Yes Helio. Certainly the 116 years of telescope observations starting in 1891 as reported in Sky & Telescope of the migrations of the Galilean moons could be interpreted like this. Models developed to show their long age integration in their present orbits contain many assumptions.
Yes, all science (and engineering) require initial conditions. Assumptions are suppositions and they are typically what comes prior to conjectures, then hypotheses, then if they are overarching in scope, theories.
What helps weed out the bad assumptions is having multiple lines of evidence. So an assumption or assumptions can bring forth a scientific model if it has objective evidence giving it weight.
The most popular model, I think, for the moons of Jupiter can be summarized (I hope
):
1) Jupiter was in a very dense part of the early solar accretion disk. The fact that it was just outside the snowline means it had all those ices to build from.
2) The moons formed at the same time in this very dense gas and dust accretion region, especially as the accretion disk for Jupiter formed.
3) The gas and dust, being very small, had slower rates in the orbit around Jupiter, similar to that of the solar disk.
4) As clumps formed into large objects (moons) they lost a lot of their orbital suspension and began to spiral inward toward Jupiter.
5) As long as the disk was still around, these newly formed moons augured into Jupiter.
6) The EM dynamics of Jupiter's core created a hole, or void, region around itself.
7) Io, in its inward spiral, was the first to benefit from the void and it settled into orbit, though it would then begin to migrate outwarrd due to tidal action.
8) Europa was still spiraling inward but fell into resonance with Io.
9) Ganymede did the same with Europa, along with resonance assistance from Io.
10) Callisto came "late to the party" and the gas and dust were dissipated to the point where it didn't reach a resonance orbit with the others.
11) The resonance dampened the formation of circular orbits, thus eccentricity exists.
12) The eccentricity increase the heating, so temperatures of, say, Europa are high enough to have a huge briny ocean. [The less briny water is less dense, which rises and freezes forming an ice cap.]
13) Jupiter's tidal action, caused by its fast rotation rate, drags Io along in its orbit causing it to speed up, thus causing it to migrate outward.
14) The rate of movement is dampened since it must also drag the other two sisters along due to the resonance, though they too are pushed forward by tidal actions, but the force is an inverse cube law so distance makes a big difference.
I doubt you will find many who will claim Io is now spiraling inward, It's plausible that circumstances over eons have affected that resonance in accord with the paper you cite, but show my a paper that predicts Io will crash burn. That would be interesting to see but seems, IMO, to be an ATM point of view.
Example.
Following the scenario depicted by Canup & Ward (2002), Ganymede underwent the faster Type I migration because of its larger mass. Moving toward Jupiter, it first captured Europa in resonance, followed by Io, and this process happened relatively quickly (about 10^5 years). After the dissipation of the disk, the satellites then reached their current state by tidal dissipation.",
Ok, notice that this is another model in how they got into resonance. But I like the one above, which comes from Erik Asphaug (Planetary Science, U of Arizona)
Neither model is arguing that Io will auger in, or am I wrong?
"ABSTRACT Context. The Galilean satellites have very complex orbital dynamics due to the mean-motion resonances and the tidal forces acting in the system.
Yes, this gets more into your point about assumptions. The problem, I think, for calculation tidal forces is to fully understand all the numerous structural variables of the spinning host. If you start with a perfectly spherical planet made of perfectly rigid material, say less flexible than diamond, then the tidal action will be nothing, at least I think this is correct.
The flexing of the surface and subsurface layers, the variations in density by both latitude and longitude, the sloshing effects of resonant things like bays (eg Bay of Funday), the regional flows, etc. all contribute to the amount of tidal action on the moon. Then all these variables must be applied to the moon as well, as well as, the orbital resonance effects.
The more we learn about Jupiter's interior the more we will be able to apply retrodictive science to the moons of Jupiter.
There are stories out now about the discovery that Titan's migration (outward) is perhaps 10x what they held it to be, though others had predicted it would be greater. The complexity of Saturn's internal structure, including its atmospheric flows, is mostly the challenge to all the assumptions in the earlier model.
Jupiter's Galilean moons like Earth's Moon has tidal dissipation rate issues. if there is no giant impact model for the Moon, the current tidal dissipation rate shows the Moon kissing the Earth only 1.5 billion years ago.
Nope. Given all the variables, the migration rate of the Moon is a very crude way to give the Moon any age, only a minimum. If you divide its distance by its annual migration rate outward, 3.8 cm/yr., it gives the Moon a 10 billion year history. But, another variable is that inverse cube law for tidal action, so when the Moon was much closer, it would have been migrating at a much faster rate. All one needs to know are those thousands of density variations, sloshing resonances, etc. to calculate the age based on the refined equations.
Fortunately, as mentioned at the beginning, we have multiple lines of independent evidence to do a better job on determining the Moon's age. The craters of the Moon are such that they argue for the Moon being around for the Heavy Bombardment period long ago, so it has to be at least that old. Also, the samples from Apollo also demonstrate an even greater age. There are probably other lines of evidence as well.
So young Galilean moons like young Saturn ring age - looks like recent catastrophism in the solar system
No, they are stating that the resonant stability will be for 1.5 Gyrs. I didn't search hard -- though the word "age" isn't in that paper -- that would indicate they suggest the moons are young.
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