Is it physically possible for a huge Jupiter-like exoplanet to harbor this kind of moon? Could have been formed in the protoplanetary disk or could be Neptune-like planets that have been trapped during migration towards to, or away from, the central star?
Sandro,
I'm not familiar with the term 'gas moon'. Do you mean a satellite that has no solid component? If so, then the Roche limit would be exceedingly large for such a body - as it is strengthless. Not sure that that would lead to a viable orbit around the planet or not.
I see no reason why a Gas Giant binary could not exist, although nature does not appear to strongly favor this, at least in the exoplanet systems we have seen to date. There is clearly a limit, of a sort - a gas giant needs to be of a certain (large) size. If it is a moon, that implies its parent is larger. Jupiter is not too far from being a star; if it were the smaller satellite of an even larger gas giant, then there would be a real risk that the larger body would not be a planet, but a star (and, we know there are lots of binary stars, and some have planets, possibly including Alpha Centauri B).
Yes James, I have in mind to kind of gaseous moons. One could be a type of gaseous moon that have a rocky or metalic core, which may have formed on the edge of the protoplanetary disk and then have migrated inward, the other could be only gas, without solid core, but perhaps this is more rare and improbable. My question is if within the laws of physics and thermodynamics, we could model and concive the formation and existence of a gaseous moon, and how much we are close or far from be sure that something like this could exist.
As Astrobiologist with Biological background, I’m trying to understand this topic. I have read many papers about planetary formation and migration, but I haven’t found an answer to this. I consider that this could be important to Searching of Life and Habitable planets purposes, because if gaseous moons don’t exist, then more rocky moons exist, likely new kinds of rocky moons that could harbor Life or could be Habitable (for us or especially for our microbial Life).
Yes Marshall, I understand the uncertainity that we have about brown dwarfs. I understand that the volume of a brown dwarf, depends of their mass. This volume could be of 10 to 90 Jupiter masses, but as its volume is governed whether by Coulomb pressure or by electron-degeneracy pressure, the radii of brown dwarfs vary by only 10–15%, making it difficult to distinguishing them from planets just by its radii. In our solar system, Saturn is nearly as large as Jupiter, despite having only 30% the mass. The International Astronomical Union considers that an object under 13 Jupiter masses is a planet. This is why I wonder if huge Jupiter-Like planets, could have larger rocky moons, even gaseous moons. Also, I was thinking in a Jupiter-Like planet or brown dwarf that was expelled from its solar system with some Neptune-like planets or moons, whether trapped by or originated with this object before the expulsion.
I see no reason why a 10 Jupiter mass primary could not have a 1 Saturn mass satellite - that would be comparable to the Earth - Moon mass ratio. As for how likely that would be, I think that could only be resolved by observation, given the poor ability of theory to predict the observed exo-planetary systems.
@Marshall: I think Jupiter is very far from being a star. At 13 Jupiter masses, it could become a brown dwarf, a very weak/ first incarnation of a star like body, so Jupiter is still far away from it.
@topic in general: Considering our little knowledge about planetary formation (especially regarding gas giants, whose inner structure is still very open for debate), it is difficult to answer this question, but basically: why not? There are many instances where multi-star systems evolve, often of different sizes (most multi-system have a very unequal mass distribution), so I think it is plausible to assume that there are systems where the gaseous mass is not sufficient to form multiple stars, but maybe a system of gas giants and gas moons.
We also have several examples of gas giant moons with volatiles (e.g. enceladus and Europa having sub-ice oceans) and one of them even has a very thick atmosphere (Titan). It is also possible that a very large gas giant captures a smaller one in earlier phases of planetary system formation.
http://en.wikipedia.org/wiki/Roche_limit Here you find the formula for a "fluid" satellite, so why not make an example calculation - at what point and mass distribution would a large gas giant be able to have a satellite that is similar to Neptune, Uranus, Saturn and Jupiter. What would the possible minimum radius be and does it concurr with the sphere of influence of the parent body. If that is the case, I think there is no reason why it should not work. I would do the calculation, but right now, I am short on time.
This recent detection of an Earth-mass, probably gaseous, exoplanet might be relevant - see http://www.nature.com/news/earth-mass-exoplanet-is-no-earth-twin-1.14477.
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