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TOI-1634 b: An Ultra-short-period Keystone Planet Sitting inside the M-dwarf Radius Valley

2021; Institute of Physics; Volume: 162; Issue: 2 Linguagem: Inglês

10.3847/1538-3881/ac0157

1538-3881

Ryan Cloutier, David Charbonneau, Keivan G. Stassun, F. Murgas, A. Mortier, Bob Massey, Jack J. Lissauer, David W. Latham, Jonathan Irwin, R. D. Haywood, P. Guerra, Éric Girardin, Steven Giacalone, P. Bosch-Cabot, Allyson Bieryla, Joshua N. Winn, C. A. Watson, R. Vanderspek, S. Udry, Motohide Tamura, A. Sozzetti, Avi Shporer, D. Ségransan, Sara Seager, Arjun B. Savel, Dimitar Sasselov, Mark E. Rose, G. Ricker, Ken Rice, Elisa V. Quintana, Samuel N. Quinn, G. Piotto, David F. Phillips, F. Pepe, M. Pedani, H. Parviainen, Ε. Πάλλη, Norio Narita, E. Molinari, G. Micela, Scott McDermott, M. Mayor, Rachel A. Matson, A. F. Martínez Fiorenzano, C. Lovis, Mercedes López‐Morales, Nobuhiko Kusakabe, Eric L. N. Jensen, Jon M. Jenkins, Chelsea X. Huang, Steve B. Howell, A. Harutyunyan, Gábor Fűrész, Akihiko Fukui, Gilbert A. Esquerdo, E. Esparza-Borges, X. Dumusque, Courtney D. Dressing, Luca Di Fabrizio, Karen A. Collins, A. Collier Cameron, Jessie L. Christiansen, M. Cecconi, Lars A. Buchhave, W. Boschin, G. Andreuzzi,

Astrophysics and Star Formation Studies

Studies of close-in planets orbiting M dwarfs have suggested that the M dwarf radius valley may be well-explained by distinct formation timescales between enveloped terrestrials, and rocky planets that form at late times in a gas-depleted environment. This scenario is at odds with the picture that close-in rocky planets form with a primordial gaseous envelope that is subsequently stripped away by some thermally-driven mass loss process. These two physical scenarios make unique predictions of the rocky/enveloped transition's dependence on orbital separation such that studying the compositions of planets within the M dwarf radius valley may be able to establish the dominant physics. Here, we present the discovery of one such keystone planet: the ultra-short period planet TOI-1634 b ($P=0.989$ days, $F=121 F_{\oplus}$, $r_p = 1.790^{+0.080}_{-0.081} R_{\oplus}$) orbiting a nearby M2 dwarf ($K_s=8.7$, $R_s=0.45 R_{\odot}$, $M_s=0.50 M_{\odot}$) and whose size and orbital period sit within the M dwarf radius valley. We confirm the TESS-discovered planet candidate using extensive ground-based follow-up campaigns, including a set of 32 precise radial velocity measurements from HARPS-N. We measure a planetary mass of $4.91^{+0.68}_{-0.70} M_{\oplus}$, which makes TOI-1634 b inconsistent with an Earth-like composition at $5.9\sigma$ and thus requires either an extended gaseous envelope, a large volatile-rich layer, or a rocky portion that is not dominated by iron and silicates to explain its mass and radius. The discovery that the bulk composition of TOI-1634 b is inconsistent with that of the Earth favors the gas-depleted formation mechanism to explain the emergence of the radius valley around M dwarfs with $M_s\lesssim 0.5 M_{\odot}$.