Discovey of the closest rocky exoplanet
Astronomers have detected the nearest rocky planet known beyond our solar system, using the HARPS-North ground-based instrument and the NASA Spitzer Space Telescope. The planet, called HD 219134b, is a mere 21 light-years away, within a stone's throw at the scale of the Galaxy. It is a bit larger than Earth, and of similar composition. This planet is also the closest exoplanet, or a planet beyond our solar system, that can be seen "transiting," crossing in front of its star, making it the perfect planetary specimen for future studies. The paper presenting the discovery has been accepted for publication in the journal Astronomy & Astrophysics.
HD 219134b is located in the familiar Cassiopeia constellation near the North Star. While the planet can't be seen directly, even by space telescopes, its star is visible to the naked eye in dark skies next to one leg of Cassiopeia's "W" shape. At 21 light-years away, it is one of the closest known exoplanets. Only 12 confirmed exoplanets are closer to Earth than HD219134b, the closest one, named GJ674b, being 15 light-years away. Still, none of these 12 closer planets transit, so astronomers have no information about their size and composition.