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

February 2023 • 2023AJ....165...33D

Authors • Dai, Fei • Masuda, Kento • Beard, Corey • Robertson, Paul • Goldberg, Max • Batygin, Konstantin • Bouma, Luke • Lissauer, Jack J. • Knudstrup, Emil • Albrecht, Simon • Howard, Andrew W. • Knutson, Heather A. • Petigura, Erik A. • Weiss, Lauren M. • Isaacson, Howard • Kristiansen, Martti Holst • Osborn, Hugh • Wang, Songhu • Wang, Xian-Yu • Behmard, Aida • Greklek-McKeon, Michael • Vissapragada, Shreyas • Batalha, Natalie M. • Brinkman, Casey L. • Chontos, Ashley • Crossfield, Ian • Dressing, Courtney • Fetherolf, Tara • Fulton, Benjamin • Hill, Michelle L. • Huber, Daniel • Kane, Stephen R. • Lubin, Jack • MacDougall, Mason • Mayo, Andrew • Močnik, Teo • Akana Murphy, Joseph M. • Rubenzahl, Ryan A. • Scarsdale, Nicholas • Tyler, Dakotah • Zandt, Judah Van • Polanski, Alex S. • Schwengeler, Hans Martin • Terentev, Ivan A. • Benni, Paul • Bieryla, Allyson • Ciardi, David • Falk, Ben • Furlan, E. • Girardin, Eric • Guerra, Pere • Hesse, Katharine M. • Howell, Steve B. • Lillo-Box, J. • Matthews, Elisabeth C. • Twicken, Joseph D. • Villaseñor, Joel • Latham, David W. • Jenkins, Jon M. • Ricker, George R. • Seager, Sara • Vanderspek, Roland • Winn, Joshua N.

Abstract • 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 (3-8M ) 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 (Σ1 au ≲ 103g 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.

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