It's rocky, like Earth, but too hot for life as we know it.
One side of the planet is about 2,700 degrees Fahrenheit because of its proximity to a star.
The planet is called Kepler 10B after the telescope that found it.
Natalie Batalha, an astronomer from San Jose State University is part of the discovery team. Astronomers have found other planets outside our solar system that are closer in mass to earth, but none this small.