A transiting giant planet in orbit around a 0.2-solar-mass host star

Planet formation models indicate that the formation of giant planets is substantially harder around low-mass stars due to the scaling of protoplanetary disc masses with stellar mass. The discovery of giant planets orbiting such low-mass stars thus imposes strong constraints on giant planet formation processes. Here we report the discovery of a transiting giant planet orbiting a 0.207 ± 0.011 M_⊙ star. The planet, TOI-6894 b, has a mass and radius of M_P = 0.168 ± 0.022 M_J (53.4 ± 7.1 M_⊕) and R_P = 0.855 ± 0.022 R_J and probably includes 12 ± 2 M_⊕ of metals. The discovery of TOI-6894 b highlights the need for a better understanding of giant planet formation mechanisms and the protoplanetary disc environments in which they occur. The extremely deep transits (17% depth) make TOI-6894 b one of the most accessible exoplanetary giants for atmospheric characterization observations, which will be key for fully interpreting the formation history of this notable system and for the study of atmospheric methane chemistry.