# life on a large and strange world.



## Logos&Eidos (Feb 13, 2015)

While this is a World-building related question, I'm posting it here because in order to avoid unassery use of handwavium and get an understanding of logical implications of the ideas that i'm  playing around with.

A setting that I am considering for my science-fantasy is a planet roughly the size of Jupiter.  like Jupiter it has many moons, some of which are going to be habitable. Why a giant planet?  Because I wanted the endless expanse feel of world hoping space opera without the heache of interstellar civilizations. And so that no matter how far civilization seemed to progress  their would always be untamble wilderness; adding kaiju to the ecology also helps with that.

A planet the size of a gas-giant being perfectly habitable by human life is my  likely greastst usage of handwavium; the planet is problably going to be a construct of some kind,perhaps even the last bastion of sapiant life.

The planet isn't just massive it's also quite  exotic. Rocky Points and the plateaus that the natives call home, rise out of a dense and toxic sea of heavy gases, thought flow from the core of the world. 

My questions are.

What impact would the planets size have on it's weather and seasons.

How would having many moons effect the tides.


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## CupofJoe (Feb 14, 2015)

Multiple moons will probably mean a wider range of tides in the oceans. Most of the time the effects of the moons will cancel each other out or interfere with the flows but once in a while there will be an alignment that causes massive "Spring Tides". I don't know if the effects would be a great as they would on a planet like Earth as the oceans around us have had millions of years to get in-to-the-rhythm of one moon...
I'm tempted to say [with no evidence or knowledge] that weather will be more extreme. There would be a lot more "air" to get moving and therefore a lot more energy involved.
Season will depend on the shape of the planet's orbit and axial tilt...
[I can remember a SF story from years ago about gas miners finding life in the gasses of Jupiter. They had to fight 1000mph winds of corrosive acid as well as gas-whale creatures that were 20 miles long...]
One thing I'd mention... Dyson sphere... Not exactly what you are talking about...


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## Terry Greer (Feb 14, 2015)

Tides do depend on the size and distance of the moons. Earth is particularly unusual in the size of it's moon relative to its own mass.
But tides don't need to just affect the oceans - they'd have an impact on atmosphere as well - especially dense air. Fogs and mist from the depths could be synchronized with the moons - and they would be your tides. If the atmosphere is toxic at those times - that would be interesting.

Cup of Joe is right in that multiple moons would probably smear out any tidal effects, although you could get around this to some extent by having the moon orbits in harmonic resonant frequencies - something that tends to happen. But the tides can be detected even in the larger lakes. The force of the tides on earth is more a matter of ocean currents and coastal regions funnelling water movement.  E.g. in the med the average tidal range is less than 2 feet and there are several places where no range is visible at all. Most of these currents are set in motion by heat exchange and not by the moon at all. 
If the moon vanished the biggest effect would probabaly be on plate tectonics - I've even read some theories that think that it's the moons actions that have kept the surface of the earth cracked and flexible for so long leading to life on earth - though this isn't accepted yet.

Orbital resonance - Wikipedia, the free encyclopedia
That would make for a series of periodic 'high tide' when the moon positions were fully synchronised (which could be quite rare) .

It's worth saying that despite Jupiter's size the gravity on it is only 2.5 times that of earth - so it's eminently livable. If the world was poor in heavy metals (such as no iron/nickel core) you could probably get a larger world and keep the gravity at the expense of tectonic movement and vulcanism. That does bring potential issues as to  the world not having a mechanism for renewing its surface - but it could be a dying world where life still clings precariously - or one originally partially constructed as you say (perhaps as general 'sweepings' from the solar system - consisting mainly of lighter elements - by an intelligence tidying up!.  

It might also be worth looking at Jack Vances Big Planet - Big Planet - Wikipedia, the free encyclopedia which  is a metal-poor worls (which presumably reduces the mass and lets it attain a larger size.


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## Hainted (Feb 14, 2015)

If you really want the endless world hopping expanse of a space opera without the headache of interstellar travel than I wouldn't make the giant planet livable, I would make the moons livable. As long as the giant itself sits in the habitable zone multiple moons would be capable of supporting life. Imagine one moon with an erratic orbit, home to a warlike race that attacks whatever other moon they come near before retreating. Hmmmm?

