binary planet system
Artist's rendition of the Kepler-47 system. Credit: NASA/JPL-Caltech/T. Pyle

A team of astronomers, including University of Hawaiʻi at Mānoa Associate Astronomer Nader Haghighipour, has discovered the first two-planet system orbiting two stars. Their study was published in the journal Science.

Known as Kepler-47 because the data came from the Kepler spacecraft, this planetary system demonstrates that complete planetary systems can exist around a pair of stars.

The system contains the smallest known planet orbiting a pair of binary stars. The radius of the inner planet is only three times that of Earth and orbits the binary stars every 49 days. The radius of the outer planet is 4.6 times that of Earth (about the size of Uranus), and it orbits the binary every 303 days, making it the longest orbital period transiting planet known to date. A planet transits its star when it crosses in front of it as seen from Earth, or in this case, by Kepler.

More important, the outer planet’s orbit and the spectral types of the stars (G and M) place the planet well within the “habitable zone,” the region where a terrestrial planet could have liquid water on its surface. While this planet is most likely a gas-giant planet like Jupiter and not a terrestrial planet like Earth, and is thus not suitable for life, its discovery establishes that circumbinary planets can, and do, exist in habitable zones.

Adapted from a University of Hawaiʻi at Mānoa Institute of Astronomy news release.