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World building idea: Jupiter-sized Earth

Marc_C

Solitary Role Playing
"What is Jupiter's gravity compared to Earth?

Although Jupiter is a great deal larger in size, its surface gravity is just 2.4 times that of the surface gravity of Earth. This is because Jupiter is mostly made up of gases. If you weigh 100 pounds on Earth, you would weigh 240 pounds on Jupiter (assuming you could find someplace to, well, stand)."

Exosuits or augmented bone, muscles and biology. I recall an old sci-fi story in which aliens who evolved in Jupiter are crocodile-like because of gravity. They don't walk upright. They walk on four legs.
 

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MarkB

Legend
"What is Jupiter's gravity compared to Earth?

Although Jupiter is a great deal larger in size, its surface gravity is just 2.4 times that of the surface gravity of Earth. This is because Jupiter is mostly made up of gases. If you weigh 100 pounds on Earth, you would weigh 240 pounds on Jupiter (assuming you could find someplace to, well, stand)."

Exosuits or augmented bone, muscles and biology. I recall an old sci-fi story in which aliens who evolved in Jupiter are crocodile-like because of gravity. They don't walk upright. They walk on four legs.
Yeah, but as stated in your quote, that's because Jupiter is mostly gas. A solid planet the size of Jupiter would have much higher gravity.
 

Umbran

Mod Squad
Staff member
The hollow shell world is what I was thinking. Gaseous core supporting a solid exterior, with seas that are deep from a human perspective but not in comparison to Earth.

This has a major advantage over a Dyson Sphere - gravity.

In a modern Dyson sphere, you have a star (or similar object) in the center, and people living on the inside of a sphereical shell around it. This leaves a big question as to why people (and, say, atomsphere) sticks to the inside of the shell, and not pulled into the star. You need big honkin' gravity generators or something to make it work.

A shell world, however, has people livign on the outside, which makes more gravitational sense.

A shell world, however, is extremely vulnerable to impacts. One biggish asteroid puncturing the shell, and your sea empties into the shell.
 


aco175

Legend
You also need to figure out the cycles of the day. A 24 hour day like Earth may be a problem with things like wind speed and storms being able to travel longer while picking up speed. Typical storms may be hurricane-like. This may be cool to have air ships that are able to ride the wind and transport faster than ground or water shipping.

My 1/day recharge power or slow healing rate would suck.
 

Mercurius

Legend
Lots of good replies, thanks. I'll re-read them to tease out ideas and considerations.

I think a lot of it comes down to where on the spectrum of scientific realism I want to place myself, with the major demarcations being hard sf, soft sf, and fantasy (with lots of gradations in-between). For my purposes, I'm looking at somewhere between soft sf and fantasy, so issues around gravity, planetary density, etc, don't matter--or at least don't have to be explained (still fun to think about, though).

Actually, this brings up a tangential--but related--issue, which is the question around, what approach to big questions do I want to take? Hard sf tends to take the approach of trying to scientifically explain how something that we normally wouldn't understand works, given our current scientific paradigm. Much of it is written by professional scientists, and all of it by the scientifically literate. For them, the joy is answering those questions, if only speculatively and theoretically.

My preferred approach is more about exploring the mystery, and using it as a context for story. We could call this the "Terra Incognita approach": there are always places on the map that are unexplored and unknown, or cannot be explained by our current tools of cognition, and perhaps imply places off the map. I mean, the horizon always recedes. This is not to say that I don't like coming up with explanations, but that I don't feel beholden to scientific canon, circa 2021.

That said, whatever approach I take, a lot of the same questions can considered. How does the world work? Hard sf, soft sf, and fantasy all have different requirements, yet all do require certain things: internal consistency and some degree of verisimilitude.

For instance, Jupiter has 120x the surface area of Earth. Would the world have continents and oceans that are proportionally the same, or from orbit would it look like countless smaller landmasses and islands? Meaning, would it still have about six major landmasses, three larger than the rest, that are a hundred times as large as our continents, or would it have hundreds of such continents? Or, my likely answer, a bit of both?