But to get back to the original question, Reddit's Astrophysics forum helped me out a lot when I was designing my binary planet system for a story, and several physics forums around the net have sections dedicated to writers posing questions to help make their stories more plausible.


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## Logos&Eidos (Feb 14, 2015)

CupofJoe said:


> Multiple moons will probably mean a wider range of tides in the oceans. Most of the time the effects of the moons will cancel each other out or interfere with the flows but once in a while there will be an alignment that causes massive "Spring Tides". I don't know if the effects would be a great as they would on a planet like Earth as the oceans around us have had millions of years to get in-to-the-rhythm of one moon...
> I'm tempted to say [with no evidence or knowledge] that weather will be more extreme. There would be a lot more "air" to get moving and therefore a lot more energy involved.
> Season will depend on the shape of the planet's orbit and axial tilt...
> [I can remember a SF story from years ago about gas miners finding life in the gasses of Jupiter. They had to fight 1000mph winds of corrosive acid as well as gas-whale creatures that were 20 miles long...]
> One thing I'd mention... Dyson sphere... Not exactly what you are talking about...



Yeah, a little apocalyptically bad weather once and a while would be fine, you'd just need to have the people build their cities like bunkers. Thousand mile per hour winds being normal would make the planet unlivable, to anything even remotely human.
I'll check up on the weather thing.




Terry Greer said:


> Tides do depend on the size and distance of the moons. Earth is particularly unusual in the size of it's moon relative to its own mass.
> But tides don't need to just affect the oceans - they'd have an impact on atmosphere as well - especially dense air. Fogs and mist from the depths could be synchronized with the moons - and they would be your tides. If the atmosphere is toxic at those times - that would be interesting.
> 
> Cup of Joe is right in that multiple moons would probably smear out any tidal effects, although you could get around this to some extent by having the moon orbits in harmonic resonant frequencies - something that tends to happen. But the tides can be detected even in the larger lakes. The force of the tides on earth is more a matter of ocean currents and coastal regions funnelling water movement.  E.g. in the med the average tidal range is less than 2 feet and there are several places where no range is visible at all. Most of these currents are set in motion by heat exchange and not by the moon at all.
> ...



I'm leaning towards the world being a construct of some kind. It's construction and how all the race wound up living there will be some a myth  that they collectively share. 

If i'm interpreting the orbital-resonance correctly, then objects of similar mass and proximity will balance out the others gravitational influence and act single body exerting a combined influence.  So it wouldn't be multiple moons effecting the tied, the biggest and closest moons will "sync" and exert a combined influence;tidal surges are something that i'm fine with. Only two maybe three of the moons are large enough to matter.






Hainted said:


> If you really want the endless world hopping expanse of a space opera without the headache of interstellar travel than I wouldn't make the giant planet livable, I would make the moons livable. As long as the giant itself sits in the habitable zone multiple moons would be capable of supporting life. Imagine one moon with an erratic orbit, home to a warlike race that attacks whatever other moon they come near before retreating. Hmmmm?
> 
> But to get back to the original question, Reddit's Astrophysics forum helped me out a lot when I was designing my binary planet system for a story, and several physics forums around the net have sections dedicated to writers posing questions to help make their stories more plausible.



Thankyou, the site that I've been using lately is the world building stack exchange , there're helpful but sticklers for the proper format. If i can't find answers more satisfying than hand handwavium i may just just follow trough with making the moons habitable. One of my earlier ideas was for a single massive solar like nBSG  or Firefly's Vers. Having everybody on one massive planet invokes a feeling both familiar and foreign; and keeps the rules of combat terrestrial.  

Aside from things like great winged beasts, floating forests and a exotic ecology lurking beneath the toxic sea. Is the idea that the people of this world either don't have easy access to metal  or their are a number of materials and processing methods that are cheaper than metal craft.

What could used in the absence of metal and how would this effect the people? the first things that come to my mind as metal substitutes  specially treated wood and fabrics,incredibly plant or animal fibers, ceramic and certain types of crystal or stone.


