An Earth-sized Planet on the Verge of Tidal Disruption

TOI-6255 b (GJ 4256) is an Earth-sized planet (1.079±0.065 R⊕) with an orbital period of only 5.7 hours. With the newly commissioned Keck Planet Finder (KPF) and CARMENES spectrograph, we measured the mass of the planet 1.44±0.14 M⊕. The planet seems to be dangerously close to the Roche limit (Porb/PRoche = 1.13 ±0.10). The strong tidal force likely deforms the planet into a triaxial ellipsoid with the long axis being ∼10% longer than the short axis. Assuming a stellar tidal quality factor Q′ ⋆ ≈ 107, we predict that TOI-6255 will reach the Roche Limit in roughly 400 Myr. The eventual tidal disruption may produce the previously suspected planet engulfment signatures: anomalously high refractory elemental abundances in some stellar photospheres. TOI-6255 b is also a top candidate for any star-planet magnetic interaction which may further contribute to orbital decay and interior melting. TOI-6255 b is a top target (Emission Spectroscopy Metric of about 24) for phase curve observations with the James Webb Space Telescope.