Gas Giant satellite system limits

[Malenfant]

http://www.swri.org/9what/releases/2006/Canup.htm

This confirms something I've suspected for a while - the mass of the satellite system of gas giants are usually around a specific ratio of the mass of the primary. So it looks like you'd only be able to get earth-mass satellites forming around brown dwarfs...

If figure you'd need to have a 30-40 jupiter mass brown dwarf to be able to start getting satellites that are about the mass of Earth.

 

[Jame]

Now I know that any Earthlike (masswise) worlds around a Jupiter is artificial... Thanks.

 

[Border Reiver]

I had a glance at the Nature article. Although it's out of my field (euphamism for "I have no idea what they're talking about"), I am disturbed that the article uses so many approximations, best guesses, very nearlies and rough estimates within its syntax.

It's not like they're writing in New Scientist.

 

[Laryssa]

Originally posted by Malenfant:
http://www.swri.org/9what/releases/2006/Canup.htm

This confirms something I've suspected for a while - the mass of the satellite system of gas giants are usually around a specific ratio of the mass of the primary. So it looks like you'd only be able to get earth-mass satellites forming around brown dwarfs...

If figure you'd need to have a 30-40 jupiter mass brown dwarf to be able to start getting satellites that are about the mass of Earth.

Wasn't the Earth a rather unique case with regards to satellite formation though? The Moon was said to form through the Earth's collision with another planet, this caused the Earth to eject a mass out of its side.

What happens if one gas giant were to collide with another gas giant? The accretion theory of satellite formation seems to produce smaller satellites than a direct collision between two planets.

Also you have to consider binary star systems. Alpha Centauri A has 1.1 solar masses, and Alpha Centauri B has 0.89 solar masses in other words B has 80% of the mass of A, so if it can happen with stars, it can also happen with gas giants. Our Solar system has such a limited number of examples of gas giants, it can't account for all possibilities. Any Gas giant with an Earth-sized moon is most likely a binary planet. How would such a thing form? I think this way.

You have a normal Jupiter style satellite formation, and then an Earth-sized planet gets pulled in toward it, the Earth-sized planets then exchanges momentum with one of the gas giants natural satellites and ejects it from orbit around the gas giant causing the Earth-sized planet to be captured as a satellite of the gas giant.

 

[Malenfant]

Tom, this is science. I'm sure you can concoct any number of reasons why you think it could be wrong or how there could be exceptions, but I'm more inclined to assume the scientists are generally correct here.

This article isn't talking about terrestrial worlds, so those aren't relevant to the discussion. Stars are not planets so the same rules do not apply, and gas giant collisions are going to be so extremely rare anyway that those can effectively be ruled out. And if they do collide then it's more likely that you'll just have them merge with some debris thrown in orbit, but you're going to get weird configurations after that anyway - it's not the norm.

Capture *is* possible but not as likely as you might think, you need the bodies to be approaching eachother in specific ways for it to work instead of for one to be ejected completely.

 

[Fritz_Brown]

Well, Mal, I think he was asking about possibilities, not just probabilities. After all, we are working with Traveller worlds here....

 

[Malenfant]

Originally posted by Fritz88:
Well, Mal, I think he was asking about possibilities, not just probabilities. After all, we are working with Traveller worlds here....

Yeah, but what he was talking about isn't particularly possible. It's just funny that we say "here's what science says is likely" and then people immediately start trying to think of exceptions that work differently. Maybe it's because the worldgen in Traveller requires that you have to come up with loads of exceptions to get the impossible planets to work, but that's not how the real universe works at all.

I mean, really I posted the link here because I figured that the people who are interested a realistic Traveller universe would want to read it and possibly incorporate that info into their universes. It's got pretty much no relevance at all for people who aren't interested in a realistic TU, and they can carry on doing whatever they like and ignore it .

 

[Laryssa]

The Earth was not the usual case. How many Earth-size planets have moons that more properly belong to gas giants, not to terrestrial worlds. Earth's moon would more properly belong to a gas giant. The norm would be for Earth-sized planets to have asteroid sized moons.

 

[aramis]

Recent article in Astronomy poiints out that Charon is likely the result of just such an unlikely event; pluto got smacked and tossed out several satellites, of which Charon is the largest.

Mal:

What science says is likely is often presented as factual, rather than as a WAG. Just like we know about how much energy should be released in a nova event, but we don't know exactly where we'd be safe from it.

We are not even certain about the number of moons of the gas giants, and a sample of 9 isn't statistically reliable anyway, let alone the 4 gas/ice giants in our system.

Now, until the TPF, we're not going to be able to get good data in sufficient points to make valid statistical analyses.

