GJ 238 b: A 0.57 Earth Radius Planet Orbiting an M2.5 Dwarf Star at 15.2 pc

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 days. 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 3485 ± 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.

我们报告了凌日行星GJ 238 b的发现，它的半径为0.566 ± 0.014 R⊕（是火星半径的1.064 ± 0.026倍），轨道周期为1.74天。凌日信号由凌日系外行星巡天卫星（TESS）任务探测到，并被命名为TOI - 486.01。该恒星靠近南黄极的位置使得TESS在观测南天时几乎可以进行连续观测。主恒星是一颗M2.5型矮星，视星等V = 11.57 ± 0.02等，K星等 = 7.030 ± 0.023等，距离为15.2156 ± 0.0030秒差距，质量为0.4193−0.0098+0.0095 M☉，半径为0.4314−0.0071+0.0075 R☉，有效温度为3485 ± 140 K。我们通过基于档案数据和地面后续观测排除或使每种假阳性情况极不可能发生，从而验证了这颗行星候选体。主恒星的小尺寸以及892.633 ± 0.025毫角秒/年的高自行促进了验证过程。