Planet - moon - satellite questions

[Stink Fish Pot]

As far as I know, there are no instances of a moon having its own moon in our solar system.

Is this something that cannot be created because of the gravitational pull of the largest nearby body, or is this something that would be possible given the right circumstances?

It appears, based solely on observing our universe, that the development of the first order moon is rather trivial. But since there are no examples of the second order moon I'm asking about in our solar system, is it simply impossible to form?

If something of the correct size slammed into our moon today, could the resulting debris possibly form a moon for the moon, or would it end up as a second moon for earth, a faint ring for the earth, or just fall back onto the moon?

Capturing a second level moon is also something we can discuss, although I'd think this to be almost impossible given the gravitational pull of the moons parent planet.

Also, with the discovery of new planets around nearby stars, have we been able to detect if these planets have moons, or are the distances so great that detail of this level is currently impossible to detect?

[John Mace]

Physically possible, yes. But you'd need the right conditions with the first moon being rather far from the planet.

[Andy L]

Originally Posted by Stink Fish Pot

As far as I know, there are no instances of a moon having its own moon in our solar system.

Is this something that cannot be created because of the gravitational pull of the largest nearby body, or is this something that would be possible given the right circumstances?

It appears, based solely on observing our universe, that the development of the first order moon is rather trivial. But since there are no examples of the second order moon I'm asking about in our solar system, is it simply impossible to form?

If something of the correct size slammed into our moon today, could the resulting debris possibly form a moon for the moon, or would it end up as a second moon for earth, a faint ring for the earth, or just fall back onto the moon?

Capturing a second level moon is also something we can discuss, although I'd think this to be almost impossible given the gravitational pull of the moons parent planet.

Also, with the discovery of new planets around nearby stars, have we been able to detect if these planets have moons, or are the distances so great that detail of this level is currently impossible to detect?

A second order moon is very likely to be in an unstable orbit.

Fact 1: In order to orbit the moon and not the planet, the 2nd-order moon would have to be within the moon's Hill Sphere http://en.wikipedia.org/wiki/Hill_sphere . Small moons have a Hill sphere smaller than the moon itself and so can't have a satellite in stable orbit.

Fact 2: An object that that is below its primary's "geosynch" orbit, will experience tidal deceleration, and will eventually crash into the primary.

Fact 3: Many moons are tidally locked to the planet they orbit (like our moon is) so the geosynch orbit is far outside the Hill sphere, and any moon they did get would crash pretty soon.

Therefore, you're not likely to find many moons with secondary moons - they can happen but will tend to be short lived.

Interesting link http://curious.astro.cornell.edu/que...php?number=679

[Gagundathar]

Wow. Great answer. Thanks for the links.

[Chronos]

I think I have heard of one example of this among the asteroids, though.

[dtilque]

Originally Posted by Stink Fish Pot

Also, with the discovery of new planets around nearby stars, have we been able to detect if these planets have moons, or are the distances so great that detail of this level is currently impossible to detect?

It's not impossible and there's at least one astronomer who is trying.

The technique he's planning on using will only work on planets that transit their stars. A moon will be too small to detect the decreased light as we do with planets, but a large satellite of a planet may change the timing of the planet's transit. Depending on it's position in its orbit, the moon may cause the transit to happen 1) a little bit earlier, 2) a little bit later, 3) last a little longer or 4) end a little sooner. If it's between those four positions, there will be lesser effects.

In order to find a moon with this technique, they'll have to time a large number of transits and do a mathematical analysis on it. Multiple large moons (such as Jupiter has) will probably make the analysis harder and I expect require even more transits.

[Enola Straight]

http://boards.straightdope.com/sdmb/...highlight=moon