PDA

View Full Version : Saturnian Satellite System



EDG
2009-Mar-10, 06:38 AM
Wikipedia shows the distribution of mass in a satellite system as a pie chart, which really brings out something that's bugged me for ages.


If we look at Jupiter's (regular) satellite system, we see four bodies that are roughly similar in size and mass:

http://upload.wikimedia.org/wikipedia/en/thumb/0/01/Masses_of_Jovian_moons.png/300px-Masses_of_Jovian_moons.png

If we look at the Uranian satellite system, we see five bodies that again are roughly similar in size (OK, Miranda is somewhat smaller, but it's bigger than the irregular satellites at least):

http://upload.wikimedia.org/wikipedia/en/thumb/0/02/Masses_of_Uranian_moons.png/180px-Masses_of_Uranian_moons.png

I consider Neptune's system to be a bit strange since it has one retrograde major satellite and the rest are tiny iceballs. I'm not sure that we're looking at the original satellite system it had, especially if Triton was a captured body. So I don't think it's a valid comparison for this discussion:

http://upload.wikimedia.org/wikipedia/en/0/07/Masses_of_Neptunian_moons.png

But Saturn's system is odd - it has one large satellite and lots of small ones (and many more really tiny ones):

http://upload.wikimedia.org/wikipedia/en/thumb/a/a0/Masses_of_Saturnian_moons.png/300px-Masses_of_Saturnian_moons.png

I realise we only have a sample of four systems here, but do we have any idea (based on satellite formation theories) why Saturn's is dominated by one big satellite and the mass in Jupiter's and Uranus' system is more evenly distributed? Titan isn't considered to be a captured body so I suspect the similarity to the Neptunian pie chart is just coincidental. Could it be something to do with Saturn's size? Or is it just random happenstance, and any of the gas giants could have had a system that looked like Saturn's with lots of small satellites and one (or two) much larger ones?

Sticks
2009-Mar-10, 04:16 PM
EDG_ I have locked the duplicate thread as you requested

However you hot linked several images in violation of the forum rules (http://www.bautforum.com/forum-rules-faqs-information/32864-rules-posting-board.html)



8. Hotlinking

Try to avoid putting in links to images directly from someone else's website. This can add a lot to their bandwidth, and then the host has to pay for it. In other words, if you see an image you like on an astronomy site, put in a link to that site, but don't use the [IMG] tags so the image loads into your post from their site directly. If you really want an image in your post, put it in a public site someplace and link to it from there. One exception would be from sites like NASA or universities, where bandwidth is not such an issue. If you own the image, then you can upload it to the board yourself.

I have converted them here and in the duplicate thread to normal links. Please bear this in mind in future posting

EDG
2009-Mar-10, 04:24 PM
Oh, sorry, didn't realise that I couldn't hotlink the pics.

aurora
2009-Mar-10, 06:10 PM
Well, something is unusual about Saturn. Maybe original events that formed the rings cleaned some mass out of the Saturn gravity well.

rommel543
2009-Mar-10, 08:04 PM
I read an article awhile ago regarding the disparity of the Saturn moons and the hypothisis that was raized was a possible collision between the moons. The author suggested that Saturn, like the other gas giants, had multiple similar sized moons but a collision between 2 or more of the moons (two collided and caused one to go off orbit and hit another) caused a single larger moon, along with the smaller moons plus the rings we see today.

Disinfo Agent
2009-Mar-10, 08:46 PM
That's certainly an interesting observation, especially in light of all the controversy surrounding the Titius-Bode Law (http://www.bautforum.com/astronomy/66784-there-pattern-how-our-solar-system-laid-out.html).

EDG
2009-Mar-10, 09:51 PM
That's certainly an interesting observation, especially in light of all the controversy surrounding the Titius-Bode Law (http://www.bautforum.com/astronomy/66784-there-pattern-how-our-solar-system-laid-out.html).

There's not much controversy about it - it's wrong. The only way you'd get regular patterns in orbits is because of the bodies evolving into orbital resonances due to tides and other gravitational interactions. But there's no reason whatsoever to believe that any other system would be laid out exactly like our own.

Getting back on the subject though - there are resonances in the saturnian system but they don't explain why there are so many small bodies. Though interestingly I saw a conference abstract (can't find the link now, but it was from before Voyager got to Saturn) that claimed that Titan may be a captured body. I don't think anyone's taken that idea seriously since then, but it certainly seems to be the odd man out in the system (or maybe it isn't, and all the small satellites are the anomalies?).

