A new class of planet

摘要

Although more than 700 extrasolar planets have been detected, none was known to orbit more than one star until the recent discovery1 of a circumbinary planet, which orbits a pair of stars. This concept was previously confined to theory — and to science fiction, for example the planet Tatooine in Star Wars. On page 475 of this issue, Welsh et al.2 describe the discovery of two more such planets and provide insight into their frequency of occurrence. The previously discovered planet~1 and the new ones, each of which orbits its own system of two stars, were found using NASA's Kepler space telescope.