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randtek
2005-Feb-20, 12:52 PM
Based on current accepted theories of planetary dynamics, is it possible for a large moon of planet (Titan for example) to have a moon or moons of it's own?

If so, are there any known examples?

Please excuse me if this seems like a silly question. I am not an astronomer, just a lover of star gazing!

ChromeStar
2005-Feb-20, 01:00 PM
Welcome to UT randtek


Please excuse me if this seems like a silly question. I am not an astronomer, just a lover of star gazing!

It's actually a damn good one... Lol ;) - No question is stupid or silly


... is it possible for a large moon of planet (Titan for example) to have a moon or moons of it's own?

I don't think it would be called a moon seeing as - as far as i know - a moon is an object smaller then the planet it orbits, and only orbits a planet. So my guess is that they would be called satelites, not moons.

Hope this helps
ChromeStar :)

Nyrath
2005-Feb-20, 01:00 PM
Apparently astronomers have yet to detect any (http://www.timesonline.co.uk/article/0,,564-1467554,00.html). The current explanation is that such an arrangement is not gravitationally stable.

Betelgeuse
2005-Feb-20, 01:18 PM
I'm not sure about moons having moons, but I know that asteroids can have moons! Some of the larger asteroids in our solar system actually do have disovered moons. From what I've read, in 1993, an tiny moon called Dactyl was discovered orbiting Ida. You've probably heard of the large asteroid, Ida. This moon, called Dactyl is only about 1 mile wide in comparrison with Ida which is about 19 miles across. But, yes, many moons have been discovered orbiting asteroids - Petit-Prince was discovered orbiting the 135 mile wide asteroid called Eugenia. And then, in 2000, the 90 mile wide asteroid called Pulcova was discovered to have its own moon that's about nine miles wide.

But, about moons having moons....well, I'll have to get back to you!

antoniseb
2005-Feb-20, 05:05 PM
This is mostly just a question of terminology. The Smart 1 probe is currently orbiting our Moon. I would normally call it a satellite of the moon. For some definitions of the word moon you could say Smart 1 is a moon of the Moon.

As I have said in the several threads about whether Pluto or Sedna are planets, I think that there is no need to worry about it much. If you are speaking to anyone and call something orbiting something orbiting a planet a moon of a moon, no one will misunderstand what you are saying. Since you have then successfully conveyed the idea, it must be that the language construct worked.

If there is later some set of technical definitions passed to us all from the scientists of the world as to when you call something a moon vs. when you call it a satellite, or a planet, or something else, we'll be able to give you a yes or no answer.

eburacum45
2005-Feb-20, 07:05 PM
I think the main problem is that this arrangement could not arise naturally. It is possible for a panet and a moon to capture another body; but it would end up orbiting the larger body in almost every case. Smart1 and all man made Lunar satellites achieve a stable orbit by firing their motors as they approach the Moon.
This would not happen in nature very often...

antoniseb
2005-Feb-20, 07:34 PM
Originally posted by eburacum45@Feb 20 2005, 07:05 PM
This would not happen in nature very often...
If a large object were to smash into Callisto much the way some large object hit the Earth 4.4 billion years ago, a moon like ours could form around Callisto. I don't think such a situation is all that unique. There are many ways that the Jovian system is like a miniature solar system.

zephyr46
2005-Feb-21, 02:33 AM
A/CC list of binary objects (http://www.hohmanntransfer.com/topics.htm)

I think Castor 6 (http://www.solstation.com/stars2/castor6.htm) is an example of what is possible,


The Castor system has as many as four bluish-white, main sequence stars and two known, fainter red dwarf companions

To my knowledge, There is no known moons of moons, apart from artificial satelites like Smart 1.

StarLab
2005-Feb-21, 02:49 AM
In my terminology, there are four degrees of planetary revolution:

1st - stars in relation to each other
2nd - planets around stars
3rd - satellites around planets
4th - satellites around satellites

Now such situations such as Ida/Dactyl are extraneous exceptions, and I'm more convinced of classifying Dactyl as a 3rd degree moon, but a 4th degree is not physically impossible.

antoniseb
2005-Feb-21, 02:56 AM
Originally posted by StarLab@Feb 21 2005, 02:49 AM
In my terminology...
You can use whatever terminology you like, but if you're hanging out with a bunch of astronomers and casually say something like "a 3rd degree moon", you might get some blank stares, and you won't have conveyed your message very well.