And what about life? Would this world have flora and fauna similar in size to Earth, or would it have a wider range, with perhaps gargantuan trees like the theory that the Devil's Tower is actually a primeval petrified tree stump?

Or what about the length of the day? And the range of climate? Etc etc.

p.s. After posting the OP, I did remember Jack Vance Big Planet and Robert Silverberg's Majipoor books.
 

Mustrum_Ridcully

Adventurer
This has a major advantage over a Dyson Sphere - gravity.

In a modern Dyson sphere, you have a star (or similar object) in the center, and people living on the inside of a sphereical shell around it. This leaves a big question as to why people (and, say, atomsphere) sticks to the inside of the shell, and not pulled into the star. You need big honkin' gravity generators or something to make it work.

A shell world, however, has people livign on the outside, which makes more gravitational sense.

A shell world, however, is extremely vulnerable to impacts. One biggish asteroid puncturing the shell, and your sea empties into the shell.
A shell world doesn't really sound like somethin that occurs "naturally", so I think some magic or unusual non-realistic physics are bound to exist - maybe there simply are no asteroids like that in this universe, or something that protects the world - maybe the Gods, or some other, more alien supernatural or technological beings.

Maybe one time that protection was broken, and so an asteroid crashed, and there is actually a sea that's slowly but inevitably being drained. Which could be the cause of a big struggle and/or migration. That could be something that's ongoing, or somehting that happened in the past. Maybe someone intervened - gods, mages, engineers - to close the hole again and stop the drain. But in the mean time, land bridges opened up that enabled contact between groups that never had contact before.

I am kinda partial over all to keep the oceans and continents as large as on Earth, I think. That means they are not unsurmountable obstacles by non-magical means, but still really challenging. The different oceans would be seperated from each other (so you could feasibly have a few drained).

Empires spanning multiple continents would still be impractical, unless you have reliable means of magical communication or transportation, since otherwise a revolution on another continent has alread exchanged continental leadership before the leaders of the other continent could respond.

But an interesting question - assuming human migration patterns as they were, but Earth was 11 times larger, but with continents and oceans the same size as now - how far could we have spread until, say, the 5th century or the 15th century? WOuld we have probably populated all continents, or would still some be left alone? How long ago could they have been settled by some humans? Maybe the humanoid species all hail from the first settlers and changed due to the continents they live (be it by evolution, genetic manipulation or magic?). A drain event could be the cause for some recently increased contact between groups that had no contact before.
 

Marc_C

Solitary Role Playing
But an interesting question - assuming human migration patterns as they were, but Earth was 11 times larger, but with continents and oceans the same size as now - how far could we have spread until, say, the 5th century or the 15th century? WOuld we have probably populated all continents, or would still some be left alone? How long ago could they have been settled by some humans? Maybe the humanoid species all hail from the first settlers and changed due to the continents they live (be it by evolution, genetic manipulation or magic?). A drain event could be the cause for some recently increased contact between groups that had no contact before.
With such a set up another sentient race could have evolved separately from Homo sapiens like in the novel West of Eden by Harry Harrison. Direct descendants of dinosaurs survived and evolved into a bipedal intelligent specie.

 

doctorbadwolf

Heretic of The Seventh Circle
This has a major advantage over a Dyson Sphere - gravity.

In a modern Dyson sphere, you have a star (or similar object) in the center, and people living on the inside of a sphereical shell around it. This leaves a big question as to why people (and, say, atomsphere) sticks to the inside of the shell, and not pulled into the star. You need big honkin' gravity generators or something to make it work.

A shell world, however, has people livign on the outside, which makes more gravitational sense.

A shell world, however, is extremely vulnerable to impacts. One biggish asteroid puncturing the shell, and your sea empties into the shell.
Yeah definitely need some kinda solve for that.

