WASP-18b is also a strong contender in the least-habitable-
planet-yet-detected competition. It has a mass roughly ten times
Jupiter’s and skims 2.6 stellar radii above the surface of the
parent star. The orbital period is a mere 22 hours 36 minutes. A
year in less than a day. To the offhand glance, even the simple
presence of the planet seems puzzling. It’s so close to its
parent star that tidal orbital decay should haul it in for
destruction on a timescale that’s alarmingly short in comparison
to the ~1 billion year age of the parent star. Either WASP-18b
has been found on the very cusp of its dénouement (which seems
unlikely) or tidal dissipation in the parent star is much lower
than in a star like the Sun. Darin Ragozzine pointed me to to a
recent article by Barker and Ogilvie that indicates that WASP-18
may indeed be very poor at dissipating tidal energy. It’s an
F-type star, somewhat more massive than the sun, with a
negligible convective envelope, and no good recourse to turning
tidal waves into heat. I