I guess the problem with the idea that Titan somehow retarded the formation of the other satellites to prevent them from getting so big is that the Jovian and Uranian systems don't seem to have had the same thing happen there (e.g. why didn't the growth of Ganymede stunt the growth of the other three Galileans?).

timb
2009-Mar-10, 10:35 PM
EDG_ I have locked the duplicate thread as you requested

However you hot linked several images in violation of the forum rules (http://www.bautforum.com/forum-rules-faqs-information/32864-rules-posting-board.html)




I have converted them here and in the duplicate thread to normal links. Please bear this in mind in future posting

That's certainly a radical interpretation of the rules and the world. So "try to avoid" is now an absolute prohibition and wikimedia.org is not a public site?

In answer to the OP, it's just a coincidence.

EDG
2009-Mar-11, 01:12 AM
In answer to the OP, it's just a coincidence.

I'm curious to know why you declare that it's a coincidence given that you've presented no evidence to support that. Unless you forgot to add that it was just your opinion that it was coincidence.

Disinfo Agent
2009-Mar-11, 09:25 AM
There's not much controversy about it - it's wrong. The only way you'd get regular patterns in orbits is because of the bodies evolving into orbital resonances due to tides and other gravitational interactions. But there's no reason whatsoever to believe that any other system would be laid out exactly like our own.Actually, there is some evidence (http://www.bautforum.com/against-mainstream/67011-bodes-law-extrasolar-planets.html)...

Gigabyte
2009-Mar-11, 01:14 PM
How interesting (http://en.wikipedia.org/wiki/Dermott%27s_law)

EDG
2009-Mar-11, 03:44 PM
Actually, there is some evidence (http://www.bautforum.com/against-mainstream/67011-bodes-law-extrasolar-planets.html)...

On the ATM board. Riiiight.

Disinfo Agent
2009-Mar-11, 03:51 PM
Right, what? The evidence is real, although its significance is open to debate.

EDG
2009-Mar-11, 04:09 PM
Maybe other systems have their own relationships between their orbits caused by resonances and so on, but it's not the Titius-Bode "law".

Either way neither the Titius-Bode 'law" nor Dermott's law have anything to do with the question in my OP, which was about the masses of the satellites.

01101001
2009-Mar-11, 06:21 PM
I have converted them here and in the duplicate thread to normal links.

Total guess, but would these larger images be easier to read?

Jovian moons (http://en.wikipedia.org/wiki/File:Masses_of_Jovian_moons.png)
Uranian moons (http://en.wikipedia.org/wiki/File:Masses_of_Uranian_moons.png)
Neptunian moons (http://en.wikipedia.org/wiki/File:Masses_of_Neptunian_moons.png)
Saturnian moons (http://en.wikipedia.org/wiki/File:Masses_of_Saturnian_moons.png)

Neverfly
2009-Mar-12, 12:20 AM
Or, looking at this:
http://upload.wikimedia.org/wikipedia/commons/6/67/Relative_satellite_sizes.jpg
One might wonder if the Pie charts are a bit misleading.

grant hutchison
2009-Mar-12, 12:36 AM
On the ATM board. Riiiight.And also published (http://fr.arxiv.org/abs/0803.2240) in Revista Mexicana de Astronomía y Astrofísica.
It's certainly a fine exercise in curve-fitting.

Grant Hutchison

EDG
2009-Mar-12, 12:58 AM
Or, looking at this:
http://upload.wikimedia.org/wikipedia/commons/6/67/Relative_satellite_sizes.jpg
One might wonder if the Pie charts are a bit misleading.

I'm not concerned about the mass/size distribution of satellites between the systems of the gas giants, I'm talking about the mass/size distribution of the satellites within each system. So the pie charts are entirely relevant and not misleading.

Neverfly
2009-Mar-12, 01:13 AM
I'm not concerned about the mass/size distribution of satellites between the systems of the gas giants, I'm talking about the mass/size distribution of the satellites within each system. So the pie charts are entirely relevant and not misleading.

That's exactly my point.
Try comparing them to eachother- and by their actual size- not on segregated groups in which one HUGE moon that dwarfs the rest may mislead you.

