How do the tidal forces warming moons theories hold when []

In summary, the theory of tidal forces heating moons suggests that the energy comes from the rotational and orbital kinetic energies of the system. As the moons continue to orbit and rotate, the tidal forces cause them to heat up, but this heat is dissipated through thermal radiation. The energy is ultimately sourced from the host's rotation, causing the moons to slowly spiral outwards. This process can lead to tidal locking and changes in the orbital periods of the moons. Whether this process occurs with lone moons or is accelerated by the presence of multiple moons is still being studied.
  • #1
cdux
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How do the “tidal forces warming moons” theories hold when [..]

How do the “tidal forces warming moons” theories hold when apart from heating from expansion, there may be also cooling from contraction?

I can understand a temporary heating, from the tital forces exerted on the moon but wouldn't there be cooling as well eventually when particles "give in" to contraction? Wouldn't they eventually net a unchanging whole body temperature? i.e. How can Europa's oceans be warmed by that and how can Io's crust be melted by that?
 
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  • #2


Well, can you make your hands colder by vigorously rubbing them together?
 
  • #3


The heat generated by the tidal forces is dissipated mostly, if not completely, by thermal radiation emitted by the moon. But still, this requires that the temperature of the moon increases until the amount of heat lost through thermal radiation is equal to the heat generated by all methods inside the moon. So the net effect is a warmer moon.
 
  • #4


Bandersnatch said:
Well, can you make your hands colder by vigorously rubbing them together?

But where does the energy come from? There's a human rubbing there. I thought an orbit recycles it on turning. Does it actually drop slightly from orbit?
 
  • #5


let me use an analogy to explain this.

you stretch a piece of rubber. due to internal friction it heats up. when it relaxes back, it does not cool back down! this is because the heat has dissipated.

the stretching of a planet is exactly the same - a shear force on a viscoelastic material. you can think of it as squeezing and stretching a tennis ball filled with jelly.
 
  • #6


chill_factor said:
let me use an analogy to explain this.

you stretch a piece of rubber. due to internal friction it heats up. when it relaxes back, it does not cool back down! this is because the heat has dissipated.

the stretching of a planet is exactly the same - a shear force on a viscoelastic material. you can think of it as squeezing and stretching a tennis ball filled with jelly.
Yes but what "gave in" to give that energy? The internal structure of the planet, the orbit?

[Because surely, tidal forces alone can not produce energy since an orbit is in its basic sense only recycling energy.]
 
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  • #7


cdux said:
Yes but what "gave in" to give that energy? The internal structure of the planet, the orbit?

[Because surely, tidal forces alone can not produce energy since an orbit is in its basic sense only recycling energy.]

I believe it steals energy from the orbit of the Moon.
 
  • #8


Yes, the energy comes from rotational and orbital kinetic energies of the system. As the tidal deformation heats up the satellites, their orbital and rotation periods change until the orbits fully circulate and the moons themselves get tidally locked.

With multiple bodies as in the case of Jovian moons, the situation might get a bit more complicated, but it's still the case of orbital and rotational energy dissipation.

Here's an excerpt from the abstract of C.F.Yoder's "How tidal heating in Io drives the Galilean orbital resonance locks"(http://adsabs.harvard.edu/abs/1979Natur.279..767Y)
According to the proposed model, initially all three satellites{Io, Europa, Ganymede} are in orbits far from the 2:1 commensurabilities or the three body lock. The tide raised on Io damps down the free eccentricity; only modest tidal heating occurs. Subsequently the dissipative tide raised on Jupiter by Io causes Io's orbit to spiral outwards; Io approaches the 2:1 commensurability with Europa. Io's forced eccentricity increases rapidly to a critical value, and thereafter the resonant interaction causes Europa's orbit to expand at half that of Io's orbit. A fluid core is probably formed as the result of tidal heating. Finally Europa approaches the 2:1 commensurability, angular momentum is transferred from Europa's orbit to Ganymede's, and a steady state is attained.
 
  • #9


Is it an inevitable fate of all theoretically isolated but naturally structured bodies to be heating up while dropping on their host (even if that heating up or drop is negligible for humanely observable periods)?

Now I wonder if some 'unexplained deaths' of nearby planets were that phenomenon in a slower scale. Maybe a negligible heating up but a sizable drop of orbit over eons.
 
  • #10


What do you mean by "drop of orbit"?
 
  • #11


Giving up of gravitational potential energy. The distance times mass times g thing.
 
  • #12


cdux said:
But where does the energy come from? There's a human rubbing there. I thought an orbit recycles it on turning. Does it actually drop slightly from orbit?
No, it's the other way around. Io, Europa, and Ganymede are slowly spiraling out from Jupiter. The orbital period of the fastest of them, Io, is over four Jovian days. This means they should be migrating outward, not inward.

So where does the energy come from? Ultimately, from Jupiter's rotation. Those moons are slowly slowing down Jupiter's rotation rate.
 
  • #13


That also works, of course.

Do some of them spiral out because of the local coincidence of the multitude of them and they would not if they were the only moons, or another process is afoot?

Now I wonder how do they slow it down. Is it the complex system of the multiple of moons of would it happen with lone moons?

And isn't the slowing of the rotational rate of the host relative to a moon's?
 

1. How do tidal forces cause warming in moons?

When a moon orbits a planet, the planet's gravitational pull creates tidal forces on the moon. These tidal forces cause the moon's surface to bulge and stretch, generating friction and heat. This heat is what causes the moon to warm up.

2. Do all moons experience tidal forces and warming?

Yes, all moons that orbit a planet experience tidal forces to some degree. However, the amount of warming caused by these forces depends on a variety of factors, such as the moon's distance from the planet and its composition.

3. How do the tidal forces vary on different moons?

The strength of tidal forces varies depending on the moon's distance from the planet, the size and mass of the planet, and the composition and density of the moon. For example, a moon closer to its planet will experience stronger tidal forces than a moon farther away.

4. Are there any other factors that contribute to moon warming?

Yes, there are other factors that can contribute to moon warming, such as internal heating from radioactive decay or impacts from other objects. However, tidal forces are often the main factor in causing warming in moons.

5. How do the theories about tidal forces and moon warming hold up against observations?

Overall, the theories about tidal forces causing moon warming have been supported by observations. For example, the moon Io, which experiences strong tidal forces from Jupiter, has a very active and volcanic surface due to the heating from these forces. However, there is still ongoing research and study to better understand the complex interactions between tidal forces, moon composition, and other factors.

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