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## Penpilot (Feb 14, 2015)

This gave me an excuse to see if I could still do some rudimentary physics calculations. All numbers are approximations, and although I double checked my calculations, I still reserve the right to be wrong.

If a planet the size of Jupiter had the same density as Earth, its gravitational pull on the surface would be 103.49m/s^2. Earth's gravitational pull is 9.8m/s^2. A 100kg man would weigh 10055kg  or 22168lbs.

Its escape velocity would be 120km/s or 270 000 mph or mach 334.  Earth's escape velocity is 25000mph or mach 33.

Even though this Jupiter-sized planet would be approximately 1200 times more massive than Earth, its surface area would only be 120 times that of Earth. Not sure if that would be enough to classify as feeling endless. I guess that would depend on mode of travel available.

With the math out of the way. I'd also agree that the atmosphere would be really thick because of the strong gravity. Jupiter's atmospheric pressure is 10 times that of Earth's. With a thick atmosphere there may be a greenhouse effect, so the planet could really be warm. Also with a thicker atmosphere, there's more stuff for the gravity of the moons to grip onto and pull on, so the weather pattern swings may be greater, but I think you could shape this how ever you want because I'm sure there's a orbital configuration for the moons that would produce what ever weather and tide pattern you want. 

Say you have two or more moons lined up on one side of the planet, that could create a massive tided flow in that direction. But if you had another moon on the opposite side at the same time, it could lessen tidal effects or negate them.

The night skies would probably be brighter with all those moons to reflect light. And there probably wouldn't too many moonless nights.


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## CupofJoe (Feb 15, 2015)

Penpilot said:


> Say you have two or more moons lined up on one side of the planet, that could create a massive tided flow in that direction. But if you had another moon on the opposite side at the same time, it could lessen tidal effects or negate them.


From what I understand of tides on Earth, the tides peak towards and opposite our moon... so a moon on the other side of the giant planet could make their tides worse...


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## Terry Greer (Feb 15, 2015)

You might find this link interesting:

Utility - Planet Designer

Its a calculator for creating planetary data. If you did go for a planet poor in metals without a nickel iron core you could probably reduce the average density to around half that of earth - and then play around with the numbers. 

I tried it and ended up with a planet twice the radius of earth - so roughly 4x the area of the earth's surface - with a mass 3 times that of earth but an average g of just 1.01 (almost identical).

Now if the world was hollow! and the mass much lower you could go much bigger.


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## Hainted (Feb 15, 2015)

I think a Dyson Sphere or a Ringworld would solve the problem of an "endless "world without delving into space travel. You would get millions of times the surface area of even a Jupiter size planet( something like 3 million Earths if I remember correctly. Your people may not even realize they live on it. Subterranean races would just run into "The Layer" which the gods put in place to keep them from tunneling into hell and releasing the damned. At the edges, or walls would be impossibly tall insurmountable mountain ranges where the gods live. A smaller counter-ring would rotate in the opposite direction with gaps to allow for a day/night cycle. The dead, and any abandoned structures would be  reclaimed by Gaia (or whoever) to be reborn in the next cycle (nanomachines break them down to ensure the inhabitants don't run out of materials for their civilizations.


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## K.S. Crooks (Feb 15, 2015)

Seasons are determined by the tilt of a planet's axis and the rotation time around its star. For a specific region on a planet the distance from the equator, the path of ocean currents and placement of large geological structures such as mountains also are a factor.

World weather patterns are affected by the rotation speed of the planet. Local weather patterns are further affected local phenomena such as lakes, rivers and altitude.

For the tides it depends on the mass of the moon(s). The greater the mass and the closer it is to the planet the larger the high and low tide difference will be. The more moons you have the greater the chance for there to be a cancellation of forces, especially if you have some moons orbit in another direction or along another plane. Think 3-dimensionally for the way orbits can go.
Also understand that the moons will not be the same distance from the planet, otherwise they would eventually collide. The farther a moon is from the planet the less effect it will have on the tide. If you want two moons to have the same tidal influence then the farther one needs to have a greater mass. Hope this helps.


