Conditions on Hot Jupiters

Hot Jupiters are close to their parent star - after all, that's why they're so hot. Their atmospheres are thought to be slowly blown away by the parent star, and they will eventually become chthonian planets.

Are there any other effects on Hot Jupiters because of their proximity to their parent star? Examples I'm looking for include issues with solar flares or coronal mas ejections, or even difficulties relating to the solar wind. I would also be tangentially interested in any effects the parent star would have on moon formation (or lack thereof).

I think we can broadly distinguish two classes of effects here:

• Flares directly affecting the planet
• The by-products of the flare affecting the planet

I can loosely tell you what I know (although my knowledge here is far from being complete)

Direct effects include:

• Magnetic field geometries: Far-away from their host star (>0.05AU) planets usually have isolated dipoles. The solar wind then must penetrate the magnetosphere of a planet to erode its atmosphere. This is however much easier for the wind if due to small distance both star and planet-magnetospheres connect. What this will lead to, is quasi-free flow of a significant portion of the stars total ejected mass towards the planet and huge energy input into the planet's upper atmosphere.

Indirect physics can be:

An active young star can have frequent outbreaks of CMEs, those are accompanied by strong UV / X-ray emission and this will affect the planet:

• Increased photochemistry: This can generate a very active photochemistry in the upper atmospheres. Doubly ionized molecules like $O_2^{++}$ or $N_2^{++}$ can then be produced more efficiently and eject their constituents into space upon dissociation due to high dissociation energies
• UV-X-heating: Additional heat through thermalized high-energy photons can add to the already happening 'natural' atmospheric erosion.

We don't know however, to which extent those effects play a role. I'd add tomorrow some references if you're interested.

There could be signs however of such activity in young stellar systems, as verious combinations or extensions of the above have been proposed to explain the radius anomaly in super-close extrasolar giant planets.

• Thanks. These are just the kinds of things I was looking for. Sep 14, 2014 at 21:18
• Cool. I'll add some refs and perhaps pics tomorrow, cuz I'm too lazy to search for the papers now ;) Sep 14, 2014 at 21:20