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Current depictions of the Birrin world show it with two moons, one large and one small. However current research I can find suggests multiple moons around an earth sized planet are inherently unstable.

Does anyone have any knowledge of a way a multiple moon system could work?

If not, I will be reducing the Birrin world to a single-moon planet like earth.
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:icongatemonger:
gatemonger Featured By Owner Jan 16, 2014
Is it possible for a moon to have its own satellite?
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:iconabiogenisis:
Abiogenisis Featured By Owner Jan 17, 2014
It seems that it only can for a while, before it becomes tidally locked and simply crashes into the bigger moon.
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:icondanirevan:
DaniRevan Featured By Owner Jan 13, 2014
I didn't realize multimoons around a Earth-sized world were unstable...

Wait...does this apply possibly to super-Earths too? Or just "earth sized"?

Because this may not be plausible anymore: danirevan.deviantart.com/art/2…
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:iconabiogenisis:
Abiogenisis Featured By Owner Jan 17, 2014
Yeah I am thinking that super earths might be able to carry other possible configurations for longer, though I dont think anyone truly knows for sure.

My research indicated that your system would be unstable, but the moon may stay there for many years before crashing into the moon or the planet, since there is now a theory earth had two moons for a time before they combined.
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:icondanirevan:
DaniRevan Featured By Owner Jan 17, 2014
Thank you for your insight.

The moons, I forgot to mention earlier, are in 2:1 resonance. Would that stabilize them, or is it just impossible?
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:iconabiogenisis:
Abiogenisis Featured By Owner Jan 19, 2014
Sadly I just dont have the expertise, so I decided to err on the side of caution. I think the problem is the resonance isnt clean, because of the sun and other planet's influence.
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:icondanirevan:
DaniRevan Featured By Owner Jan 19, 2014
Sorry about a 3rd post, but then that would mean the Jovian moon resonance isn't clean either? Or is there a factor that keeps them in a stable resonance?
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:iconabiogenisis:
Abiogenisis Featured By Owner Jan 20, 2014
The moons around Jupiter I believe are kept in place because of the sheer mass of the planet.
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:iconfeaturelessmask:
FeaturelessMask Featured By Owner Jan 9, 2014
I know this comes to late but there pare some cool physicists who hang out on /r/worldbuilding.
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:iconblazr-san:
BLAZR-SAN Featured By Owner Jan 8, 2014
Two words Abio': Orbital Resonance; look it up online and study it attentively - it's a bit complex when you get down to it, but you'll get the whole concept. Just think of the Galilean moons, Pluto or Neptune, and so on; you should know these spheres (and their satellites) I would believe.

From there, scale them, give them life forms, sufficient gases needed to support life, sustainable atmospheric layers, and unique-but-realistically-based functions and voila! Nascent moons for the Birrin Sphere!!
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:iconabiogenisis:
Abiogenisis Featured By Owner Jan 9, 2014
Are you suggesting the idea of making the birrin world a gas giant moon?
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:iconblazr-san:
BLAZR-SAN Featured By Owner Jan 15, 2014
No, but using orbital resonance in a non gas giant system is a creative way may to make a theory breaker, right?

that's the main reason why I suggested it... It mayyyyyy take time to amend the orbital resonance theory to fir the theme, but it could be done with some effort and devotion I suppose...

give it a shot! :icongrin--plz:

BTW - note that I mentioned Pluto (despite it not being a planet, it has some sort of orbital resonance phenomenon relating to it... I think... I need to reread the orbital resonance theory once more just to be sure it falls into the category..... but still, try the idea out -- and, by god, KEEP BIRRIN FROM BEING A GAS GIANT AT ALL COSTS. Keep to its current specs and you'll be okay.)
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:iconabiogenisis:
Abiogenisis Featured By Owner Jan 17, 2014
Problem is I am SO poor at maths I cant run those sort of simulations :P
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:iconblazr-san:
BLAZR-SAN Featured By Owner Feb 5, 2014
hmmm. well then stick to one moon. problem solved... sorta......

Oh well!!
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:iconabiogenisis:
Abiogenisis Featured By Owner Feb 8, 2014
OR a Super Earth that the birrin world orbits. Another avenue to explore.
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:iconblazr-san:
BLAZR-SAN Featured By Owner Feb 10, 2014
Oooooooooh, that may work rather well actually!

give that a shot, and see what more will come out of it!