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## Penpilot (Feb 15, 2015)

CupofJoe said:


> From what I understand of tides on Earth, the tides peak towards and opposite our moon... so a moon on the other side of the giant planet could make their tides worse...



Yeah, but it can get pretty complicated. I am definitely no expert, but here's how I'm seeing it. The tidal bulge opposite the moon is cause by the rotation of the Earth-Moon system around its common center of mass. Depending on where that center of mass is, it could definitely make the tides worse in a two moon system. But if the center of mass was directly a the center of the planet, there would be no centrifugal force causing the secondary bulge. 

In a multi-moon system it might get pretty wacky, as mentioned above, different orbital planes, different masses, and different distances. The distances adds another level of complexity here. Even if the orbital paths were perfectly circular, if the center of mass isn't dead center of the planet, the the orbital distance between each moon and the planet will constantly be changing, so gravitational pull will increase and lessen.

Now throw in the gravitational influences of the other planets and bodies... and my head explodes. 

After that long winded babble, what I'm basically trying to say is with all these different variables at play, one can just arbitrarily choose a tidal pattern and there will probably be a orbital configuration that will cause it.


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## Logos&Eidos (Feb 15, 2015)

Penpilot said:


> This gave me an excuse to see if I could still do some rudimentary physics calculations. All numbers are approximations, and although I double checked my calculations, I still reserve the right to be wrong.
> 
> If a planet the size of Jupiter had the same density as Earth, its gravitational pull on the surface would be 103.49m/s^2. Earth's gravitational pull is 9.8m/s^2. A 100kg man would weigh 10055kg  or 22168lbs.
> 
> ...



Thank you for the math. The world while big doesn't have the density that a planet of it's sizes naturally formed would have.   



CupofJoe said:


> From what I understand of tides on Earth, the tides peak towards and opposite our moon... so a moon on the other side of the giant planet could make their tides worse...



Your going to have to clarify why would a moon moving  in the opposite directing make things worse?



Terry Greer said:


> You might find this link interesting:
> 
> Utility - Planet Designer
> 
> ...



The world isn't hallow but it's interior is definitely different from earth.And yes i am going much bigger!    



Hainted said:


> I think a Dyson Sphere or a Ringworld would solve the problem of an "endless "world without delving into space travel. You would get millions of times the surface area of even a Jupiter size planet( something like 3 million Earths if I remember correctly. Your people may not even realize they live on it. Subterranean races would just run into "The Layer" which the gods put in place to keep them from tunneling into hell and releasing the damned. At the edges, or walls would be impossibly tall insurmountable mountain ranges where the gods live. A smaller counter-ring would rotate in the opposite direction with gaps to allow for a day/night cycle. The dead, and any abandoned structures would be  reclaimed by Gaia (or whoever) to be reborn in the next cycle (nanomachines break them down to ensure the inhabitants don't run out of materials for their civilizations.



After thinking it over I've decided to embrace the Dyson sphere concept for my world,  I've got more land  than I'll ever use, a method of fast travel will defiantly be necessary.  Looking into the lore of my setting i have place and time to fit this giant planet. Durring the first war of the gods the cosmos was all but destroyed leaving, this world was constructed in in the last remaining area in existence. It was meant as as a home for the surviving sapient races, the planet would be lit from within by a perpetual power. who's energies fire the world's alchemical processes. Great plateaus and rocky peaks rise from and slowly move around an alchemical sea.



K.S. Crooks said:


> Seasons are determined by the tilt of a planet's axis and the rotation time around its star. For a specific region on a planet the distance from the equator, the path of ocean currents and placement of large geological structures such as mountains also are a factor.
> 
> World weather patterns are affected by the rotation speed of the planet. Local weather patterns are further affected local phenomena such as lakes, rivers and altitude.
> 
> ...



If I'm following you right, then the planets sizes is not the greatest influence on weather it's rotational  speed, solar proximity and axle inclination.   Then despite the world being millions of time the sizes of earth the overall climate would be fairly equivalent to the real world; though i can only imagine the effect of  the world being so large on weather patterns.


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