Interestingly, IIRC Halo rings from Halo are really good models for Dyson sphere style habitations, because thier spin can evenly and reliable simulate gravity, although stuff will still fall “up” toward the thing you’re in orbit around, so some sort of secondary structure to catch things and people that get yeeted would be a good idea. Theoretically you don’t even have to enclose the ring, but you might as well since you need stuff to not get yeeted into the sun or space, and you’re a bit safer against impacts.

but none of that fixes our eggshell world problem.

is there any gas that water would sit on top of? If such a gas was what fills the inside, you could float seas on it, making a sea that the depths of are a gas that you prolly can’t breath. Scary stuff, but also it’s a fantasy world so what lives in the core?
 

GuyBoy

Adventurer
Lots of good replies, thanks. I'll re-read them to tease out ideas and considerations.

I think a lot of it comes down to where on the spectrum of scientific realism I want to place myself, with the major demarcations being hard sf, soft sf, and fantasy (with lots of gradations in-between). For my purposes, I'm looking at somewhere between soft sf and fantasy, so issues around gravity, planetary density, etc, don't matter--or at least don't have to be explained (still fun to think about, though).

Actually, this brings up a tangential--but related--issue, which is the question around, what approach to big questions do I want to take? Hard sf tends to take the approach of trying to scientifically explain how something that we normally wouldn't understand works, given our current scientific paradigm. Much of it is written by professional scientists, and all of it by the scientifically literate. For them, the joy is answering those questions, if only speculatively and theoretically.

My preferred approach is more about exploring the mystery, and using it as a context for story. We could call this the "Terra Incognita approach": there are always places on the map that are unexplored and unknown, or cannot be explained by our current tools of cognition, and perhaps imply places off the map. I mean, the horizon always recedes. This is not to say that I don't like coming up with explanations, but that I don't feel beholden to scientific canon, circa 2021.

That said, whatever approach I take, a lot of the same questions can considered. How does the world work? Hard sf, soft sf, and fantasy all have different requirements, yet all do require certain things: internal consistency and some degree of verisimilitude.

For instance, Jupiter has 120x the surface area of Earth. Would the world have continents and oceans that are proportionally the same, or from orbit would it look like countless smaller landmasses and islands? Meaning, would it still have about six major landmasses, three larger than the rest, that are a hundred times as large as our continents, or would it have hundreds of such continents? Or, my likely answer, a bit of both?

And what about life? Would this world have flora and fauna similar in size to Earth, or would it have a wider range, with perhaps gargantuan trees like the theory that the Devil's Tower is actually a primeval petrified tree stump?

Or what about the length of the day? And the range of climate? Etc etc.

p.s. After posting the OP, I did remember Jack Vance Big Planet and Robert Silverberg's Majipoor books.
I’d be like you with going soft on the scientific side of the planet and just play with the fun aspects of its vast size.
My best guess into flora and fauna would be incredible diversity, due to complete inability to contact. Think marsupials in Australasia but on speed, with absolutely no contacts with other continents, even in the form of flying animals or floating vegetation mats. Megafauna and megaflora could easily exist, and evolutionary niches may show some parallels, but also some significant differences due to climate and geology.
A vast, heavily volcanic continent would spawn?
A swamp the size of Asia,inhabited by?
What lives in a river the width of Europe?
How large are the herds of ? on a savannah larger than the USA?

The concept of “the Ancients” is cliched, but also might answer scientific impossibilities and also leave behind gates.
One vast continent could have a few “points of light” settlement alongside a completely mercantile travelling culture, who spend entire lives moving between settlements, with whole generations passing between returns to the same place.
And the prospects for diversity of cultural developments are vast.
 


doctorbadwolf

Heretic of The Seventh Circle
Lots of good replies, thanks. I'll re-read them to tease out ideas and considerations.

I think a lot of it comes down to where on the spectrum of scientific realism I want to place myself, with the major demarcations being hard sf, soft sf, and fantasy (with lots of gradations in-between). For my purposes, I'm looking at somewhere between soft sf and fantasy, so issues around gravity, planetary density, etc, don't matter--or at least don't have to be explained (still fun to think about, though).

Actually, this brings up a tangential--but related--issue, which is the question around, what approach to big questions do I want to take? Hard sf tends to take the approach of trying to scientifically explain how something that we normally wouldn't understand works, given our current scientific paradigm. Much of it is written by professional scientists, and all of it by the scientifically literate. For them, the joy is answering those questions, if only speculatively and theoretically.

