  The 4.2-day orbit of the newly discovered planet around 51~Pegasi is formally
unstable to tidal dissipation. However, the orbital decay time in this system
is longer than the main-sequence lifetime of the central star. Given our best
current understanding of tidal interactions, a planet of Jupiter's mass around
a solar-like star could have dynamically survived in an orbit with a period as
short as $\sim10\,$hr. Since radial velocities increase with decreasing period,
we would expect to find those planets close to the tidal limit first and,
unless this is a very unusual system, we would expect to find many more. We
also consider the tidal stability of planets around more evolved stars and we
re-examine in particular the question of whether the Earth can dynamically
survive the red-giant phase in the evolution of the Sun.
