Posted: Thu, Oct 31, 2013, 2:06 PM ET (1806 GMT)
Astronomers announced Wednesday this discovery of an extrasolar planet similar in size and density to the Earth, but closely orbiting its star. Kepler-78b, detected in data from NASA's Kepler spacecraft and later studied by two teams of astronomers, has a diameter about 1.2 times that of the Earth and has a mass twice that of the Earth. That means the planet has a density similar to the Earth, and thus is likely a combination of rock and iron. However, Kepler-78b orbits very close to its star, completing an orbit in just eight and a half hours. Astronomers said they couldn't explain how the planet formed or how it got to its current orbit, but estimated that the star's gravity would break it up in about three billion years.

Related Links:

•  Nature News article
•  New York Times article
•  BBC article
•  Sky & Telescope article
•  Harvard-Smithsonian Center for Astrophysics press release