The results are in – our galaxy harbors at least one hundred billion planets, many of them Earth-sized meaning, small planets like our own are extremely abundant in the universe. On Monday, scientists announced that NASA’s Kepler space telescope has discovered another 461 potential new planets, most of which are the size of Earth or a few times larger. The announcement brings Kepler’s planetary count to 2,740 new exoplanet candidates (planets that orbit stars other than our own), 105 of which have been confirmed, an increase of 43% since Kepler’s catalog was published a year ago. Of the 2,740 objects, 299 are in dual-planet systems, 112 are in triplets, 44 are part of four-planet systems, 11 systems have five planets and one system has six planets. The new targets include KOI-172.02, a planet candidate that’s about 1.5 times bigger than Earth and circles its sunlike parent star in a 242-day orbit. At that distance, liquid water, believed to be necessary for life, could exist on the potential planet’s surface.
The goal of the Kepler mission, which began in 2009, is to determine how many stars in the Milky Way galaxy have an Earth-sized planet orbiting in so-called habitable zones, where water, thought to be necessary for life, can exist on its surface. The Kepler telescope works by tracking slight decreases in the amount of light coming from 160,000 target stars caused by a planet or planets passing by, or transiting, relative to the telescope’s point of view. When an orbiting planet passes in front of the star, Kepler records the small, periodic dip in the star’s brightness. After Kepler discovers a probable planet, ground-based telescopes are used to confirm the results.
A rigorous statistical analysis by Francois Fressin of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, shows that almost all sunlike stars have planetary systems orbiting them and that at least one in six has an Earth-sized planet.