I can't wait to see what the bigger planet will be like!!

^__________________^
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:iconfmilluminati:
fmilluminati Featured By Owner Jan 7, 2014  Hobbyist Digital Artist
A multiple moon system is inherently unstable if it formed as the result of a giant impact.  If the moons are captures they could be stable.  The problem is, smaller bodies like the Earth don't have enough gravity to make capturing a moon sized object likely, nevermind two of them.  This is because the cone of approach angles that would result in a capture is so small it's far more likely that a moon sized object would simply fly by an earth sized planet or crash into it.  So yes, you could have a stable two moon system by capture, but capture is so incredibly unlikely and difficult it would probably never happen for EVEN one moon.  

If Birrin is going to be plausible, it's going to need no more than one moon.  Then again, anything could happen in another solar system. :)
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:iconabiogenisis:
Abiogenisis Featured By Owner Jan 9, 2014
Its true, I am going to reduce the birrin world to a single moon.
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:iconobsidiangrey:
ObsidianGrey Featured By Owner Jan 6, 2014  Hobbyist General Artist
Our planet earth has an abnormally large moon for its size. Mars does have two moons but they're more like large meteoroids.
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:icongeekhyena:
Geekhyena Featured By Owner Jan 5, 2014
I think Stanley Schmidt and  Ben Bova covered such systems in Aliens and Alien Societies (my copy is in storage or I'd look). Amazon has it for cheap.  
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:iconparasky:
Parasky Featured By Owner Jan 5, 2014  Hobbyist Digital Artist
Have you considered having one larger moon like Earth's and another moon that is just a captured asteroid of decent size that orbits the large moon? Or perhaps two captured asteroids like the two moons of Mars?
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:iconabiogenisis:
Abiogenisis Featured By Owner Jan 9, 2014
I did consider that, though since they would be so small they would be barely visible in paintings and so there is no real point to include them.
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:iconthe-ska-king:
The-SKA-King Featured By Owner Jan 5, 2014
I'm kind of on a run and can't read all the replies, but perhaps you could make it more of a three-planet dance. All three take up the same orbit and in that, orbit around each other. I don't know if there is any research or theories on this idea. And, honestly, the universe has awesome ways of making this work without them making much sense (until we're able to really look at it). As others have said, research right now is really sketchy and mostly reduced to mathematics and theory. Just do what you thing sounds like it'll work.
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:iconabiogenisis:
Abiogenisis Featured By Owner Jan 9, 2014
Most of the problems I found with multiple planet systems is that they all lock to one another, and in doing so reduce their rates of rotation, weakening their dynamo driven magnetic fields.
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:iconthe-ska-king:
The-SKA-King Featured By Owner Jan 10, 2014
Makes sense. If you thought about it, perhaps, the planet that you present is actually a moon orbiting a gas super giant. The radiation produced by the super giant is able to give a necessary heat to actually create the Kiln as the Birrin destroyed the equator. As far as you could spin it, the pictures drawn and presented just so happen to not have the Shepard in view. The sun, too, could be a massive one at that, if the planetary radiation bit doesn't stick with you. The other "moons" are actually just that. Moons.
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:iconabiogenisis:
Abiogenisis Featured By Owner Jan 11, 2014
The problem I found was that a moon needed to be wrapped in the gas giants own magnetic field to be defended against radiation, which from a massive star would be even higher. High mass stars also tend to have life spans too short to evolve complex life.
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:iconthe-ska-king:
The-SKA-King Featured By Owner Jan 11, 2014
Hmm... This is a tricky one. I'll probably have to look around at some of the stuff that pertains to this and get back to you. A more work intensive way to fix your problem is to go over the work you've already done and correct what is wrong. Or, from the point on, correct the size of them and refuse to acknowledge that you made a mistake at all, which would be easier.
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:iconabiogenisis:
Abiogenisis Featured By Owner Jan 17, 2014
Actually I will leave them as they are, and if any of them get published I will make the change before print :)
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:iconthe-ska-king:
The-SKA-King Featured By Owner Jan 17, 2014
Good plan. :D
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:iconurulai:
Urulai Featured By Owner Jan 5, 2014  Hobbyist General Artist
I've dealt with this myself and found a few solutions.  Though the easiest one I can suggest comes from Orbital Resonance.  Take a look at Pluto and Neptune or the Galilean Moons for good examples then just scale it.  I used Pluto and Neptune myself.
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:iconloone-wolf:
Loone-Wolf Featured By Owner Jan 5, 2014  Professional General Artist
didn't some planets in our solar system have more than one moon? I think neptune has more than 17 moons if i recall correctly... but that is a gaseous planet, couldn't really think a solid planet with multiple moons. found this article, if you hadn't already read it: content.time.com/time/health/a…
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:iconabiogenisis:
Abiogenisis Featured By Owner Jan 9, 2014
The problem seems to be related to mass, and a planet the size of earth simply cant hold on to multiple large moons for a long period of time.
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:iconloone-wolf:
Loone-Wolf Featured By Owner Jan 9, 2014  Professional General Artist
Hmm, yes, perhaps the planet needs to be big enough to hold more than one moons. The solution might be the size of the planet itself, i'm not very sure about this but maybe if we double the Earth's size, it would hold to two Moons of the same size as ours now.
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:icondarth-biomech:
darth-biomech Featured By Owner Jan 5, 2014  Professional Digital Artist
Some time ago it was thought impossible to binary stars have planets AT ALL. That is, until one such system was found... Space is big and mostly unexplored. God knows what could be there, and I don't think that multiple moons on stable trajectories is such far fetched thing.
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:iconabiogenisis:
Abiogenisis Featured By Owner Jan 9, 2014
Its true, though the birrin system I want to base only on known science.
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:iconred-fathom:
Red-Fathom Featured By Owner Jan 5, 2014
and our moon is? curious.astro.cornell.edu/ques…

