The third planet discovered in the star system Kepler-47 has been identified by scientists as the largest exoplanet within the circumbinary star system.

A group of researchers led by astronomers from San Diego State University detected the new exoplanet, which they estimate is as big as Neptune or Saturn, using data from NASA's Kepler space telescope.

With three planets and two suns, the circumbinary system Kepler-47 is one of the most interesting star systems ever studied by scientists because it is the only known binary star system with multiple planets.

In fact, the system's newly identified exoplanet dubbed as Kepler-47d orbits between two previously known planets called Kepler-47b and Kepler-47c.

Details Of The New Study

Astronomer Jerome Orosz and his colleagues at the San Diego State University surveyed the new data collected by NASA's Kepler space telescope. The team was able to isolate the dimming caused by the third exoplanet's orbital path across the face of the binary stars.

Orosz said they saw a clue that there might be a third planet in the star system in 2012, but because they only had data of one transit, they were still unsure.

Thanks to the additional transit, they were able to determine the new exoplanet's orbital period. He and his team were also able to uncover more transits that were hidden among the sea of data.

The orbital plane of Kepler-47d has been estimated to become more aligned with that of Earth and the binary suns in its own system, which increases the strength of the exoplanet's transit signal.

Third Planet In Kepler-47 Is Largest Exoplanet

All the planets in Kepler-47 have surprisingly low densities, and neither the suns nor the planets are hot, scientists said. Low density is not unusual for exoplanets that are sizzling hot and are the size of Jupiter, but it is definitely rare for exoplanets that have mild temperatures.

The equilibrium temperature of Kepler-47d is at least 50 o F, while the equilibrium temperature of Kepler-47c is at least 26 o F. The innermost planet, which is the smallest circumbinary planet ever discovered, has an equilibrium temperature of 336 o F.

All of the exoplanets in this circumbinary system enjoy intimate orbits, where the two suns orbit each other every 7.45 days, and the entire system could fit within the orbit of Earth. The system is approximately 3,340 light-years away in the direction of the Cygnus constellation.

Additionally, the fact that Kepler-47d is the largest planet in the entire system came off as a surprise to researchers.

"We certainly didn't expect it to be the largest planet in the system. This was almost shocking," said astronomer William Welsh, one of the coauthors of the study.

Implications Of The Study

Such a discovery is important because it is evidence that binary star systems can host multiple planets. It is also because binary star systems are much more common than solo star systems such as our very own solar system.

Furthermore, the findings of the study build on one of the Kepler space telescope's most interesting discoveries, which is that systems of closely packed, low-density planets are common in the Milky Way galaxy, said Jonathan Fortney, a scientist from University of California, Santa Cruz who was not part of the study.

In the meantime, details of the new study have been published in the Astronomical Journal.

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