About 400 light years away, the planet, known as Kepler-78b, circles a star that is slightly smaller than the sun located in the constellation Cygnus
At the end of October, Scientists for the first time 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.
One light year, is the distance light, moving at 186,282 miles per second (299,792 kilometers per second) travels in a year
Kepler-78b was discovered last year with NASA's now-idled Kepler space telescope, which detected potential planets as they circled in front of their parent stars, blocking a bit of light.
That measurement not only revealed that Kepler-78b was relatively small, with a diameter just 20 percent larger than Earth's, but that it was practically orbiting on the surface of its host star.