instability is only a factor in the larger time frame. probly could have a small close moon, and a larger distant moon. would make crazy tides.
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:iconklausteufel:
KlausTeufel Featured By Owner Jan 4, 2014
I think the depictions can only be explained plausibly if Birrin's World and the smaller moon also orbit the larger 'moon', the latter being apparently a very larger 'super-earth'. We know massive solid planets exist. Because in "Kaybor-Kendi 'Tallantelli' Launch vehicle" you show the smaller moon coming between the larger body and Birrin's World, but in Seafarers it's smaller and probably further away.

Birrin's World also appears to have lower gravity than Earth, based on the Birrin's leg structure. So a 6Em body being orbited by say a 0.5 Em world (Birren's World) and another, perhaps smaller body might work.
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:iconmrquicksilver1:
MrQuicksilver1 Featured By Owner Jan 4, 2014  Student Traditional Artist
the only way jupiter has so many is a massive sphere of influence that allows them to be so far apart that they don't effect each other
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:iconfarunderheaven:
farunderheaven Featured By Owner Jan 4, 2014
Just a few years ago scientists discovered that a binary star system can support planets, maybe you could use the excuse that we haven't figured out yet how a dual-moon system would work?
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:iconrobomarkov:
Robomarkov Featured By Owner Jan 4, 2014
Multiple celestial bodies makes for serious problems if they are of substantial size. The main issue is that of tides. Next issue is that of plate tectonics. Having an extra moon would almost certainly increase the vulcanism of the Birrin homeworld. However, this could be mitigated by making one or both moons VERY small. Mars is a good example of multiple small moons.

However, keep in mind that Mars is dead and can never support life - it has no magnetosphere. Perhaps if it had a large moon then the swirling magma that creates the planetary magnetic field would not have stabilized and de-Gaussed itself.
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:icondurgaaz:
Durgaaz Featured By Owner Jan 4, 2014  Hobbyist Writer
It could be an unstable situation, you could have one moon (somewhere down the road timeline-wise) either leave orbit (Decayed, whether impacting the planet or sailing off into the void to be alone and planet-less forever), or impact with the other moon. It could make for some interesting plot in the species learning of the instability and trying to correct it, either in the past (if post-apocalyptic) or sometime in the future. It could provide impetus for a space-race so to speak!

