  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.
