A low-eccentricity migration pathway for a 13-h-period Earth analogue in a four-planet system

Summary, in English

It is commonly accepted that exoplanets with orbital periods shorter than one day, also known as ultra-short-period (USP) planets, formed further out within their natal protoplanetary disks before migrating to their current-day orbits via dynamical interactions. One of the most accepted theories suggests a violent scenario involving high-eccentricity migration followed by tidal circularization. Here we present the discovery of a four-planet system orbiting the bright (V = 10.5) K6 dwarf star TOI-500. The innermost planet is a transiting, Earth-sized USP planet with an orbital period of ~13 hours, a mass of 1.42 ± 0.18 M⊕, a radius of $$1.16{6}_{-0.058}^{+0.061} \,R_{\oplus}$$and a mean density of $$4.8{9}_{-0.88}^{+1.03}\,{{{\rm{g}}}}\,{{{{\rm{cm}}}}}^{-3}$$. Via Doppler spectroscopy, we discovered that the system hosts 3 outer planets on nearly circular orbits with periods of 6.6, 26.2 and 61.3 days and minimum masses of 5.03 ± 0.41 M⊕, 33.12 ± 0.88 M⊕ and $$15.0{5}_{-1.11}^{+1.12}\,M_{\oplus}$$, respectively. The presence of both a USP planet and a low-mass object on a 6.6-day orbit indicates that the architecture of this system can be explained via a scenario in which the planets started on low-eccentricity orbits then moved inwards through a quasi-static secular migration. Our numerical simulations show that this migration channel can bring TOI-500 b to its current location in 2 Gyr, starting from an initial orbit of 0.02 au. TOI-500 is the first four-planet system known to host a USP Earth analogue whose current architecture can be explained via a non-violent migration scenario.

• Author: Luisa Maria Serrano; Davide Gandolfi; Alexander J. Mustill; Oscar Barragán; Judith Korth; Fei Dai; Seth Redfield; Malcolm Fridlund; Kristine W. F. Lam; Matías R. Díaz; Sascha Grziwa; Karen A. Collins; John H. Livingston; William D. Cochran; Coel Hellier; Salvatore E. Bellomo; Trifon Trifonov; European Southern Observatory Chile; Javier Alarcon; Jon M. Jenkins; David W. Latham; George Ricker; Sara Seager; Roland Vanderspeck; Joshua N. Winn; Simon Albrecht; Kevin I. Collins; Szilárd Csizmadia; Massachusetts Institute Technology; Hans J. Deeg; Massimiliano Esposito; Michael Fausnaugh; Iskra Georgieva; Elisa Goffo; Eike Guenther; Artie P. Hatzes; Steve B. Howell; Eric L. N. Jensen; Rafael Luque; Andrew W. Mann; Felipe Murgas; Hannah L. M. Osborne; Enric Palle; Carina M. Persson; Pam Rowden; Alexander Rudat; Alexis M. S. Smith; Joseph D. Twicken; Vincent Van Eylen; Carl Ziegler
• Department/s: Lund Observatory - Has been reorganised
• Publishing year: 2022
• Language: English
• Pages: 736-750
• Publication/Series: Nature Astronomy
• Volume: 6
• Issue: 6
• Links: https://arxiv.org/abs/2204.13573; http://dx.doi.org/10.1038/s41550-022-01641-y
• Document type: Journal article
• Publisher: Nature Publishing Group
• Topic: Astronomy, Astrophysics and Cosmology
• Status: Published
• Project: Consolidating CHEOPS and preparing for PLATO: Exoplanet studies in the 2020s
• ISBN/ISSN/Other: ISSN: 2397-3366