April 16 (UPI) – Astronomers have identified a third exoplanet that orbits the binary star system Kepler-47. With three planets and two suns, Kepler-47 is the only known binary star system with multiple planets.
The proof that binary star systems can hold multiple planets is significant because binary stars are much more common than single stars like the sun.
The new discovery was published this week in the Astronomical Journal.
Scientists previously observed the transits of two planets that revolved around the star duo in Kepler-47, but the third planet's transit signal was weak, making it difficult to detect.
When the researchers examined new data collected by NASA's Kepler space telescope, they were able to isolate the attenuation caused by the orbital path of the third exoplanet through the face of binary stars.
"We saw an indication of a third planet in 2012, but with just one transit we needed more data to be sure," study lead author Jerome Orosz, an astronomer at San Diego State University, said in a news release. "With an additional transit, it was possible to determine the orbital period of the planet, and then we could discover more transits hidden in the noise in the previous data".
Astronomers estimate that the orbital plane of the newly discovered third planet, Kepler-47d, became more aligned with the Earth and its two suns, increasing the strength of its transit signal.
Surprisingly, the new traffic data suggests that the third exoplanet, which orbits the two suns between the other two exoplanets, is the largest of the three, roughly between the sizes of Neptune and Saturn.
All the planets in the Kepler-47 system have surprisingly low densities, and neither the suns nor the planets are particularly hot. All members of the Kepler-47 system enjoy intimate orbits. The two suns orbit each other every 7.45 days, and the entire system could fit within Earth's orbit.