The international collaborative research team "ESPRINT", in which researchers from the Tokyo Institute of Technology, the University of Tokyo, and the Astrobiology Center of the National Institute of Natural Sciences participate, is the second phase of the "Kepler Satellite," a spacecraft that searches for earth-type exoplanets. By combining the observation K2 data and the follow-up observations from the ground, we discovered the giant planet "K2-2b" that revolves in the immediate vicinity of the "quasi-giant star", contrary to conventional expectations.
A "subgiant" is a celestial body in which a star like the sun is aged and swollen.It has been known that there are giant planets around subgiants by searching for exoplanets so far, but few giant planets revolving in the immediate vicinity of subgiants have been discovered.
The main star "K2-39" of the giant planet "K2-39b" discovered this time is a subgiant that is about four times as large as the Sun, and the orbital period of "K4-2b" is about 39 days. The orbit of "K4.6-2b" is only 39 times the diameter of the parent star from "K2-39".Previous predictions are that at such a close orbital distance, the giant planets in the immediate vicinity of the quasi-giant will be destroyed over time by the tidal forces of the parent star (the same force as the moon's ebb and flow of the Earth's ocean). It has been thought that it would end up, but it is believed that the "K1.7-2b" discovered this time is a planet that was fortunately found before it was destroyed by tidal forces.
Studying planets that revolve around old stars will help us understand what happens to the planets around them when they die, and what will happen to the planets of our solar system when the Sun becomes a giant billions of years from now. It is said that it will also lead to understanding.A paper on this discovery will be published in the "Astronomical Journal".
