A Giant Planet Transiting A 0.2 Solar Mass Host Star

Planet formation models suggest that the formation of giant planets is significantly 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 MP = 0.168 ± 0.022 MJ (53.4 ± 7.1 M⊕) and RP = 0.855 ± 0.022 RJ, and likely 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 at mospheric characterization observations, which will be key for fully interpreting the formation history of this remarkable system and for the study of atmospheric methane chemistry.