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

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-circle dot, a radius of R-* = 0.92 +/- 0.06 R-circle dot, 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 Ondrejov Observatories, we measured a planetary mass of M-p = 96.4 +/- 8.3 M-circle plus and a radius of R-p = 9.1 +/- 0.6 R-circle plus. 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.

Automated summary

We report the discovery of TOI-1268b, a young Saturn-mass planet, from the TESS space mission. Its orbital period, host star parameters, and planet's mass and radius are measured, making it an ideal candidate for studying young planets and for transmission spectroscopy studies.