tidal dissipation inflates WASP-12b ?

In Nature

Quote :

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

Shu-lin Li1,2,4, N. Miller3, Douglas N. C. Lin1,3 & Jonathan J. Fortney3

Kavli Institute for Astronomy and Astrophysics,
Department of Astronomy, Peking University, Beijing 100871, China
Department of Astronomy and Astrophysics, University of California, Santa Cruz 95064, USA

The class of exotic Jupiter-mass planets that orbit very close to their parent stars were not explicitly expected before their discovery1. The recently discovered2 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 ± 0.09R 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.

Wow. That will be very interesting to see confirmed.

Now at Arxiv:

http://arxiv.org/abs/1002.4608

Press release article plus a very amusing graphic.

http://kiaa.pku.edu.cn/Destiny/Destiny_of_hot_Jupiters.html

i have some questions

Is it normal that gas makes a disc around the star and not a tail behind the planet? Why? It is explained in the paper, but why it does not arrive at HD 209458 b for example?


Why the gas is drawn in front of the planet and not behind? Should not he be evicted by the pressure of light and of wind of the star?

In a Sudarsky's like classification, what should resemble this planet?

Stalker wrote:

Is it normal that gas makes a disc around the star and not a tail behind the planet? Why?

Yes, this is normal. The expelled matter interacts with itself and the planet and looses speed. It's easier to fall toward the star than to oppose the gravitational gradient.

Stalker wrote:

Why the gas is drawn in front of the planet and not behind? Should not he be evicted by the pressure of light and of wind of the star?

Stellar irradiation causes atmospheric escape, leading to an envelope of escaped material around the planet. The star tidally distorts this exosphere into a teardrop shape. With the vertex of the teardrop at the L₁ point. This location becomes a nozzle for which gas to escape toward the star. I suspect hydrogen does not get pushed out of the system by solar wind fast enough for it to make a significant difference in the disk density. Moreover, the material in the disk falls toward the star.

Stalker wrote:

In a Sudarsky's like classification, what should resemble this planet?

Class V.

Regarding the mass loss inwards through L1 instead of being driven outwards by the solar wind, from the supplementary information:

Quote :

The wind’s ram pressure Ṁ_wv_m/4πa² on WASP-12b’s dayside could potentially exceed the planet’s atmospheric thermal pressure and perturb the flow toward the night side but it is inadequate to push the gas to overcome the gravitational potential difference 2GM_*/3a between L₁ and the outer Lagrangian point at L₂.