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GJ 238 b: A Mars-size planet orbiting an M2.5 dwarf star at 15.2 pc

Presentation #600.07 in the session Planet Detection - Transits.

Published onApr 03, 2024
GJ 238 b: A Mars-size planet orbiting an M2.5 dwarf star at 15.2 pc

The search for small terrestrial planets, the size of Earth and smaller, is now at the forefront of exoplanet research. Their discovery puts the Solar System terrestrial planets in the context of exoplanets. We report the discovery of GJ 238 b, a transiting planet close to Mars radius, at 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 0.42 MSun, a radius of 0.43 RSun, 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 per year.

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