We report the discovery of the transiting planet GJ 238 b, with a radius of 0.566±0.014 R⊕ (1.064±0.026 times the radius of Mars) and an orbital period of 1.74 day. The transit signal was detected by the TESS mission and designated TOI-486.01. The star's position close to the Southern ecliptic pole allows for almost continuous observations by TESS when it is observing the Southern sky. The host star is an M2.5 dwarf with V=11.57±0.02 mag, K=7.030±0.023 mag, a distance of 15.2156±0.0030 pc, a mass of 0.4193−0.0098+0.0095 M⊙, a radius of 0.4314−0.0071+0.0075 R⊙, and an effective temperature of 3,485±140 K. We validate the planet candidate by ruling out or rendering highly unlikely each of the false positive scenarios, based on archival data and ground-based follow-up observations. Validation was facilitated by the host star's small size and high proper motion, of 892.633±0.025 mas yr−1.
@article{arxiv.2407.18199,
title = {GJ 238 b: A 0.57 Earth Radius Planet Orbiting an M2.5 Dwarf Star at 15.2 pc},
author = {Evan Tey and Avi Shporer and Zifan Lin and Keivan G. Stassun and Jack J. Lissauer and Coel Hellier and Karen A. Collins and Kevin I. Collins and Geof Wingham and Howard M. Relles and Franco Mallia and Giovanni Isopi and John F. Kielkopf and Dennis M. Conti and Richard P. Schwarz and Aldo Zapparata and Steven Giacalone and Elise Furlan and Zachary D. Hartman and Steve B. Howell and Nicholas J. Scott and Carl Ziegler and Cesar Briceno and Nicholas Law and Andrew W. Mann and David Charbonneau and Zahra Essack and Stephanie Striegel and George R. Ricker and Roland Vanderspek and Sara Seager and Joshua N. Winn and Jon M. Jenkins},
journal= {arXiv preprint arXiv:2407.18199},
year = {2024}
}