Astronomers using ESA’s CHaracterising ExOPlanet Satellite (CHEOPS) have discovered a fifth planet around the bright, Sun-like star HD 108236.
An artist’s impression of the five-planet system HD 108236. Image credit: Sci-News.com.
HD 108236 is a star of spectral and luminosity type G3V located 211 light-years away in the southern constellation of Centaurus.
Also known as TOI-1233, TIC 260647166, and HIP 60689, the star is 12% smaller than our Sun and 13% less massive.
In 2020, four large planets were discovered around HD 108236 using data from NASA’s Transiting Exoplanet Survey Satellite (TESS).
The innermost planet, HD 108236b, is a hot super-Earth with a radius of 1.6 times that of the Earth.
It has a period of 3.9 days, making it the hottest known planet in the HD 108236 system with an estimated temperature of 826 degrees Celsius (1,519 degrees Fahrenheit).
The three outer planets, HD 108236c, d and e, are sub-Neptunes with radii 2.1, 2.7, and 3.1 Earth radii and periods 6.2, 14.2, and 19.6 days, respectively.
“From the TESS measurements, it follows that the inner planet lies inside the radius gap, while the three larger outer planets are located around the peak comprising planets with a gaseous envelope, hence making this system of particular interest for atmospheric evolution studies,” said Dr. Andrea Bonfanti from the Space Research Institute of the Austrian Academy of Sciences and his colleagues.
In the new study, the astronomers used the high-precision photometry data from the CHEOPS mission to characterize the HD 108236 multi-planet system and the host star.
“We characterized the host star through spectroscopic analysis and derived the radius with the infrared flux method,” they explained.
“We analyzed the available TESS light curves and one CHEOPS transit light curve for each known planet in the system.”
The new CHEOPS data also revealed that there is an additional transiting planet in the system.
Designated HD 108236f, it has a mass about two times that of the Earth and an orbital period of 29.54 days.
“The detection of the fifth planet makes HD 108236 the third system brighter than V = 10 mag to host more than four transiting planets,” the researchers said.
Their paper will be published in the journal Astronomy & Astrophysics.
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A. Bonfanti et al. 2021. CHEOPS observations of the HD 108236 planetary system: A fifth planet, improved ephemerides, and planetary radii. A&A, in press; arXiv: 2101.00663
