Seems like you nailed it.

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Hey cool! Thanks for the link (amazing what's on Wiki these days...).

@ Tony: Thanks to you too. I presume your sim had the moon in its standard orbit - which is why the farther particles got flung?

FWIW: My thought experiment doesn't require reference to current theories of our moon's formation. My theoretical planet wouldn't necessarily have had to acquire its moons in the same way Earth did. As far as I know, none of the other planet's moons require an impactor-theory to describe why they have moons in the first place.

I am only guessing, but they probably got their moons through a capture process or as left over material from the planet's own formation that did not get absorbed into the planet itself. Something similar could account for the two-moon system I describe in the OP.

Your thoughts on retrograde moons is interesting, and something I hadn't thought about, considering there is only one or two moons (IIRC) in our solar system that have retrograde motion.

Doesn't retrograde capture require flinging another similarly sized object out of the planetary orbit?

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Jump in with both feet!
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"Are you a mad-hatter that just types what he wishes, or have you actually any physics training?"
Occam's Ghost to Grant Hutchison.

Eighty-nine, by my quick count. Jupiter alone has 48 retrograde moons.
In fact, most of the outer moons of all the giant planets are retrograde: as Tony says, retrograde orbits are more stable, so they can persist at distances where direct orbits are unstable.

Grant Hutchison

Amazing what you learn when you blindly assert. Thanks for the update!

(I knew about Triton, but thought it was relatively unique. After your post, I googled and read the Wiki...)

__________________
Talent develops in quiet places, character in the full current of human life.
- Goethe

Jump in with both feet!
- Me, indulging my inner eight-year-old

*** *** ***

"Are you a mad-hatter that just types what he wishes, or have you actually any physics training?"
Occam's Ghost to Grant Hutchison.

So it would be not unreasonable to have an Earth-sized planet with two moons, one at 140K and one at 380K? Or one at 50K and one at 380K?

How about orbital periods for these worlds? Using this calculator
http://www.ajdesigner.com/phpgravity...ion_period.php
I get a period of about 1.3 days for the 50Kmoon, and about 6 days for the 140K moon. But that calculator assumes the moons are massless, I think.

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Okay, using Earth time scales here, could the second moon have been a captured body, like Ceres where it only exists as part of the system for about 100,000 years? It just happens to be the 100,000 year period where civilization developed.

Or could a it be captured after recorded history had begun? I'm thinking here of a system where a culture, say in the Bronze Age, had one sun and one moon and had all the appropriate myths in place, then all of the sudden this other moon swoops in and begins to assert control over the "established truths". What effect would that have had?

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She might. You never know.

Either way, I'm seeing a strong influence on culture via religion, mythology, what have you.

If the moons are with the planet from around formation - every society will have a tradition that accounts for two peers to the sun god.

If the moon is a later capture, every society will have a tradition regarding the arrival of the Destroyer (presuming the new moon is not, in fact massless, its arrival will change the planet's tidal system; considering most people live in the littorals, the tides will affect them pretty strongly).

__________________
Talent develops in quiet places, character in the full current of human life.
- Goethe

Jump in with both feet!
- Me, indulging my inner eight-year-old

*** *** ***

"Are you a mad-hatter that just types what he wishes, or have you actually any physics training?"
Occam's Ghost to Grant Hutchison.

It's amazing what can occasionally be had through intuition.

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Heinlein's: "Staying young requires the unceasing cultivation of the ability to unlearn old falsehoods." "Freedom begins when you tell Ms. Grundy to go fly a kite."

Actually, this happened last year, but the additional moon was only about 4 meters across, and only stuck around for a few months. That's the biggest problem with this scenerio, with rare exception, a captured moon is not that stable:
http://www.orbitsimulator.com/cgi-bi...num=1182030550

I've never seen that link. Thanks. I've got my own collection of calculators I wrote, including a period calculator here: http://orbitsimulator.com/formulas . Mine has nicer units of mass

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Nice calculators, Tony! I'll add them to our list at OA.

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