Oh, wait, didn't TPF just get cancelled?

 

[Fritz_Brown]

Mal, the guy in me who wants non-boring settings wants to know what's normal AND what's possible. And, TY for posting articles like this.

 

[Malenfant]

Originally posted by Aramis:
Recent article in Astronomy poiints out that Charon is likely the result of just such an unlikely event; pluto got smacked and tossed out several satellites, of which Charon is the largest.

And that has nothing to do with anything here at all. This article is not talking about terrestrial planets! This article is about the formation of gas giant satellite systems only - references to Earth's moon or Pluto's moon are completely irrelevant here, because they are not formed in the same way as gas giant systems.

What science says is likely is often presented as factual, rather than as a WAG.

That's because it isn't a "WAG" (Wild Ass Guess) at all. Scientfic models are based on observation and experimentation and available data, and this is no exception. Sure, we may not have 100% of the data that can be acquired but but that certainly doesn't mean that we're just making wild guesses and it also doesn't mean that you should assume that the science is wrong either. Yes, science can change over time as new data is acquired but that's how it's supposed to work - our understanding changes as we acquire new data. But that doesn't even remotely mean that what we know currently is just a "wild ass guess".

Honestly, sometimes I wonder if people have a clue about how science really works here...

Just like we know about how much energy should be released in a nova event, but we don't know exactly where we'd be safe from it.

There's a huge difference between saying "OK, the uncertainties mean we don't know exactly where we'd be safe from a supernova" and saying "here are the numbers run in this model but we're going to assume they're wrong because they're inconvenient".

We are not even certain about the number of moons of the gas giants, and a sample of 9 isn't statistically reliable anyway, let alone the 4 gas/ice giants in our system.

Yes, but this has nothing to do with the number of gas giants we know of. These are models run using generic planetary accretion theories. They're not based on specific gas giants. This is what happens when we put our current knowledge of physics together with the computing power available to us to run models of satellite systems.

(Besides, the number of moons a gas giant has is irrelevant. We know all the major ones, and all the tiny ones have no real contribution to the total mass of the system).

Now, until the TPF, we're not going to be able to get good data in sufficient points to make valid statistical analyses.[/qb]

Who said this was a statistical analysis though? It's a model based on well known and well understood theories of planetary formation. It produces results that closely match the gas giants that we know of. That being the case we can be pretty confident that the model works.

I just wish people would stop trying to find excuses to show that scientists are wrong, particularly when they don't even understand how the models are generated in the first place (or even the scientific process, it seems). If you have good reason to believe that they're wrong, then run your alternate models and publish them in a scientific paper to show that. But otherwise, either take it as it is or ignore it.

 

[Laryssa]

Originally posted by Malenfant:
</font><blockquote>quote:</font><hr />Originally posted by Aramis:
Recent article in Astronomy poiints out that Charon is likely the result of just such an unlikely event; pluto got smacked and tossed out several satellites, of which Charon is the largest.

And that has nothing to do with anything here at all. This article is not talking about terrestrial planets! This article is about the formation of gas giant satellite systems only - references to Earth's moon or Pluto's moon are completely irrelevant here, because they are not formed in the same way as gas giant systems. </font>[/QUOTE]Jupiter has 318 times the mass of Earth.
ARE YOU SAYING THAT A TERRESTRIAL PLANET WITH THAT SAME MASS WOULD HAVE LARGER MOONS? How are the moons supposed to know what kind of planet they are orbiting? Gravity is gravity, it doesn't matter whether is is a gas giant that is producing that gravity or a terrestrial planet. The Universe has a habit of not listening to what a scientist has to say, no matter how important he may be. All we really have to go by are the gas giants in our own Solar System. In our own Solar System for instance we made the observation that the 4 gas giants are outer planets, it was therefore judged that gas giants form far way from the Sun and a general rule was assumed that there would be no gas giants close to their primary, because we've seen none in our own Solar System. Then people started detecting gas giants orbiting close to stars, important scientists said this couldn't happen and that their computer models didn't allow for that, but the Universe didn't listen, it did what it pleased.

Now just because some prominent scientist's computer model shows something doesn't mean we should automatically accept it as fact. What we have to do is actuallu observe extra-Solar gas giants and see how big their satellites are, and we must make observations of many many gas giants to come up with any valid conclusions. $ gas giants simply aren't enough to establish some kind of rule on gas giant system formation.

Originally posted by Malenfant:
</font><blockquote>quote:</font><hr />What science says is likely is often presented as factual, rather than as a WAG.

