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Published February 2023 | Published
Journal Article Open

TOI-1136 is a Young, Coplanar, Aligned Planetary System in a Pristine Resonant Chain


Convergent disk migration has long been suspected to be responsible for forming planetary systems with a chain of mean-motion resonances (MMRs). Dynamical evolution over time could disrupt the delicate resonant configuration. We present TOI-1136, a 700 ± 150 Myr old G star hosting at least six transiting planets between ∼2 and 5 R_⊕. The orbital period ratios deviate from exact commensurability by only 10⁻⁴, smaller than the ∼10⁻² deviations seen in typical Kepler near-resonant systems. A transit-timing analysis measured the masses of the planets (3–8 M_⊕) and demonstrated that the planets in TOI-1136 are in true resonances with librating resonant angles. Based on a Rossiter–McLaughlin measurement of planet d, the star's rotation appears to be aligned with the planetary orbital planes. The well-aligned planetary system and the lack of a detected binary companion together suggest that TOI-1136's resonant chain formed in an isolated, quiescent disk with no stellar flyby, disk warp, or significant axial asymmetry. With period ratios near 3:2, 2:1, 3:2, 7:5, and 3:2, TOI-1136 is the first known resonant chain involving a second-order MMR (7:5) between two first-order MMRs. The formation of the delicate 7:5 resonance places strong constraints on the system's migration history. Short-scale (starting from ∼0.1 au) Type-I migration with an inner disk edge is most consistent with the formation of TOI-1136. A low disk surface density (Σ_(1 au) ≲ 10³ g cm⁻²; lower than the minimum-mass solar nebula) and the resultant slower migration rate likely facilitated the formation of the 7:5 second-order MMR.

Additional Information

© 2023. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. We thank Doug Lin, Eric Agol, Dan Fabrycky, Sarah Millholland, Jared Siegel, Ji-Wei Xie, Wenrui Xu, Wei Zhu, Shuo Huang, and André Izidoro for insightful comments. We thank Armaan Goyal for computing the Ginni Index for TOI-1136 and the Kepler sample. We thank Cicero Lu for investigating the spectral energy distribution of this system. We acknowledge the use of public TESS data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. J.L-B. acknowledges financial support received from "la Caixa" Foundation (ID 100010434) and from the European Unions Horizon 2020 research and innovation program under the Marie Slodowska-Curie grant agreement No. 847648, with fellowship code LCF/BQ/PI20/11760023. This research has also been partly funded by the Spanish State Research Agency (AEI) Projects No. PID2019-107061GB-C61. J.M.A.M. is supported by the National Science Foundation Graduate Research Fellowship Program under grant No. DGE-1842400. J.M.A.M. acknowledges the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining grant No. 1829740, the Brinson Foundation, and the Moore Foundation; his participation in the program has benefited this work. Based on observations (program ID: A43/TAC11) made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Funding for the Stellar Astrophysics Centre is provided by The Danish National Research Foundation (grant agreement No. DNRF106). Software: Isoclassify (Huber 2017), COMOVE (Tofflemire et al. 2021), lmfit (Newville et al. 2014), Batman (Kreidberg 2015), REBOUND (Rein & Liu 2012), emcee (Foreman-Mackey et al. 2013), JAX (Bradbury et al. 2018).

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August 22, 2023
August 22, 2023