TOI-1136 is a Young, Coplanar, Aligned Planetary System in a Pristine Resonant Chain
Fei Dai, K. Masuda, Corey Beard, Paul Robertson, Max Goldberg, Konstantin Batygin, Luke G. Bouma, Jack J. Lissauer, Emil Knudstrup, Simon Albrecht, Andrew W. Howard, Heather A. Knutson, Erik A. Petigura, Lauren M. Weiss, Howard Isaacson, Martti H. Kristiansen, H. P. Osborn, Songhu Wang, Xian-Yu Wang, Aida Behmard, Michael Greklek-McKeon, Shreyas Vissapragada, Natalie M. Batalha, Casey L. Brinkman, Ashley Chontos, Ian J. M. Crossfield, Courtney D. Dressing, Tara Fetherolf, Benjamin J. Fulton, Michelle L. Hill, Daniel Huber, Stephen R. Kane, Jack Lubin, Mason G. MacDougall, Andrew W. Mayo, Teo Močnik, Joseph M. Akana Murphy, Ryan A. Rubenzahl, Nicholas Scarsdale, Dakotah Tyler, Judah Van Zandt, Alex S. Polanski, Hans Martin Schwengeler, Ivan A. Terentev, Paul Benni, Allyson Bieryla, David R. Ciardi, Ben Falk, Elise Furlan, Éric Girardin, P. Guerra, Katharine Hesse, Steve B. Howell, J. Lillo-Box, Elisabeth C. Matthews, Joseph D. Twicken, J. Villaseñor, David W. Latham, Jon M. Jenkins, G. Ricker, Sara Seager, R. Vanderspek, Joshua N. Winn
Abstract
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 (3–8 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 ≲ 10 3 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.