That's because it isn't a "WAG" (Wild Ass Guess) at all. Scientfic models are based on observation and experimentation and available data, and this is no exception. Sure, we may not have 100% of the data that can be acquired but but that certainly doesn't mean that we're just making wild guesses and it also doesn't mean that you should assume that the science is wrong either. Yes, science can change over time as new data is acquired but that's how it's supposed to work - our understanding changes as we acquire new data. But that doesn't even remotely mean that what we know currently is just a "wild ass guess".</font>[/QUOTE]Though I think it is better to look through a telescope than at a computer model, the best way to learn about the Universe is to look at it. The Universe doesn't always agree with out computer model, and when it doesn't that usually means there is something wrong with the computer model and it must be changed. There have been many computer models of how the universe formed, they created those computer models based on observational data up to that point, and then later observations revealed some inconsistencies with that computer model.

I think their is more than one way to create a gas giant, and their is more than one way to create a gas giant satellite system. Not all gas giants are made in the same factory.

What happens when you have a gas cloud collapse and their is not enough gas to make a star? You get a brown dwarf of a gas giant, I'm not sure what the difference between the two is. A brown dwarf will generally have planets and a gas giant will have satellites, but the difference is one of semantics. is their really a lower limit to how much mass a brown dwarf must have. A gas giant can certainly form in the middle of interstellar space instead as part of a Solar System for instance, and then be captured by a passing star rather than being formed out of the same cloud the star was formed out of.

Originally posted by Malenfant:
Honestly, sometimes I wonder if people have a clue about how science really works here...

Yep, if the scientist is really important and he says something, then the Universe must listen to him and do what he says.

 

[Malenfant]

Tom, either learn some basic science or get some basic reading comprehension. You have no idea what you're talking about.

The universe doesn't work on belief or opinion. We gather data, we formulate models, if those models don't tally with observations then we discard the model. What gets published is the stuff that DOES tally with what is observed.

And like I said, as we collect more data then theories get revised and updated. Continuing to scream about how stupid scientists were for saying that gas giants don't form close to stars is pointless - big deal, we got new data, we changed our theories to explain those while still working for everything else, we carried on, end of subject. THIS IS HOW SCIENCE WORKS! IT IS NOT CONSTANT AND UNCHANGING!

I'm telling you that we know that moons of terrestrial planets do not form in the same way as moons of gas giants. You're just blithely continuing on with hands over your eyes/ears ignoring all that because... well, I have no idea why you refuse to accept it to be honest.

Your opinions on the subject do not change the facts and do not change the models derived from those facts. If you have reason to believe differently, then make your own scientfic observations and formulate your own models and publish your own paper refuting the existing models in a scientific journal. Otherwise, stop trying to make out that you know better when you don't.

 

[Laryssa]

Its not my job to prove that large satellites of gas giants can happen, its your to prove that they can't, you the one making the more extraordinary claim, not I. if we look at astronomy we see many examples of objects whose satellites are a large portion of the primary's mass. Alpha Centauri A and B are one such example, they are stars made out of gas, and gas giants are made out of gas too. It takes more than citing a computer model I've never seen to convince me otherwise.

 

[Malenfant]

Originally posted by Laryssa:
Its not my job to prove that large satellites of gas giants can happen, its your to prove that they can't, you the one making the more extraordinary claim, not I. if we look at astronomy we see many examples of objects whose satellites are a large portion of the primary's mass. Alpha Centauri A and B are one such example, they are stars made out of gas, and gas giants are made out of gas too. It takes more than citing a computer model I've never seen to convince me otherwise.

Again, you show your usual ignorance of how science works.

First, actually the onus is on you to demonstrate how the model is incorrect if you're going to criticise it. So far all you've done is say "I don't believe it", which is not proof - and you're the one making the extraordinary claim that is based on ignorance.

Second, have you even read the article? As usual your reading comprehension is abysmal - despite being told several times, it still hasn't clicked with you that they're talking about gas giants and not terrestrials or stars. That said I seem to recall that it is a standard tactic of yours to ignore what is said. You seem to be pathologically incapable of recognising when to listen to people and recognise that they know more about a subject than you do and that therefore you should listen and learn from them. Though really I think you're just trolling.

Third, you can't prove a negative.

Fourth, I'm not the one making the claim - if you have that much of a problem with it then take it up with the author of the paper.

Finally, you can disbelieve it if you like. But don't pretend that you're right or that you know any better if you do that, because you're not.


Honestly, are we going to get this kind of ignorance and hostility towards knowledge every time we post science links here? If some people here would prefer to wallow in their ignorance then I'd much rather that they just shut up and didn't comment here.

