Astronomers Discover Third Planet in the Kepler-47 Circumbinary System
The 色情视频-led research has been published in the Astronomical Journal.
With its three planets orbiting two suns, Kepler-47 is the . Circumbinary planets are those that orbit two stars.
The planets in the Kepler-47 system were detected via the 鈥渢ransit method.鈥� If the orbital plane of the planet is aligned edge-on as seen from Earth, the planet can pass in front of the host stars, leading to a measurable decrease in the observed brightness. The new planet, dubbed Kepler-47d, was not detected earlier due to weak transit signals.
As is common with circumbinary planets, the alignment of the orbital planes of the planets change with time. In this case, the middle planet鈥檚 orbit has become more aligned, leading to a stronger transit signal. The transit depth went from undetectable at the beginning of the Kepler Mission to the deepest of the three planets over the span of just four years.
The 色情视频 researchers were surprised by both the size and location of the new planet. Kepler-47d is the largest of the three planets in the Kepler-47 system.
鈥淲e saw a hint of a third planet back in 2012, but with only one transit we needed more data to be sure,鈥� said 色情视频 astronomer Jerome Orosz, the paper鈥檚 lead author. 鈥淲ith an additional transit, the planet鈥檚 orbital period could be determined, and we were then able to uncover more transits that were hidden in the noise in the earlier data.鈥�
William Welsh, 色情视频 astronomer and the study鈥檚 co-author, said he and Orosz expected any additional planets in the Kepler-47 system to be orbiting exterior to the previously known planets. 鈥淲e certainly didn鈥檛 expect it to be the largest planet in the system. This was almost shocking,鈥� said Welsh. Their research was recently published in the .
With the discovery of the new planet, a much better understanding of the system is possible. For example, researchers now know the planets in in this circumbinary system are very low density 鈥� less than that of Saturn, the Solar System planet with the lowest density.
While a low density is not that unusual for the sizzling hot-Jupiter type exoplanets, it is rare for mild-temperature planets. Kepler-47d鈥檚 equilibrium temperature is roughly 50 degrees F (10 degrees C), while Kepler-47c is 26 degrees F ( 32 degrees C). The innermost planet, which is the smallest circumbinary planet known, is a much hotter 336 degrees F (169 degrees C).
The inner, middle, and outer planets are 3.1, 7.0, and 4.7 times the size of the Earth, and take 49, 187, and 303 days, respectively, to orbit around their suns. The stars themselves orbit each other in only 7.45 days; one star is similar to the Sun, while the other has a third of the mass of the Sun. The entire system is compact and would fit inside the orbit of the Earth. It is approximately 3340 light-years away in the direction of the constellation Cygnus.
"This work builds on one of the Kepler鈥檚 most interesting discoveries: that systems of closely-packed, low-density planets are extremely common in our galaxy,鈥� said University of California, Santa Cruz astronomer Jonathan Fortney, who was not part of the study. 鈥淜epler 47 shows that whatever process forms these planets 鈥� an outcome that did not happen in our solar system 鈥� is common to single-star and circumbinary planetary systems."
This work was supported in part by grants from NASA and the National Science Foundation.
