An article published in “The Astronomical Journal” reports the confirmation of four exoplanets, one super-Earth and three mini-Neptunes, in the system of the star HD 108236. A team led by Tansu Daylan, postdoc Kavli Institute for Astrophysics and Space Research at MIT, analyzed data collected by NASA’s TESS space telescope to identify those exoplanets. Two high school students also participated in this research as part of the Student Research Mentoring Program (SRMP) at the Center for Astrophysics | Harvard & Smithsonian. An article accepted for publication in the journal “Astronomy & Astrophysics” reports the discovery of another super-Earth in the same system by a team of researchers led by Andrea Bonfanti of the Austrian Academy of Sciences that used ESA’s CHEOPS space telescope.
About 210 light-years from Earth, the star HD 108236 has a mass and size nearly 90% the Sun’s. It might be older than the Sun, but estimates of its age contain a large margin of error. Being among the targets of observations for the TESS space telescope, launched on April 18, 2018, it’s also known as TOI-1233 where the acronym TOI stands for TESS Object of Interest.
Tansu Daylan’s team, which includes the two high school students Kartik Pinglé, aged 16, and Jasmine Wright, aged 18, analyzed observations of the star HD 108236 conducted by the TESS space telescope and discovered four planets. The data indicates that they are a super-Earth with a mass a little more than four times the Earth’s and three mini-Neptunes of various sizes. They’re all very close to their star with years lasting 3.8, 6.2, 14.18, and 19.6 Earth days respectively.
New observations of the HD 108236 system with the TESS space telescope are expected in 2021. Meanwhile, it has already been a target for the CHEOPS space telescope, launched on December 18, 2019, designed to examine exoplanets discovered with other instruments to characterize them. Andrea Bonfanti’s team also discovered another planet in that system thanks to CHEOPS, probably another super-Earth. Its mass is almost four times the Earth’s, but it’s a little larger than the innermost one and therefore with a lower density. It’s the outermost planet discovered so far in the system but, like the other planets, is too close to its star to have conditions similar to those of Earth. The first estimate of its year’s length is just over 29 Earth days, so it could be a super-Mercury.
Even though the planets of HD 108236 are far too close to their star to host Earth-like life forms, it’s always interesting for astronomers to discover a system with multiple planets. It offers new information that will help improve planet formation and evolution models. In this case, hot Neptune planets were found, Neptune-sized gas planets close to their star. They will offer information on the erosion of these planets’ atmosphere by their star. For these reasons, the HD 108236 system will keep on being studied.
It’s the second case in a short time of exoplanets in a planetary system discovered by putting together the data collected by the TESS and CHEOPS space telescopes after the TOI-178 system’s case. The different characteristics of these two instruments led to a synergy that perhaps not even astronomers expected with excellent results.
