the surface of Kepler 78b is infernally hot: 3,500 to 5,000 degrees Fahrenheit, or ... “Exoplanets are just surprising us with their diversity,” said Dimitar D. Sasselov, a professor of astronomy at Harvard and a member of Dr. Pepe’s team, using the name for planets outside our solar...