My preferred approach is more about exploring the mystery, and using it as a context for story. We could call this the "Terra Incognita approach": there are always places on the map that are unexplored and unknown, or cannot be explained by our current tools of cognition, and perhaps imply places off the map. I mean, the horizon always recedes. This is not to say that I don't like coming up with explanations, but that I don't feel beholden to scientific canon, circa 2021.

That said, whatever approach I take, a lot of the same questions can considered. How does the world work? Hard sf, soft sf, and fantasy all have different requirements, yet all do require certain things: internal consistency and some degree of verisimilitude.

For instance, Jupiter has 120x the surface area of Earth. Would the world have continents and oceans that are proportionally the same, or from orbit would it look like countless smaller landmasses and islands? Meaning, would it still have about six major landmasses, three larger than the rest, that are a hundred times as large as our continents, or would it have hundreds of such continents? Or, my likely answer, a bit of both?

And what about life? Would this world have flora and fauna similar in size to Earth, or would it have a wider range, with perhaps gargantuan trees like the theory that the Devil's Tower is actually a primeval petrified tree stump?

Or what about the length of the day? And the range of climate? Etc etc.

p.s. After posting the OP, I did remember Jack Vance Big Planet and Robert Silverberg's Majipoor books.
Yeah I think the approach you seem to be leaning toward is best. Answering the “hard sf” questions around gravity, density, materials, etc, can lead to a more interesting and even a more fantastical world.

I mean one world we could imagine is a Jupiter with a high oxygen content, and a halo ring of rocky debree that has grown flora and fauna on the interior of the ring, getting only a couple hours a day of direct sunlight, and constant very low light from a molten core or from refraction within the gas cloud that makes up most of the planet. Water condenses on the ring, freezing on the exterior and liquid on the interior, and life is tenuous but hardy. Up is, in a very real sense, down. Perhaps there is an ocean, and that ocean is above your head and you will fall into it, and maybe sink all the way into the gaseous core below it, if you jump or fly too high and lose control.
 

Umbran

Mod Squad
Staff member
Yeah definitely need some kinda solve for that.

Interestingly, IIRC Halo rings from Halo are really good models for Dyson sphere style habitations

So, while you cite Halo, the concept is much older, and was covered in depth by Larry Niven in his Ringworld books. He worked with a ring whose radius was approximately the radius of Earth's orbit, with a star at the center, as a way to get massive inhabitable area around a star, without having to have gravity generators to keep things on the structure like is required by Dyson Spheres.

Halo's rings are much smaller - only 5000 km in radius. The Earth would fit within one, but not a star.

because thier spin can evenly and reliable simulate gravity, although stuff will still fall “up” toward the thing you’re in orbit around,

No, generally things don't fall up unless you're putting a small ring around a massive object, and don't spin it fast enough. That's the point of spinning - if you spin the ring, stuff sticks to the floor. You put walls on the sides to keep the atmosphere in. Some air leaks out slowly into space, but that happens on planets, too.

is there any gas that water would sit on top of?

Not within the temperature and pressure range where water is liquid, no.
 

Mercurius

Legend
Yeah I think the approach you seem to be leaning toward is best. Answering the “hard sf” questions around gravity, density, materials, etc, can lead to a more interesting and even a more fantastical world.

I mean one world we could imagine is a Jupiter with a high oxygen content, and a halo ring of rocky debree that has grown flora and fauna on the interior of the ring, getting only a couple hours a day of direct sunlight, and constant very low light from a molten core or from refraction within the gas cloud that makes up most of the planet. Water condenses on the ring, freezing on the exterior and liquid on the interior, and life is tenuous but hardy. Up is, in a very real sense, down. Perhaps there is an ocean, and that ocean is above your head and you will fall into it, and maybe sink all the way into the gaseous core below it, if you jump or fly too high and lose control.
Very cool - so many possibilities!