Or if they are spacefaring, they could theoretically make an artificially stable 2-moon system. (Orbit managing thrusters on the moon, or something.)
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:iconterranabassador:
TerranAbassador Featured By Owner Jan 4, 2014  Student Digital Artist
I would suggest making Birrin a double planet with a single moon. If the larger current satellite is massive enough, the barycenter would be out in space, rather than inside Birrin istelf. You could then have the smaller current satellite orbit THAT. It should be a system pretty close to Pluto/Charon, which has the two in the center, orbiting the center of mass, which is then orbited by Styx, Nix, Kerberos, and Hydra.

I made a render blocking it out:

imgur.com/kCjFpPJ.jpg

The red dot would be the barycenter of the system, with everything orbiting that.
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:iconirg555:
irg555 Featured By Owner Jan 4, 2014
Doesn't Mars have two moons? Granted their tiny little things but shows the possibility exists. If not:

Can the two moons be on the same orbital track but in different positions where they're not attracting each other, like on opposite sides. Highly unlikely occurrence but the universe is big.

How about if the smaller moon orbits the larger moon and both or on the an orbital path around the planet? Is that any more stable?

With if the two moons are on very different orbital tracks where they wouldn't effect each other? Then it could be that the smaller moon isn't actually smaller but much further out?
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:iconbabakosen:
BabakoSen Featured By Owner Jan 4, 2014  Hobbyist Traditional Artist
Multiple moons are most stable around giant planets. Some giants, of order 5-10 Jupiter-masses, could support up to 10 Earth-masses in satellites in the habitable zone of a sunlike star. Case in point: HD 28185 b, a jovian planet on a 383-day orbit around a star that is nearly identical in mass and luminosity to Sol, It's the poster child for a planet that could host habitable exomoons (which is why it's the setting for my OC aliens).
Of course, this configuration can add a layer of two of complexity to the calendar and seasons.
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:iconhop41:
Hop41 Featured By Owner Jan 7, 2014
One my favorite settings. In our solar system trip times between planets can be months or years. Hohmann luanch windows can be years apart. Such a slow place prevents paced Flash Gordon type stories. But with a gas giant with several habitable moons, trip times are shorter and launch windows more frequent. Thus you can have a fast paced story set on several worlds without wildly implausible physics. I described such a system at hopsblog-hop.blogspot.com/2013…
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:iconeridanielsu:
eridanielsu Featured By Owner Jan 4, 2014  Student Writer
I'm not an astrophysicist, but what if they were in one of those orbital resonance things, like Jupiter's moons Io, Europa, and Ganymede. Would that solve the problem?
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:iconwetdryvac:
wetdryvac Featured By Owner Jan 4, 2014
There are some cases of three + body systems where at least one of the moons is fairly large relative to the primary body. Pluto, Charon + small bodies is a decent example:

mnrasl.oxfordjournals.org/cont…

For addressing this mathematically and via simulation in a more specific sense: www.orbitsimulator.com/gravity…
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:iconhop41:
Hop41 Featured By Owner Jan 7, 2014
Being so far from the sun, Pluto has a huge sphere of influence. The sun-pluto L1 and L2 are almost 8 billion kilometers from Pluto. And Charon is only about 18 thousand kilometers from Pluto. Lots of rooms for the outer moons to remain within Pluto's sphere of influence without being perturbed by Charon.

In contrast the sun-earth L1 and L2 are 1.5 million kilometers from earth and our moon is 384 thousand miles from earth. The moon will be a very disruptive influence to most objects within the earth's sphere of influence.

Lower orbits are fairly stable though. For example Geosynchronous Earth Orbits (GEO) (about 42,000 km from earth's center) suffer little disturbance from the moon. I believe a few Deimos or Phobos sized rocks could orbit earth at GEO altitude or a little higher or lower.
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:iconwyzilla:
Wyzilla Featured By Owner Jan 4, 2014
You could always do something similar to Pluto and Charon and skip the planet altogether. Two planetoids with one orbiting the other.
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:iconavancna:
avancna Featured By Owner Jan 4, 2014  Hobbyist Traditional Artist
But then Birrin would not be inhabitable, as Pluto is not large enough to have an atmosphere (that can support life)
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