Question Jupitearth

Sep 20, 2021
6
7
15
I'm writing a story, which is to take place on a gigantic planet. In this story, lots of mysterious and impossible things will happen, but I want the stage to be believable - realistic, actually. After doing a little research, I found why Earth-like planets can only be ~3,5 times bigger.. But I need much more space. And also a moon, that doesn't crash into this huge planet.. I really hope there is someone on here who's an expert in theoretical astronomy, who can help me find a way to 'build' this planet, without breaking the rules of physics.. Any help is welcome, as I really am out of my depth here. As soon as I find a way to make a non-imploding super-Earth the problem of super-weather presents itself of course, but I'm getting ahead of myself ;)
 
  • Like
Reactions: Catastrophe
Mar 9, 2021
6
5
15
Have you read any of Robert Silverberg's "Majipoor" series? He writes about an extremely large planet with a far less dense core than an earth-like planet, thus giving earth-like gravity on a gas giant sized planet. Check out "Lord Valentine's Castle" and "Valentine Pontifex".
 
  • Like
Reactions: Catastrophe
Sep 20, 2021
6
7
15
Thanks for your fast response! I did not read the books you mentioned, I came up with that idea myself too though. But is that possible? If the core is less dense, gravity is affected too, and without a big iron core, there would be no magnetic field either, right? I can dream up a supersized planet, thats isn't the issue, but I want the planet itself to be physically possible, without it being engineered by godlike aliens or something similar, which is also a solution to this problem. I want the universe as we know it to be able to produce this superplanet, even if the chances are very, very slim ;) I want vulcanism, plate tectonics, all the things we have here too. I have much more questions, as you can imagine, about the weather and the possible role of the moon in that. But I want to know what the planet is made of first.
 
  • Like
Reactions: Catastrophe

Catastrophe

The devil is in the detail
Does it have to be one large planet, or could you have two large planets circling each other in orbit around the star, like larger versions of Pluto and Charon?

Cat :)
 
Sep 20, 2021
6
7
15
Does it have to be one large planet, or could you have two large planets circling each other in orbit around the star, like larger versions of Pluto and Charon?

Cat :)
It has to be one big planet, to suit my plans. Two planets would of course create a totally different society - a very interesting idea but not what I'm looking for.
 
  • Like
Reactions: Catastrophe
Sep 20, 2021
6
7
15
Can the people be smaller instead? 😀
No, they can't - I think. I've really given this a lot of thought, and this idea also popped into my brain. It does solve the equation - it does. I like the idea, but it would totally change the story, just like the idea of two planets. Also, there's already little people ;) If I shrink my humanoids down to insect-size they would have plenty of space, but they would replace the tiny people - unless I shrink those even more, of course.. You couldn't know this, but I plan to write a lot about fictional biology within the story, and if everyone's a gnome their perspective on the planet would be totally different - the contact with the surrounding nature would be changed entirely. Full disclosure: I'm keeping this idea as a plan B, if the super-Earth will turn out to be 'too impossible' ;) Thanks for responding!
 
Last edited:
Jun 1, 2020
1,694
1,445
3,560
Ok. There are some simple equations you might want to play with. They are easy to work with if you use them in ratios with Earth.

The surface area is simply the square of the radius. So, if you, say double the radius, you’ll get 4x Earth’s surface area.

But the volume increases by the cube of the radii ratio. So, with R=2, then you’ll have 8x the mass. The gravity force at the surface, however, is only 2 g since gravity drops as the inverse square.

Or...R^3/R^2 = 8/4 = 2g.

You can reduce the density with a smaller iron core ratio by increasing the rotation rate, which also reduces the grav force near the equatorial regions. I doubt you need much more iron than what Earth has already to get you mag. field.
 

Catastrophe

The devil is in the detail
Yes, more volume for subterranean domiciles:

"So, with R=2, then you’ll have 8x the" volume. And if it's hollow, the mass is not increased that much.
Is that what you meant, Helio?

Cat :)
 
Jun 1, 2020
1,694
1,445
3,560
Yes, more volume for subterranean domiciles:

"So, with R=2, then you’ll have 8x the" volume. And if it's hollow, the mass is not increased that much.
Is that what you meant, Helio?

Cat :)
With an increase in radius to twice that of Earth, the gravity is only double if the density is the same.

But if you bump the spin rate, you could argue for as strong a mag field even with less than an Earth-mass of iron. Thus, both the lower density and higher spin rate, perhaps the gravity would be roughly 1.25 to 1.75g.

It depends on just how much more area is required.
 
  • Like
Reactions: Catastrophe
Sep 20, 2021
6
7
15
Ok. There are some simple equations you might want to play with. They are easy to work with if you use them in ratios with Earth.

The surface area is simply the square of the radius. So, if you, say double the radius, you’ll get 4x Earth’s surface area.