EDG
2009-Mar-12, 01:22 AM
That's exactly my point.
Try comparing them to eachother- and by their actual size- not on segregated groups in which one HUGE moon that dwarfs the rest may mislead you.

I think you're missing my point entirely, and I'm not asking about comparing them to eachother. The question is why Titan is so much more massive than the other major moons in the saturnian system, while the major Jovian and Uranian satellites are much more similar in mass to eachother. Comparing all the satellites with eachother doesn't contribute anything to answer that.

Those "segregated groups" are exactly what matters to me, because they represent the formation conditions around each gas giant. The formation of Uranus' moons didn't influence or affect the formation of Saturn's or Jupiter's, so why should it matter that Titan or Ganymede are bigger than they are?

Neverfly
2009-Mar-12, 01:32 AM
so why should it matter that Titan or Ganymede are bigger than they are?

I may be missing your point.

It was just a thought.

timb
2009-Mar-12, 09:57 PM
I'm curious to know why you declare that it's a coincidence given that you've presented no evidence to support that. Unless you forgot to add that it was just your opinion that it was coincidence.

Origin of Europa and the Galilean Satellites (http://arxiv.org/pdf/0812.4995v1)

parejkoj
2009-Mar-12, 10:35 PM
EDG: it's a good point. I'll see if I can get a friend who works on planetary formation to post.

qraal
2009-Mar-13, 10:14 AM
According to the Modern Laplacian Theory, developed by Dr. Andrew Prentice, Titan is a captured object from an originally Solar orbit. That's why Iapetus is so far out compared to the other mid-sized icy moons - it was slung out by the Titan capture process. Another moon might have actually collided with Titan during the process, perhaps surviving as Xanadu or some other "geologically" distinct feature on Titan's surface.

frankuitaalst
2009-Mar-13, 10:17 PM
Maybe this article can be an entry :
http://www.lpi.usra.edu/meetings/lpsc2005/pdf/2378.pdf

EDG
2009-Mar-15, 05:06 AM
Thanks frank, that article seems to go some way to answering the question.

timb
2009-Mar-15, 11:51 PM
Thanks frank, that article seems to go some way to answering the question.

The MLT is very much a minority theory.

Heathen
2009-Mar-17, 02:56 AM
timb wrote:

“The MLT is very much a minority theory.”

Yes. And I’m curious why Prentice thought that a Titan capture would be helped by this theory. A more detailed examination:

http://arxiv.org/ftp/astro-ph/papers/0602/0602512.pdf

EDG
2009-Mar-17, 03:41 AM
The MLT is very much a minority theory.

It's better than "it's a coincidence".

Maybe the details of the theory might not stand up to scrutiny (or maybe they do, I don't know), but I think having Titan be a captured body makes a lot of sense when you compare it to the other satellites. Look at the stats:

http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturniansatfact.html

Mass Radius Mean density Visual geometric albedo
(1020 kg) (km) (kg/m3)
Major Satellites
Mimas (SI) 0.379 209 x 196 x 191 1150 0.6
Enceladus (SII) 1.08 256 x 247 x 245 1610 1.0
Tethys (SIII) 6.18 536 x 528 x 526 960 0.8
Dione (SIV) 11.0 560 1470 0.7
Rhea (SV) 23.1 764 1230 0.7

Titan (SVI) 1,345.5 2,575 1880 0.22
Hyperion (SVII) 0.055 185 x 140 x 113 570 0.3
Iapetus (SVIII) 18.1 718 1090 0.05 / 0.5

Orbital Rotation
Semimajor axis Period* Period Inclination Eccentricity
(103 km) (Saturnian Radii) (days) (days) (degrees)
Major Satellites
Mimas (SI) 185.52 3.0783 0.9424218 S 1.53 0.0202
Enceladus (SII) 238.02 3.9494 1.370218 S 0.00 0.0045
Tethys (SIII) 294.66 4.8892 1.887802 S 1.86 0.0000
Dione (SIV) 377.40 6.2620 2.736915 S 0.02 0.0022
Rhea (SV) 527.04 8.7449 4.517500 S 0.35 0.0010

Titan (SVI) 1,221.83 20.273 15.945421 S 0.33 0.0292
Hyperion (SVII) 1,481.1 24.575 21.276609 C 0.43 0.1042
Iapetus (SVIII) 3,561.3 59.091 79.330183 S 14.72 0.0283

It seems pretty clear that in terms of size, the inner five major satellites are very similar. Then there's a big orbital gap, and then Titan which is much larger and more massive than the other moons, then there's chaotically tumbling Hyperion and then Iapetus which is similar in size and mass to the inner moons. I could well believe that Titan was captured by Saturn (IIRC it's eccentricity is still a bit anomalous), disrupted some moons beyond Rhea and possibly leading to the shattering of proto-Hyperion - Iapetus may well have formed out there and wasn't affected by Titan.

