  High-eccentricity tidal migration is a possible way for giant planets to be
emplaced in short-period orbits. If it commonly operates, one would expect to
catch proto-Hot Jupiters on highly elliptical orbits that are undergoing
high-eccentricity tidal migration. As of yet, few such systems have been
discovered. Here, we introduce TOI-3362b (TIC-464300749b), an 18.1-day, 5
$M_{\rm Jup}$ planet orbiting a main-sequence F-type star that is likely
undergoing high-eccentricity tidal migration. The orbital eccentricity is
0.815$^{+0.023}_{-0.032}$. With a semi-major axis of 0.153$^{+0.002}_{-0.003}$
au, the planet's orbit is expected to shrink to a final orbital radius of
0.051$^{+0.008}_{-0.006}$ au after complete tidal circularization. Several
mechanisms could explain the extreme value of the planet's eccentricity, such
as planet-planet scattering and secular interactions. Such hypotheses can be
tested with follow-up observations of the system, e.g., measuring the stellar
obliquity and searching for companions in the system with precise, long-term
radial velocity observations. The variation in the planet's equilibrium
temperature as it orbits the host star and the tidal heating at periapse make
this planet an intriguing target for atmospheric modeling and observation.
Because the planet's orbital period of 18.1 days is near the limit of TESS's
period sensitivity, even a few such discoveries suggest that proto-Hot Jupiters
may be quite common.