But the volume increases by the cube of the radii ratio. So, with R=2, then you’ll have 8x the mass. The gravity force at the surface, however, is only 2 g since gravity drops as the inverse square.

Or...R^3/R^2 = 8/4 = 2g.

You can reduce the density with a smaller iron core ratio by increasing the rotation rate, which also reduces the grav force near the equatorial regions. I doubt you need much more iron than what Earth has already to get you mag. field.
Now THIS is the kind of answer I was looking for! I know that, because I didn't understand it immediately. I understand the first part, about the relation between the radius and the surface. I also understand what you said about the relation between the radius and the mass. This, I don't understand: "The gravity force at the surface m, however, is only 2 g since gravity drops as the inverse square." I know what you mean by inverse square, but where do these m and g suddenly come from? Doesn't it depends greatly on the matter the hypothetical sphere is made of how many g there is on the surface? I'm sure I sound very dumb to everyone here, but I don't care - I really want to know. I also understand what you say about the density and the rotation rate. But about the iron core; wouldn't it also have to be gigantic to have a similar effect on the giant-Earth's surface-life and it's place in the cosmic dance when compared to earth? I don't know much about Earth's magnetism either, so again; I apologize in advance for sounding stupid ;) And how fast can I make a huge planet spin without destroying all life on it? I've thought a lot about gravity too,I actually have more questions about that..I would actually like to have high-gravity, normal gravity and zero-gravity zones on the planet.. I don't know if that's possible. If not, then it will just be 'normal' gravity everywhere. Among other things: is it possible to have mountain with much lower gravity at the top, as in: weightlessness at the peak and 'normal' gravity at it's base around sealevel? Another question in a different direction: I don't want any snow or ice, not even at the poles - I would actually like the entire planet to have the same, warm climate everywhere. Maybe a little at the peak of the highest mountain, but no more. Could a complex but stable rotation pattern that isn't like Earth's provide that, or is that impossible? Also: I want the part of the atmosphere we can easily breathe and fly around in to be much thicker too, nothing close to the ~16 km we have on Earth, I need much more. Of course that will make the predicting of weatherpatterns even more complicated, just like messing around with the rotation.. I'm only getting myself into more trouble - I know..

With an increase in radius to twice that of Earth, the gravity is only double if the density is the same.

But if you bump the spin rate, you could argue for as strong a mag field even with less than an Earth-mass of iron. Thus, both the lower density and higher spin rate, perhaps the gravity would be roughly 1.25 to 1.75g.

It depends on just how much more area is required.
I would like to have a very thick top layer - compared to Earth - of various relatively soft stone below the dirt of the surface, below these soft rocks I would like an even thicker layer of harder stone that is perforated by subterranean water streams. Below that, bedrock, and below that the planet's plate tectonics. But I'm afraid this is impossible at Jupiter's scale (~11 times wider than Earth), it would all implode - inevitably. But I really do need loads of space, both in the atmosphere above the surface ánd underground.. Or wouldn't it implode, would the lavaball inside this planet burst through the surface, because of it's size? I really wouldn't know. Thanks, so much, for helping me.
 
Last edited by a moderator:
  • Like
Reactions: Catastrophe
Jun 1, 2020
1,694
1,445
3,560
I know what you mean by inverse square, but where do these m and g suddenly come from? Doesn't it depends greatly on the matter the hypothetical sphere is made of how many g there is on the surface?
Yes, if we start with a density equal to Earth, then the total mass increase will be equal to the volume increase.

V = 4/3 pi R^3

But with using ratios with Earth, then it gets easier. Namely...

V increase = (Rn/Re)^3 [Rn is the new planet radius]

Using a radius increase of, say, 2 gives a volume of 8x (2^3) Earth. So the mass is also 8x greater.

But the gravitational force, g, won’t be 8g because the distance to the surface is 2x farther. And its an inverse square law reduction. So at 2Re, then the gravity is 1/4th as much. So the product gives the result of 2g. [8x more mass but 1/4 due to surface distance.]

For Rn = 3Re, then the surface gravity is 3g, but you now have 9x the surface area. [4 pi R^2]

There are two ways to reduce this strong gravity: reduce the density; increase the rotation rate. The latter won’t help polar regions, however.

Earth has more iron for its size than any other planet, so its more dense than it needs to be. But a more massive planet will have greater gravity thus will likely be more dense, iron or not. Large low density planets are gas or ice giants and tricky to make habitable, IMO.

But about the iron core; wouldn't it also have to be gigantic to have a similar effect on the giant-Earth's surface-life and it's place in the cosmic dance when compared to earth?
Well, our mag field goes well beyond our surface and gives great protection, even now when it’s weaker than average and may be flipping in the not too distant future. It’s plausible to assume Earth’s field, especially during its stronger period, would be fine for a larger planet. But it’s also plausible that you could have less iron but with a greater spin rate to generate a stronger field. The Earth was about 8 hrs./ day, but the Moon slowed us.