I find that considering the hard science gives frameworks and considerations for choices, even if I stick within the soft sf/fantasy range of explanations.

I also like the idea of a "Swiss cheese world" that is so riddled with pockets (and perhaps micro-ecologies) that it is far lighter than a big planet would normally be.

My understanding of science is limited, but while I realize that gravity is believed to be constant throughout the universe, this is still only theoretically true. I mean, we can't know for certain, right? Perhaps there are galaxies with different degrees of gravity, or even pockets within galaxies. Perhaps even worlds that operate by different physical laws.

Although, again, I don't need to explain or rationalize this for my purposes, although it may be somewhat important in my story idea, because the protagonist--while not a scientist--is still a member of a technologically advanced civilization (Earth at the end of the 21st century), so would have some knowledge, and at least I'd want a sense of when I'm "breaking the rules."
 


Davies

Hero
Temp 292K Base 19C (Earth is 14C)
Gravity 8.0 m/s^2 (0.82 Earth Gravity)
3.8 x 10^6 (3,800,000) km radius = 181,458,391,671,347 km^2, Earth's area is 510,065,623 km^2
The dyson is 355,755 times the size of the Earth in area of km^2

At this scale, planetary circumnavigation is not something that can be accomplished within a single human lifespan, absent magic like life extension.
 

Tonguez

A suffusion of yellow
The other big issue is that your atmosphere will be enormous, dense and hydrogen rich which, if life sustaining, would allow for bigger aerial creatures swimming through the sky.

On the surface the dense atmosphere would lead to a flatter topography. You’d need to handwave the huge gravity although a water planet with only a few islands would provide a lower overall density.
Imagine the core as small, dense and hot. Volcanically active but with a thick crust that limits magma break through.
 
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Umbran

Mod Squad
Staff member
Empires spanning multiple continents would still be impractical, unless you have reliable means of magical communication or transportation, since otherwise a revolution on another continent has alread exchanged continental leadership before the leaders of the other continent could respond.

Note that several human empires on Earth spanned multiple continents.

But an interesting question - assuming human migration patterns as they were, but Earth was 11 times larger

Nitpick: "11 times larger" can mean several things. 11 times the mass, 11 times the radius, 11 times the surface area. I'll assume we are talking Jupiter-sized, so about 120 times the surface area of Earth.

, but with continents and oceans the same size as now - how far could we have spread until, say, the 5th century or the 15th century?

So, assume humans have a central origin point, and spread out?

Humans left Africa in several waves, but we can use the last, largest one as our model - It started maybe 60,000 years ago (there's a question, making for a broad window of when it started), and modern humans had covered Africa, Europe, Asia, and Australia in about 5,000 to 10,000 years.

Then, we were stalled. The Pacific and Atlantic oceans were effective barriers. There's a lot of question as to when humans first reached the Americas. However, once we got here, spread was fairly quick, reaching most parts of North and South America within a couple thousand years.

So, naive analysis might say, humans can cover an Earth-sized area in about 10K years. However, we note that the real limiter was available paths to new land.

One model might be - pick a continent for an origin. Every adjacent landmass will be occupied within 2k to 5k years. And by adjacent we mean, connected by traversable land, or separated by a water barrier of less than 100km. Then, from those land masses, you can move to the next over the next few thousand years, and so on. How far you get depends on how connected the landmasses are.
 

Umbran

Mod Squad
Staff member
My understanding of science is limited, but while I realize that gravity is believed to be constant throughout the universe, this is still only theoretically true. I mean, we can't know for certain, right?

Um... yes and no. That brings up some very hairy questions of physics, and some very weird things happen when the rules are not the same everywhere. It is likely that without the assumption that physical laws are the same throughout the universe, the result is apt to be unstable, and areas will collapse until you reach a point where the Universe has the same laws everywhere.

Perhaps there are galaxies with different degrees of gravity, or even pockets within galaxies. Perhaps even worlds that operate by different physical laws.

No. That would be observable with current technology, and would have... repercussions that might well destroy a galaxy, as stars tried to move from one region to another, and were destroyed in the process.
 

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