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My understanding is that gas and ice giants form outside the "snow line" of their protoplanetary disk, then sometimes through gravitational interactions they are able to migrate into the inner star system.

In this situation, if the giant planet had moons, what would they be like?

  • Would the planet be able to bring initial moons with it? Or would they be lost?
  • If they are kept, are they likely to retain an icy composition due to forming outside the snowline?
  • If not, can it form or capture new moons post-migration?
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    $\begingroup$ @RobJeffries I am referring to any giant planet that has migrated within the snow line. Jupiter orbits at 5.2AU, while the sun's primordial snow line is estimated to be at ~2.75AU. Are you suggesting that Jupiter came inside this line at some point and then migrated back out? $\endgroup$ – Arkenstein XII Dec 3 '18 at 19:28
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    $\begingroup$ Yes! That is the current thinking - see Grand Tack Hypothesis. en.wikipedia.org/wiki/Grand_tack_hypothesis You also need to be clear whether you are looking for theory or evidence. Other than Jupiter there is little of the latter. $\endgroup$ – ProfRob Dec 3 '18 at 20:04
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    $\begingroup$ Given the icy nature of Jupiter's moons, they must have mostly assembled before any migration inside the snowline. So yes, they must have been dragged in and then dragged out (at least those that survived). If the grand tack happened of course. $\endgroup$ – ProfRob Dec 3 '18 at 20:44
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    $\begingroup$ Have a look at astrobites.org/2015/06/09/… $\endgroup$ – ProfRob Dec 3 '18 at 20:50
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    $\begingroup$ @ArkensteinXII If you calculate the Hill Sphere and the stable part of it being 1/3 to 1/2 the Hill Radius, Jupiter's outermost Galilean Moon Calisto at it's current orbit would remain stable all the way to an orbit slightly inside Venus, so all 4 are pretty stable inside Jupiter's gravity well even during it's suspected migration. Hot Jupiters that get much closer to their suns, however, probably do lose a fair share of their formation moons. $\endgroup$ – userLTK Dec 4 '18 at 0:40

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