An Earth-sized Planet on the Verge of Tidal Disruption

TL;DR

TOI-6255 b is an Earth-sized planet on the verge of tidal disruption, providing insights into planetary deformation, orbital decay, and potential star-planet interactions near the Roche limit.

Contribution

This study reports the discovery and characterization of an Earth-sized planet close to tidal disruption, including mass, size, and orbital parameters, and predicts its future orbital decay.

Findings

Planet's mass: 1.44±0.14 M_⊕

Orbital period: 5.7 hours

Predicted Roche limit approach in 400 Myr

Abstract

TOI-6255~b (GJ 4256) is an Earth-sized planet (1.079$\pm0.065$ $R_\oplus$) with an orbital period of only 5.7 hours. With the newly commissioned Keck Planet Finder (KPF) and CARMENES spectrographs, we determined the planet's mass to be 1.44$\pm$0.14 $M_{\oplus}$. The planet is just outside the Roche limit, with $P_{\rm orb}/P_{\rm Roche}$ = 1.13 $\pm0.10$. The strong tidal force likely deforms the planet into a triaxial ellipsoid with a long axis that is $\sim$10\% longer than the short axis. Assuming a reduced stellar tidal quality factor $Q_\star^\prime \approx10^7$, we predict that tidal orbital decay will cause TOI-6255 to reach the Roche limit in roughly 400 Myr. Such tidal disruptions may produce the possible signatures of planet engulfment that have been on stars with anomalously high refractory elemental abundances compared to its conatal binary companion. TOI-6255 b is also a favorable target for searching for star-planet magnetic interactions, which might cause interior melting and hasten orbital decay. TOI-6255 b is a top target (Emission Spectroscopy Metric of about 24) for phase curve observations with the James Webb Space Telescope.