Researchers in the MOA group, in cooperation with the groups μFUN, OGLE, and WISE, using gravitational microlensing, discovered an Earth-like planet orbiting a star in a binary system 3,000 light-years from Earth. The planet discovered has a mass approximately twice that of Earth and its orbit radius is about 0.8 astronomical units (AU), similar to the distance between Earth and the Sun

Because the planet’s host star has a low mass, one-tenth that of the Sun, and is, therefore, less luminous, the planet’s surface temperature is -210 degrees C, much colder than that of the Earth. In fact, it’s a little colder than that of Europa, one of Jupiter’s moons. The host star in this binary system has a close companion with a nearly equal mass. The companion star is 15 AU away from the host star, about the distance between the Sun and Saturn. This is the first discovery of a planet in a binary system in which the orbit and mass of the planet are similar to those of Earth. About half of all stars in the universe are to be found in binary systems; however, thus far it’s been difficult to discover planets in binary systems making this field in astronomy poorly explored.

This group’s discovery has clarified the existence of a terrestrial planet orbiting a star in a binary system, and the method which they used enhances the possibility of further investigations into earth-like planets.

(Courtesy of Cheongho Han, Chungbuk National University, Republic of Korea)

(Link) http://resou.osaka-u.ac.jp/en/research/2014/20140704_1