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

TL;DR

The discovery of a giant planet orbiting a very low-mass star challenges existing planet formation models and provides a unique opportunity for atmospheric studies to understand such systems.

Contribution

This paper reports the first confirmed transiting giant planet around a 0.2-solar-mass star, providing new insights into planet formation around low-mass stars.

Findings

Giant planet orbiting a 0.2-solar-mass star discovered

Planet has a deep transit of 17%, ideal for atmospheric studies

Planet likely contains about 12 Earth masses of metals

Abstract

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 $0.207 \pm 0.011 M_{\odot}$ star. The planet, TOI-6894 b, has a mass and radius of $M_P = 0.168 \pm 0.022 M_J (53.4 \pm 7.1 M_{\oplus})$ and $R_P = 0.855 \pm 0.022 R_J$, and likely includes $12 \pm 2 M_{\oplus}$ 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 characterisation observations, which will be key for fully interpreting the formation history of this remarkable system and for the study of atmospheric methane chemistry.