  We investigate the hypothesis that ingestion of a terrestrial or super-Earth
planet could cause the anomalously high metal abundances seen in a turn-off
star in the open cluster M67, when compared to other turn-off stars in the same
cluster. We show that the mass in convective envelope of the star is likely
only $3.45\,\times 10^{-3}\,{\rm M}_\odot$, and hence $5.2\,{\rm M}_\oplus$ of
rock is required to obtain the observed 0.128 dex metal enhancement. Rocky
planets dissolve entirely in the convective envelope if they enter it with
sufficiently tangential orbits: we find that the critical condition for
dissolution is that the planet's radial speed must be less than 40% of its
total velocity at the stellar surface; or, equivalently, the impact parameter
must be greater than about 0.9. We model the delivery of rocky planets to the
stellar surface both by planet-planet scattering in a realistic multi-planet
system, and by Lidov-Kozai cycles driven by a more massive planetary or stellar
companion. In both cases almost all planets that are ingested arrive at the
star on grazing orbits and hence will dissolve in the surface convection zone.
We conclude that super-Earth ingestion is a good explanation for the metal
enhancement in M67 Y2235, and that a high-resolution spectroscopic survey of
stellar abundances around the turn-off and main sequence of M67 has the
potential to constrain the frequency of late-time dynamical instability in
planetary systems.
