Free Astronomy Magazine

5 EXOPLANETS MAY-JUNE 2014 away A stronomers have achieved another historic result in the long journey taking them toward finding an ex- trasolar planet with characteristics very sim- ilar to those of Earth. That breakthrough step consists in the confirmation of the ex- istence of an Earth-sized planet located in the habitable zone of its star. The main stages leading up to this extra- ordinary milestone had been, since the ‘90s: the discovery of the first planets around stars other than the Sun; the dis- covery of giant planets in the habitable zones of these stars; the discovery of super-Earths both inside and outside the habitable zones; the discovery of Earth- sized planets and even smaller outside the habitable zones; and now the discovery of a potential new Earth. It took more than 20 years to complete the journey that led us from believing that our planetary sys- tem was perhaps unique, to the awareness that in our galaxy alone there may be mil- lions of Earth-like planets. To date, thanks mainly to the Kepler space telescope, astro- nomers have identified over 3,800 candi- date planets, of which around 1,800 have already been confirmed. Among these there is Kepler-186f, the planet that repre- sents the last step before the discovery of an ever increasingly possible “Earth-2”. I n the background, a fantasy view of Kepler- 186 system, with, in the foreground, the Earth-sized planet Kepler-186f. In the video above, an animated reconstruction of that distant planetary system, with the orbits of the four inner planets and an artist’s impres- sion of what Kepler-186f may look like. [NASA Ames / SETI Institute / JPL-Caltech]