 

[Laryssa]

Look I agree that large moons of gas giants seem unlikely given what we know about the 4 gas giants in out Solar System, but that's as far as I'm willing to go with that. Your saying that their impossible. There is a huge difference between impossible and unlikely. There are trillions of stars out their, and just about every star we see in the night sky was unlikely to occur, as most of them have a mass greater than the Sun and are much brighter, most stars aren't like those we see in the night sky, the most likely kind of star is the red dwarf, the kind that is mostly too dim to see without a telescope.

As you say, its impossible to prove a negative, I was never saying that Earth-sized moons of gas giants were common, I was merely saying that they could occur, and that so far I've seen no evidence that they couldn't. A computer model is not the real world, and I'd go with the real world every time. I doubt a computer model can prove a negative.

Also there is the evidence of terrestrial planets in our Solar System and the evidence of multiple star systems that are light years away. What's in between a terrestrial planet and a star? Gas Giants for one.

If something can happen with Terrestrial planets and something can happen with stars, one would ordinarily think that it might also happen with the middle ground between terrestrial planets and stars. I hear it takes only 80 jupiters to make a star, so if you put two 50 Jupiter gas giants together you get a star. Gas giants and stars are made of the same stuff, so what happens with one might also happen with the other. All it waits for is for a sensitive enough telescope to detect two gas giants orbiting each other as they orbit around a star. Because if a gas giant can have another gas giant as a satellite, it might also have an Earth-sized moon.

 

[Malenfant]

I'm not saying they're impossible at all. Again, read what is said.

You keep bringing things up that are totally irrelevant to the matter at hand. Star types are irrelevant. Terrestrial worlds are irrelevant. All we're talking about here are satellite systems of gas giants.

Seeing no evidence for something is no reason whatsoever to believe that it can exist. Computer models are based on the real world, and given that we've never seen earth-mass satellites around Jupiter-mass or less gas giants I'm inclined to go with the computer models that say that outcome should be expected. The models fit the observations - your assertions do not, and aren't even *based* on observations or evidence.

Your logic is designed to make sense to you only, Tom - it's quite baffling to anyone else. You claim that it's possible to have a gas giant orbiting a gas giant and then claim that if that's possible then it can have an earth-sized moon - but you don't even have evidence that it's possible for a gas giant to orbit another one in the first place. Perhaps it is possible for that to happen, but that's a very abnormal situation, and there's certainly no guarantee if that did happen that it's suddenly magically possible for them to have earth-mass satellites.

Instead of making the wrong extrapolations based on your ignorance, why don't you actually take the time to read up and learn about the subject? Gas giants are not terrestrial planets and they are not stars - they form differently and so do their satellites, and that is what this paper is about. Accept that and maybe we might get somewhere, because your opinion certainly isn't based on fact, but their models are.

 

[mike wightman]

[MODERATOR HAT ON]
Let's move the discussion forward now please.

This thread is now being watched - so let's not have a reason to lock an interesting topic.

 

[Plankowner]

So, if we use the 0.1% limit for satellite mass for GG's as the report suggests for ALMOST every GG we want to develope, then as part of your planetary development, you are going to HAVE to calculate the mass of your GG and all of it's moons.

I would argue that the rings and the size S moons could probably be ignored, but all the size 1 and larger moons will have to have their mass calculated so that you can see if they are even allowed. I would suggest a modification to LBB6 (or just about any other design system, since they seem to be based on LBB6) as follows:

1) When you roll the GG, immediately determine it's size (50% each per LBB6) and roll it's size and mass.

2) Roll the number of moons normally. Roll the size of the moons, but put an upper limit of Size 3. If you roll greater than Size 3 for a moon, make is Size S. Calculate mass per LBB6 for each moon Size 1+.

3) If the total mass of the moons is less than 0.1% of the GG mass, leave as is. If greater, then reduce the size 3 worlds to size 2, then reduce the size 2 worlds to size 1 and finally reduce the size 1 worlds to size S until total mass is under 0.1% of the GG mass.

This would tend to give you several worlds that are all in the same size classification, which matches what we see at Jupiter, 4 worlds about the same size (approximately) and lots of size S worlds.

WHADAYA Think?

 

[Malenfant]

Something like that would work (isn't it 0.01% of the mass though?). I don't think you need to calculate masses but generally just say for Jupiter-mass objects (LGGs or the larger SGGs) the maximum size is 3, and for Uranus/Neptune mass objects (the smaller SGGs) the maximum size is 1 or 2. Brown Dwarfs can have larger satellites though - a 40 MJ Brown Dwarf could have an earth-mass satellite or two.