TOI-7166 b: A Habitable Zone mini-Neptune planet around a nearby low-mass star

We present the discovery and validation of TOI-7166 b, a 2.01 ± 0.05 R⊕ planet orbiting a nearby low-mass star. We validated the planet by combining TESS and multi-color high-precision photometric observations from ground-based telescopes, together with spectroscopic data, high-contrast imaging, archival images, and statistical arguments. The host star is an M4-type dwarf at a distance of ∼35 pc from the Sun. It has a mass and a radius of M⋆ = 0.190 ± 0.004 M⊙ and R⋆ = 0.222 ± 0.005 R⊙, respectively. TOI-7166 b has an orbital period of 12.9 days, which places it close to the inner edge of the Habitable Zone of its host star, receiving an insolation flux of Sp = 1.07 ± 0.08 S⊕ and an equilibrium temperature of Teq = 249 ± 5 K (assuming a null Bond albedo). The brightness of the host star makes TOI-7166 a suitable target for radial velocity follow-up to measure the planetary mass and bulk density. Moreover, the physical parameters of the system including the infrared brightness (Kmag = 10.6) of the star and the planet-to-star radius ratio (0.0823 ± 0.0012) make TOI-7166 b an exquisite target for transmission spectroscopic observations with the JWST, to constrain the exoplanet atmospheric compositions.