CAPE CANAVERAL, Florida, Nov 4: For the first time, scientists have found a planet beyond the solar system that not only is the same size as Earth, but has the same proportions of iron and rock, a key step in an ongoing quest to find potentially habitable sister worlds. The planet, known as Kepler-78b, circles a star that is slightly smaller than the sun located in the constellation Cygnus, about 400 light years away. (agencies)