<p>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. </p>

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

<ul>
<li>Would the planet be able to bring initial moons with it? Or would they be lost?</li>
<li>If they are kept, are they likely to retain an icy composition due to forming outside the snowline?</li>
<li>If not, can it form or capture new moons post-migration?</li>
</ul>

CC BY-SA 4.0
2018-12-03T07:39:16.733Z
This is supposed to have happened to Jupiter, so there's your answer
ProfRob
CC BY-SA 4.0
2018-12-03T07:55:09.747Z
Or are you referring to "hot Jupiters"?
ProfRob
CC BY-SA 4.0
2018-12-03T19:28:54.627Z
@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?
Arkenstein XII
CC BY-SA 4.0
2018-12-03T20:04:21.903Z
Yes! That is the current thinking - see Grand Tack Hypothesis. https://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.
ProfRob
CC BY-SA 4.0
2018-12-03T20:28:32.747Z
@RobJeffries Fascinating! That would suggest that the Jovian moons came with Jupiter all the way in, and all the way back out. I think that answers my question pretty succinctly. I realise that we have no observational data beyond our own back yard, I was just curious whether there had been any modelling that suggested whether moons would be kicked out of their orbits or not.
Arkenstein XII
CC BY-SA 4.0
2018-12-03T20:44:12.977Z
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.
ProfRob
CC BY-SA 4.0
2018-12-03T20:50:31.853Z
Have a look at https://astrobites.org/2015/06/09/hold-on-to-your-moons-ice-atmospheres-and-the-grand-tack/
ProfRob
CC BY-SA 4.0
2018-12-03T22:06:01.597Z
This is a question of when and where the sub-Jovian disc forms, from which the moons are born. But in the current literature there is essentially no model that can make Jupiter grow without making the sub-Jovian disc grow, so most people working on this think that the (regular) moons + gas giants have formed from the same material. Different story for the irregular satellites.
AtmosphericPrisonEscape
CC BY-SA 4.0
2018-12-04T00:40:55.537Z
@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.
userLTK
<natural-satellites><planetary-formation><orbital-migration>
Moons of migrated giant planets: Icy, Rocky, or none at all?
Arkenstein XII
# Moons of migrated giant planets: Icy, Rocky, or none at all?

(Asked by: username_0 on 2018-12-03)

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?

**Tags:** natural-satellites, planetary-formation, orbital-migration

> **Comments:**
> **username_1**: This is supposed to have happened to Jupiter, so there's your answer  
> **username_1**: Or are you referring to "hot Jupiters"?  
> **username_0**: @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?  
> **username_1**: Yes! That is the current thinking - see Grand Tack Hypothesis. https://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.  
> **username_0**: @RobJeffries Fascinating! That would suggest that the Jovian moons came with Jupiter all the way in, and all the way back out. I think that answers my question pretty succinctly. I realise that we have no observational data beyond our own back yard, I was just curious whether there had been any modelling that suggested whether moons would be kicked out of their orbits or not.  
> **username_1**: 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.  
> **username_1**: Have a look at https://astrobites.org/2015/06/09/hold-on-to-your-moons-ice-atmospheres-and-the-grand-tack/  
> **username_2**: This is a question of when and where the sub-Jovian disc forms, from which the moons are born. But in the current literature there is essentially no model that can make Jupiter grow without making the sub-Jovian disc grow, so most people working on this think that the (regular) moons + gas giants have formed from the same material. Different story for the irregular satellites.  
> **username_3**: @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.  

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