Svemir
2005-Feb-21, 07:01 AM
There are no known moons of the moons in our planetary system because it,s very old (4,5 bio. years) and such formations are not stable according to current theory of planet formation (accretion discs).
IMHO (or "theory") planets and their moons forms by ejection from parent star.
The system of a planet and it's moons forms at the same time and moons of the moons can be formed but because the system is unstable it could be observed only when the system is very young.
So, we have to look at the extrasolar young systems to find moons of the moons which is rather difficult.

I'm not sure about moons having moons, but I know that asteroids can have moons!
Tom van Flandern on its website metaresearch.org use this fact to endorce his theory of exploding planets. I don't believe in exploding planets (after all , we are still here), but I do think that such formation does not support accretion theory.

eburacum45
2005-Feb-21, 05:58 PM
Originally posted by antoniseb@Feb 20 2005, 07:34 PM
If a large object were to smash into Callisto much the way some large object hit the Earth 4.4 billion years ago, a moon like ours could form around Callisto. I don't think such a situation is all that unique. There are many ways that the Jovian system is like a miniature solar system.
Good point.
However the Jovian system is a little too crowded for the retention of such a satellite; the Gallilean moons are constantly pulling at each other.

On the other hand, Titan is a better candidate, as it is accompanied by comparatively small moons.

Still there are no examples of this phenomenon known anywhere. Yet.

zephyr46
2005-Feb-22, 03:16 AM
Starlab, what are Co-orbitals in your terminology?


Club 1AU Asteroids sharing Earth's orbit
There could be "Trojan" asteroids sharing Earth's orbit at the L4 and L5 Lagrange points, like those that share the orbits of Mars and especially Jupiter (see MPC lists). If there are, they will be very hard to spot from the ground. See David Tholen's comments about Trojans in the 24 March 2000 Cambridge Conference Correspondence, and Paul Wiegert's Earth Lagrange/Trojan asteroids page.
Three very small objects, 1991 VG, 1999 CG9, and 2000 SG344, have been spotted with orbits calculated to be so much like the Earth's that they may be artifacts such as J002E3, which appears to be an Apollo rocket stage, or, in CG9's case, may be a chunk of the Moon.
And then there is 3753 Cruithne, which has a bizarre "horseshoe" orbit of 1:1 mean resonance that makes it a very unusual companion of the Earth. Being a companion would otherwise require being a satellite (circling the Earth like the Moon) or a Trojan (following or trailing the Earth in the Earth's own orbit at +/- 60 nodes).
According to those who have studied Cruithne, other candidates for a similar Earth companion status are 1998 UP1 and 54509 2000 PH5. Separately, in an Icarus article, Helena M. Morais and Allesandro M. Morbidelli footnoted that they calculated 1998 UP1 could become such an object, as well as 2000 WN10. They also said that 2002 AA29 appears to be one now, but temporarily.
In their Oct. 2002 Meteoritics & Planetary Sciences article, Martin Connors et al. report that 2002 AA29 is the most truly co-orbital Earth companion asteroid yet found, and that it occasionally transitions into and out of being a natural satellite orbiting the Earth. See A/CC News for more about this story.

From Taxonomy of minor objects by orbit, spectral class, families, groups (http://www.hohmanntransfer.com/topics.htm#taxon)

Sorry about the length guys, but this is one of my fav desriptions of some of the most interesting orbital dynamics I know of, check out the link for more on each of the posts.

Jakenorrish
2005-Feb-24, 05:03 PM
With a universe the size of ours, I would be very surprised if conditions didn't exist somewhere in it for an object orbitting a gas giant perhaps at quite a distance couldn't have a moon of its own (even if it was for a relatively short period of time).

We have discovered extrasolar planets which by comparison to our largest planet (Jupiter) that are huge, so if a large moon were orbitting it at a distance, then why not? By all means throw some mathematics into the equation to make it seem unlikely, but they certainly don't disprove the possibility.

I think that by taking our solar system as a model, then we can safely say that it is unlikely for it to happen here, but outside of it, who knows!!!!

ChromeStar
2005-Feb-27, 04:00 PM
You can use whatever terminology you like, but if you're hanging out with a bunch of astronomers and casually say something like "a 3rd degree moon", you might get some blank stares, and you won't have conveyed your message very well.


Haha :P :lol: :P :lol: ;) :D