Discovery and mass measurement of the hot, transiting, Earth-sized planet GJ 3929 b

Abstract

We report the discovery of GJ 3929 b, a hot Earth-sized planet orbiting the nearby M3.5 V dwarf star, GJ 3929 (G 180--18, TOI-2013). Joint modelling of photometric observations from TESS sectors 24 and 25 together with 73 spectroscopic observations from CARMENES and follow-up transit observations from SAINT-EX, LCOGT, and OSN yields a planet radius of $R_b=1.150+/-0.040$ R${}_{earth}$, a mass of $M_b=1.21+/-0.42$ M${}_{earth}$, and an orbital period of $P_b=2.6162745+/-0.0000030$ d. The resulting density of ${\rho }_b=4.4+/-1.6$ g/cm${}^{-3}$ is compatible with the Earth's mean density of about 5.5 g/cm${}^{-3}$. Due to the apparent brightness of the host star (J=8.7 mag) and its small size, GJ 3929 b is a promising target for atmospheric characterisation with the JWST. Additionally, the radial velocity data show evidence for another planet candidate with $P_{[c]}=14.303+/-0.035$ d, which is likely unrelated to the stellar rotation period, $P_{rot}=122+/-13$ d, which we determined from archival HATNet and ASAS-SN photometry combined with newly obtained TJO data.

24 pages; accepted for publication in A&A

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