An international team of astronomers has investigated a planetary system consisting of three alien worlds orbiting the star TOI-396. The study, published Nov. 22 on the pre-print server arXiv, provides the first mass measurements for these three planets, shedding more light on the properties of the whole system.
Located some 103 light years away, TOI-396, also known as HR 858 A, is a bright star of spectral type F6 V, about 26% larger and 20% more massive than the sun. The star, which is estimated to be two billion years old, has an effective temperature of 6,354 K and is part of a binary system—its companion is a faint M dwarf designated HR 858 B.
In 2019, three exoplanets orbiting TOI-396 were detected using NASA’s Transiting Exoplanet Survey Satellite (TESS) and they received designations TOI-396 b, TOI-396 c and TOI-396 d. All the extrasolar worlds turned out to be about two times larger than the Earth and were found to be relatively close to the host—within 0.1 AU from it. The orbital periods of these planets, starting from the innermost, were measured to be 3.6, 6.0 and 11.2 days.
Now, a group of astronomers led by Andrea Bonfanti of the Austrian Academy of Sciences in Graz, Austria, has carried out radial velocity observations of TOI-396 with the High Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph and analyzed photometric data from NASA’s Transiting Exoplanet Survey Satellite (TESS). This allowed them to get more insights into the properties of the system.
“To measure the masses of the three planets, refine their radii, and investigate whether planets b and c are in MMR [mean motion resonance], we carried out HARPS radial velocity observations of TOI-396 and
