Can someone send me pointers to work (either theoretical or simulations) showing (in)stability of satellite orbits around tidally locked exoplanets? I want to know firstly if satellite orbits can survive the inward migration and secondly if once the planet becomes tidally locked if that has any implications for the orbits of its satellites - do they too become tidally locked? How do the tidal interactions from the star impact their orbits? In particular, I'm interested in what happens to orbits of earth-sized moons around gas giants that are in the HZ.


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There is an effect of orbits often talked about with Phobos, moon of Mars, called Tidal Deceleration. Basically, if an object is orbiting quicker than the object around it is orbiting, then it will end up falling into the planet eventually. Any moon that could orbit the planet would have to be orbiting it faster than the orbit of the sun. Therefor, it must be in a state of Tidal Deceleration, which would lend that moon to eventually falling into the planet, or something else.

It might work for a while, but basically it wouldn't work long term.

There does seem to exist another possibility, namely that the planet and moon would be tidally locked to each other, and not the star around which they orbit. This requires similar massed planets, within a factor of maybe 10 or so, but it could in fact happen. Things would have to be just right, however, or this would not work. (Some of this taken from the Bad Astronomy forms)

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    $\begingroup$ Re all that conjecture about earth-sized moons around Jupiters in HZ of cooler stars: so now we have to be careful to only apply it to Jupiters that are not locked (b/c for locked ones, the Earth will spiral into its planet) $\endgroup$
    – Kamal Ali
    Feb 20, 2012 at 5:38
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    $\begingroup$ @KamalAli: Well, they could spiral out of orbit. There also exists a third possibility, but I'd need to do the math. Hmmm. It seems to be a really interesting idea that hasn't been well researched actually... $\endgroup$ Feb 20, 2012 at 13:28

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