The TESS-Keck Survey. XII. A Dense 1.8 R ⊕ Ultra-short-period Planet Possibly Clinging to a High-mean-molecular-weight Atmosphere after the First Gigayear
Batalha, Natalie M.; Mayo, Andrew W.; Rice, Malena; Kane, Stephen R.; Huber, Daniel; Howard, Andrew W.; Petigura, Erik A.; Behmard, Aida; Chontos, Ashley; Crossfield, Ian J. M.; Dalba, Paul A.; Rubenzahl, Ryan A.; Weiss, Lauren M.; Fetherolf, Tara; Lissauer, Jack J.; Dai, Fei; Angelo, Isabel; Giacalone, Steven; Fulton, Benjamin; Robertson, Paul; Blunt, Sarah; Polanski, Alex S.; Isaacson, Howard; Beard, Corey; Holcomb, Rae; Lubin, Jack; Dressing, Courtney; Brinkman, Casey L.; Hill, Michelle L.; MacDougall, Mason G.; Scarsdale, Nicholas; Tyler, Dakotah; Van Zandt, Judah; Mortier, Annelies; Murphy, Joseph M. Akana; Yee, Samuel W.; Mocnik, Teo; Pidhorodetska, Daria; Turtelboom, Emma V.; Malavolta, Luca; Pedani, Marco; Fiorenzano, Aldo
United States, Australia, Italy, United Kingdom, Spain
Abstract
The extreme environments of ultra-short-period planets (USPs) make excellent laboratories to study how exoplanets obtain, lose, retain, and/or regain gaseous atmospheres. We present the confirmation and characterization of the USP TOI-1347 b, a 1.8 ± 0.1 R ⊕ planet on a 0.85 day orbit that was detected with photometry from the TESS mission. We measured radial velocities of the TOI-1347 system using Keck/HIRES and HARPS-N and found the USP to be unusually massive at 11.1 ± 1.2 M ⊕. The measured mass and radius of TOI-1347 b imply an Earth-like bulk composition. A thin H/He envelope (>0.01% by mass) can be ruled out at high confidence. The system is between 1 and 1.8 Gyr old; therefore, intensive photoevaporation should have concluded. We detected a tentative phase-curve variation (3σ) and a secondary eclipse (2σ) in TESS photometry, which, if confirmed, could indicate the presence of a high-mean-molecular-weight atmosphere. We recommend additional optical and infrared observations to confirm the presence of an atmosphere and investigate its composition.