TESS Hunt for Young and Maturing Exoplanets (THYME). VI. An 11 Myr Giant Planet Transiting a Very-low-mass Star in Lower Centaurus Crux
Owen, James E.; Vanderburg, Andrew; Lester, Kathryn V.; Triaud, Amaury H. M. J.; Latham, David W.; Quinn, Samuel N.; Tang, Shih-Yun; Schlieder, Joshua E.; Howell, Steve B.; Johns-Krull, Christopher M.; Collins, Karen A.; Wohler, Bill; Ricker, George R.; Vanderspek, Roland; Seager, Sara; Winn, Joshua N.; Jenkins, Jon M.; Rizzuto, Aaron C.; Kraus, Adam L.; Guillot, Tristan; Abe, Lyu; Suarez, Olga; Shporer, Avi; Collins, Kevin I.; Barber, Madyson G.; Mann, Andrew W.; Johnson, Marshall C.; Jensen, Eric L. N.; Gan, Tianjun; Prato, L.; Mamajek, Eric E.; Schwarz, Richard P.; Mace, Gregory N.; Furlan, Elise; McLean, Brian; Gnilka, Crystal L.; Kerr, Ronan; Newton, Elisabeth R.; Tofflemire, Benjamin M.; Wood, Mackenna L.; Thao, Pa Chia; Schmidt, Stephen P.; Guerrero, Natalia M.; Mekarnia, Djamel; Bush, Jonathan L.; Fields, Matthew J.; Llama, Joe; Milburn, Reilly P.; Kamler, Jacob; Stahl, Asa G.; Owens, Dylan A.
United States, United Kingdom, China, France
Abstract
Mature super-Earths and sub-Neptunes are predicted to be ≃ Jovian radius when younger than 10 Myr. Thus, we expect to find 5-15 R ⊕ planets around young stars even if their older counterparts harbor none. We report the discovery and validation of TOI 1227b, a 0.85 ± 0.05 R J (9.5 R ⊕) planet transiting a very-low-mass star (0.170 ± 0.015 M ⊙) every 27.4 days. TOI 1227's kinematics and strong lithium absorption confirm that it is a member of a previously discovered subgroup in the Lower Centaurus Crux OB association, which we designate the Musca group. We derive an age of 11 ± 2 Myr for Musca, based on lithium, rotation, and the color-magnitude diagram of Musca members. The TESS data and ground-based follow-up show a deep (2.5%) transit. We use multiwavelength transit observations and radial velocities from the IGRINS spectrograph to validate the signal as planetary in nature, and we obtain an upper limit on the planet mass of ≃0.5 M J. Because such large planets are exceptionally rare around mature low-mass stars, we suggest that TOI 1227b is still contracting and will eventually turn into one of the more common <5 R ⊕ planets.