WASP-12b as a prolate, inflated and disrupting planet from tidal dissipation

A misshapen hot Jupiter The recently discovered 'hot Jupiter' extrasolar planet WASP-12b is orbiting at a mean distance of only 3.1 stellar radii from its host star, with an orbital period of only 26 hours. Its radius, about 1.8 times that of Jupiter, is unexpectedly large compared to most gas giants of similar mass and orbital period. A new analysis of WASP-12b's properties suggests that the energy sustaining its inflated size comes from tidal forces that cause the atmosphere to escape the planet's gravitational pull and flow towards the host star. As well as losing mass, the planet's shape is distorted into an ellipse by these extreme forces. WASP-12b is a planet of 1.4 Jupiter masses that orbits at a mean distance of only 3.1 stellar radii from its star; its orbital period is 1.1 days, and its radius (1.79 times that of Jupiter) is unexpectedly large. An analysis of its properties now reveals that the planet is losing mass to its host star at a rate of ∼10 −7 Jupiter masses per year, and that dissipation of the star's tidal perturbation in the planet's convective envelope provides the energy source for its large volume. The class of exotic Jupiter-mass planets that orbit very close to their parent stars were not explicitly expected before their discovery 1 . The recently discovered 2 transiting planet WASP-12b has a mass M = 1.4 ± 0.1 Jupiter masses ( M J ), a mean orbital distance of only 3.1 stellar radii (meaning it is subject to intense tidal forces), and a period of 1.1 days. Its radius 1.79 ± 0.09 R J is unexpectedly large and its orbital eccentricity 0.049 ± 0.015 is even more surprising because such close orbits are usually quickly circularized. Here we report an analysis of its properties, which reveals that the planet is losing mass to its host star at a rate of about 10 -7 M J per year. The planet’s surface is distorted by the star’s gravity and the light curve produced by its prolate shape will differ by about ten per cent from that of a spherical planet. We conclude that dissipation of the star’s tidal perturbation in the planet’s convective envelope provides the energy source for its large volume. We predict up to 10 mJy CO band-head (2.292 μm) emission from a tenuous disk around the host star, made up of tidally stripped planetary gas. It may also contain a detectable resonant super-Earth, as a hypothetical perturber that continually stirs up WASP-12b’s eccentricity.