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Thread: Powering Io

  1. #1
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    Powering Io

    I do not believe in perpetual motion. Something is powering Io (namely tidal flexing) and the energy of all those volcanoes has to come from somewhere. That somewhere has to run out eventually (assuming nothing intervenes first). What is it and when will it run out?
    SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS

  2. #2
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    It's being powered by gravitational interaction with the nearby satellites (particularly the resonance with Europa and Ganymede), which constantly keeps Io's orbit from circularizing, and so makes it subject to tidal effects from Jupiter as it librates. The energy is coming from the kinetic and potential energy of the other satellites, the orbits of which are decaying slightly as a result. There's a lot of energy left.

    Grant Hutchison

  3. #3
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    I suspect that Tom means that these decaying orbits can't last forever. The energy coming out of the volcanoes is lost as waste heat; eventually these losses will cause Io to fall into Jupiter. I don't think that will happen for many billions of years. Or maybe the outer satellites will get so close together that they will start colliding.

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    Let's not forget that tidal interaction with Jupiter will tend to push the orbits out while the planet gradually slows down. I would not be quick to infer that the moons would be falling in now.

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    Quote Originally Posted by Hornblower View Post
    Let's not forget that tidal interaction with Jupiter will tend to push the orbits out while the planet gradually slows down. I would not be quick to infer that the moons would be falling in now.
    Yes, the theories of how the Io/Europa/Ganymede resonance originated include versions in which Io evolved outwards to resonance with Europa, after which the pair evolved outwards to resonance with Ganymede. There seem to be enough different theories that I doubt if we can say how the system will continue to evolve on the million-year timescale that would answer the second part of Tom Mazanec's question.

    Grant Hutchison

  6. #6
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    In that case, the energy would come from Jupiter's spin. Certainly there is no such thing as a free lunch, but in some cases it is possible to extract useful energy from a system for a long time without breaking the bank.

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    Quote Originally Posted by eburacum45 View Post
    In that case, the energy would come from Jupiter's spin. Certainly there is no such thing as a free lunch, but in some cases it is possible to extract useful energy from a system for a long time without breaking the bank.
    Even if the orbits are decaying, some/most/almost all of the energy still comes from Jupiter's spin - the outer satellites transfer orbital energy to Io, while gaining energy by tidal interaction with Jupiter.

    Grant Hutchison

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    So it will be when they get into resonance with Callisto that the fun ends?
    SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS

  9. #9
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    Quote Originally Posted by Tom Mazanec View Post
    So it will be when they get into resonance with Callisto that the fun ends?
    Or begins.
    The Galilean satellites' evolution toward a 4-body mean motion resonance.

    It's a chaotic encounter in 2 Gyr, which may or may not settle into a MMR. The trouble with these chaotic encounters is that (duh) they depend so strongly on initial parameters. So if we're off just a little on our estimate of Jupiter's tidal dissipation factor, for instance, everything could be different in a few billion years' time.

    Grant Hutchison

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