  When main-sequence stars expand into red giants, they are expected to engulf
close-in planets. Until now, the absence of planets with short orbital periods
around post-expansion, core-helium-burning red giants has been interpreted as
evidence that short-period planets around Sun-like stars do not survive the
giant expansion phase of their host stars. Here we present the discovery that
the giant planet 8 Ursae Minoris b orbits a core-helium-burning red giant. At a
distance of only 0.5 au from its host star, the planet would have been engulfed
by its host star, which is predicted by standard single-star evolution to have
previously expanded to a radius of 0.7 au. Given the brief lifetime of
helium-burning giants, the nearly circular orbit of the planet is challenging
to reconcile with scenarios in which the planet survives by having a distant
orbit initially. Instead, the planet may have avoided engulfment through a
stellar merger that either altered the evolution of the host star or produced 8
Ursae Minoris b as a second-generation planet. This system shows that
core-helium-burning red giants can harbour close planets and provides evidence
for the role of non-canonical stellar evolution in the extended survival of
late-stage exoplanetary systems.
