Description
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+/-0.040R_e_, a mass of M_b_=1.21+/-0.42M_e_, and an orbital period of P_b_=2.6162745+/-0.0000030d. The resulting density of rho_b_=4.4+/-1.6g/cm^3^ is compatible with the Earth's mean density of about 5.5g/cm^3^. Due to the apparent brightness of the host star (J=8.7mag) 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+/-0.035d, which is likely unrelated to the stellar rotation period, P_rot_=122+/-13d, which we determined from archival HATNet and ASAS-SN photometry combined with newly obtained TJO data.
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