TOI-1268b: The youngest hot Saturn-mass transiting exoplanet

¹ Astronomical Institute, Czech Academy of Sciences, Fričova 298, 251 65 Ondřejov, Czech Republic
e-mail: jan.subjak@asu.cas.cz
² Astronomical Institute of Charles University, V Holešovičkách 2, 180 00 Prague, Czech Republic
³ ESO, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany
⁴ Department of Astronomy, The University of Texas at Austin, Austin, TX 78712, USA
⁵ Center for Planetary Systems Habitability, The University of Texas at Austin, Austin, TX 78712, USA
⁶ Thueringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
⁷ McDonald Observatory, The University of Texas at Austin, Austin, TX 78712, USA
⁸ Dipartimento di Fisica, Università degli Studi di Torino, via Pietro Giuria 1, 10125 Torino, Italy
⁹ Centre for Astronomy and Astrophysics, Technical University Berlin, 10585 Berlin, Germany
¹⁰ Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstraße 2, 12489 Berlin, Germany
¹¹ Vanderbilt University, Department of Physics & Astronomy, 6301 Stevenson Center Ln., Nashville, TN 37235, USA
¹² Fisk University, Department of Physics, 1000 18th Ave. N., Nashville, TN 37208, USA
¹³ Instituto de Astrofísica de Canarias (IAC), Calle Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
¹⁴ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38205 La Laguna, Tenerife, Spain
¹⁵ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
¹⁶ Rheinisches Institut für Umweltforschung an der Universität zu Köln, Aachener Strasse 209, 50931 Köln, Germany
¹⁷ Department of Theoretical Physics and Astrophysics, Masaryk University, Kotlářská 2, 61137 Brno, Czech Republic
¹⁸ Astronomy Department, University of California, Berkeley, CA 94720, USA
¹⁹ California Institute of Technology, Pasadena, CA 91125, USA
²⁰ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²¹ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
²² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
²³ Leiden Observatory, Leiden University, NL-2333 CA Leiden, The Netherlands
²⁴ NASA Ames Research Center, Moffett Field, CA 94035, USA
²⁵ Department of Space, Earth and Environment, Astronomy and Plasma Physics, Chalmers University of Technology, 412 96 Gothenburg, Sweden
²⁶ Department of Astronomy, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
²⁷ Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²⁸ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²⁹ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
³⁰ NCCR/Planet-S, Universität Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
³¹ Astronomy Department and Van Vleck Observatory, Wesleyan University, Middletown, CT 06459, USA
³² Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
³³ Department of Aeronautics and Astronautics, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA

Received: 10 December 2021
Accepted: 16 February 2022

Abstract

We report the discovery of TOI-1268b, a transiting Saturn-mass planet from the TESS space mission. With an age of less than 1 Gyr, derived from various age indicators, TOI-1268b is the youngest Saturn-mass planet known to date; it contributes to the small sample of well-characterised young planets. It has an orbital period of P = 8.1577080 ± 0.0000044 days, and transits an early K-dwarf star with a mass of M_* = 0.96 ± 0.04 M_⊙, a radius of R_* = 0.92 ± 0.06 R_⊙, an effective temperature of T_eff = 5300 ± 100 K, and a metallicity of 0.36 ± 0.06 dex. By combining TESS photometry with high-resolution spectra acquired with the Tull spectrograph at the McDonald Observatory, and the high-resolution spectrographs at the Tautenburg and Ondřejov Observatories, we measured a planetary mass of M_p = 96.4 ± 8.3 M_⊕ and a radius of R_p = 9.1 ± 0.6 R_⊕. TOI-1268 is an ideal system for studying the role of star-planet tidal interactions for non-inflated Saturn-mass planets. We used system parameters derived in this paper to constrain the planet’s tidal quality factor to the range of 10^4.5–5.3. When compared with the sample of other non-inflated Saturn-mass planets, TOI-1268b is one of the best candidates for transmission spectroscopy studies.