William Taylor wrote:
>
>> BTW, with the Laplace resonance the three moons would
>> _never_ be seen close in the sky. So, Jijoans could say
>> something like "when the three moons are full" or
>> "when the three moons rise" to signify "never" :-)
>
> Well that proves I'm not doing well tonight. I'm on
> the computer cuz I can't do much else with a headace.
> I jumbled things up in my head and thought that
> the moons moved in a ratio to each other.
>
But they do O:-)
> Wrong use of resonance.
>
The Laplace resonance is a "higher level" of resonance.
What happens is this: any two decent moons [and I don't
know if an Earth-like planet can have a decent moon...]
would lose orbital energy due to the mutual iteractions
etc [causing them to change shape back and forward,
transforming mechanical energy into thermical energy,
etc]. So, eventually, their orbital periods would be
commensurate. At this point [depending, of course,
on how big their masses are!], their periods would be
locked forever in this ratio.
Add a third moon to this system. When this third moon
gets into the resonance, the three moon system becomes
even more stabilized than before. And the three-moon
configuration is such that it repeats periodically.
This happened to Io-Europa-Ganimede. It's predicted that
Calisto will eventually join those three in their resonance,
but I don't know when and how :-)
Alberto Monteiro
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