Also, I've been doing a bunch of satellite formation runs in gravity simulator and so far it seems that they tend to produce satellites of the same sort of size and mass, which further persuades me that it'd be very unusual to form one huge satellite and lots of relatively tiny ones.

timb
2009-Mar-17, 06:26 AM
It's better than "it's a coincidence".


I don't think so. Why is Mars so similar in color to Antares? couldn't be a coincidence could it. Any theory's better than that. Maybe they are both parts of the same object that broke up long ago.

Why don't you read the paper I linked to that gives an explanation in terms of the more widely accepted theory that the regular moons are the remains of the planetary accretion disk, and then tell us which one you think is better.

EDG
2009-Mar-17, 09:04 AM
I don't think so. Why is Mars so similar in color to Antares? couldn't be a coincidence could it. Any theory's better than that. Maybe they are both parts of the same object that broke up long ago.

Spurious argument. Just because two things are the same colour doesn't imply a common origin.

Why don't you explain why you think it's a coincidence, given that Titan's mass is so much greater than that of the other regular satellites in the same system? Can you explain why a similar situation doesn't occur at Jupiter and Uranus?



Why don't you read the paper I linked to that gives an explanation in terms of the more widely accepted theory that the regular moons are the remains of the planetary accretion disk, and then tell us which one you think is better.

It offers a possible explanation for Titan's size. I'm offering another. While I don't disagree that moons form in a regular accretion disk, but there's nothing really compelling to convince me that their specific scenario of events in the saturnian system is actually what happened there (maybe if they wrote a paper specifically on the formation of Titan and the saturnian satellites they might be more convincing, but a throwaway paragraph in a paper about Europa and the Galilean satellites isn't going to cut it). Maybe Titan wasn't captured either, I just don't see a reason to rule it out at this stage.

Almost all the simulation runs I've done so far produce moons of roughly equally size and mass (one run produced two large moons and one tiny satellite that was an original moonlet that hadn't got absorbed into the big moons). So far I've tried a base run with low eccentricity of the moonlets (three big moons formed), widening the range of eccentricity of the moonlets (two big moons plus one moonlet formed, in low eccentricity orbits), reducing their initial eccentricity to zero (three big moons with eccentric orbits formed), and widening the disk itself (four big moons formed). You can see them here: http://www.orbitsimulator.com/cgi-bin/yabb/YaBB.pl?num=1237164016

I suspect the only way I can naturally form one really big satellite and lots of little ones here is to have a denser belt of material at the distance that the really big satellite forms. But then one has to explain why that's there, which probably requires some really weird density distributions in the protosaturnian disk. Or, the alternative is that Titan is captured, and that there were originally 5-10 bodies around the same size/mass as the other Rhea, Dione, Iapetus etc in the system before it got there but that some got ejected or destroyed (and maybe Hyperion is what's left of one).

I don't think it's just random chance or coincidence that Titan is so much bigger though - it seems that something different happened in the Saturnian system that didn't happen in Jupiter's and Uranus'.

Heathen
2009-Mar-17, 06:09 PM
About 6 years ago I entertained the idea that Titan might be a captured proto-Centaur. I had assumed that such a capture would devastate the original satellite system, leading to a re-accretion of most of the original moons.

The disparity is compelling and begs explanation.

http://www2.jpl.nasa.gov/saturn/gif/ring_sat1.gif

A comparison of the mass of the largest secondary to the mass of the parent planet adds to the mystery:

Ganymede = 1/12,800 mass of Jupiter.

Titan = 1/4,225 mass of Saturn.

Oberon = 1/14,500 mass of Uranus.

Before I link to the 6 year old thread addressing this subject, a little clarification might be in order. A glitch took place upon the merge placing all of my pre-merge posts under a new name (Anonymous) but you can still tell that it’s me because the responses address me as Heathen.

The subject is first raised at the end of post # 17:

http://www.bautforum.com/against-mainstream/3798-moon-planet.html