A faster spin rate also provides greater centrifugal force (i.e. less net g), but only in the equitorial regions. This benefit decreases as to the cosine of the latitude for a sphere, but you won’t have a nice sphere with faster rpm, of course. But it would be fairly close.

And how fast can I make a huge planet spin without destroying all life on it? I've thought a lot about gravity too,I actually have more questions about that..I would actually like to have high-gravity, normal gravity and zero-gravity zones on the planet.. I don't know if that's possible.
Only fast spin will give a surface gravity gradient. It would take a very fast rpm for a massive planet to rip apart.
Jupiter‘s day is only 10 hours.

The reduction in gravity is found in the centrifugal force: F = R * omega^2, where omega is angular speed. So, double the speed (12 hr. day) and double the radius, you’ll have 8x more centrifugal force than we have on Earth for any given latitude. You might Google what that value would be to get a lower gravity, if needed.

Atop a mountain has both faster omega and greater R value, so less gravity, but this amount isn’t noticeable.

- I would actually like the entire planet to have the same, warm climate everywhere. Maybe a little at the peak of the highest mountain, but no more. Could a complex but stable rotation pattern that isn't like Earth's provide that, or is that impossible?
Keeping the pole perpendicular to the orbit will eliminate seasons, but the poles will be cold. A binary star system might help, perhaps, to eliminate cold regions, but I’m only guessing.

Also: I want the part of the atmosphere we can easily breathe and fly around in to be much thicker too, nothing close to the ~16 km we have on Earth, I need much more. Of course that will make the predictingS of weatherpatterns even more complicated, just like messing around with the rotation..
A more massive planet essentially guarantees a more massive atmosphere, assuming it’s in the habitable zone.
 
Sep 20, 2021
6
7
15
Thank you so much for your response! Your name means: 'sun'. I've got questions about stars and about light and color too! But I'm much less concerned about those questions, since the sun or suns won't be much different from our own. The moon is a completely different story though - but I'm getting carried away; I should not waste time talking to the scientist! ;)

I'm not sure I entirely understand the first part of your answer - the more formula's you use, the more trouble I have understanding you.. I'm really not familiar with this, although I understand these awful formula's are the best way to write down these things. My simple mind distills this out your words: radius equals gravity - which, I know, is not what you mean. I think I understand what you mean a little bit though.. But would this mean a Jupiter-sized Earth (with a radius rougly ten times larger) would have ~10 g for an earthling-human at it's surface? Also, do I understand correctly that if I want a sort of Earth-like planet with earthish gravity, the 'crust', the top layer that people live and build on will always be a fraction (in it's thickness) of the magmafest that is going on underneath? If we would slice this hypothetical Jupiter-sized Earth in half, and look at all the layers - the crust and atmosphere would always be a tiny part of it - is that correct?

I KNOW it is tricky to make this planet habitable, haha, that's why I've come here. I know Jupiter is a gas giant and probably doesn't have anything we could stand on, not even in it's core. I think I kind of understand why planets turn into gasgiants beyond a certain point because of their size, though not fully. Does this mean 'Jupitearth' has to be hollow? Since the 'rocky' part, the crust, would always be a fraction of the total mass, and the inside can't be like Earth's because it would collapse, possibly into a gas giant? I've been trying to come up with ways to decrease the density of course. If the majority of the rocks are porous, on a large scale as well as on a local level, and we fill those spaces with water and air, some density is gone - but not nearly enough to approach Earth-like gravity at the planet's surface, is that correct? Does this mean the Jupiter-sized Earth has to be hollow and has to have some sort of miracle alternative for an iron core floating in it's centre, to have a habitable surface? What would happen if we filled the hollow centre with water? A water core? I don't know what would make more sense, ice or steam there - but I'm hoping you might?

And if there can't be an iron core, inside this hollow giant - does that means vulcanism and plate tectonics are also out the window? I know our magnetic field goes way beyond our surface, far into space, but I would think a planet ten times Earth's size would need an equally 'oversized' magnetic field to have the same 'protection'. But if there is no iron core, there won't be a magnetic field either, right? Or is that not true? You connect rotation speed to Earth's magnetism, which makes me hopeful there is a possibility for a magnetic field for the super-Earth even if it doesn't have an iron core. Is that correct?

If I'm not misunderstanding you, considerable differences in gravity on the giant planet's surface are out of the question? Since that would imply major differences underneath the crust, asymmetry so to speak, that could not exist long-term without solving it's own imbalance into some sort of 'perfectly' spherical state that would then result in equal gravity everywhere on the surface?

I understand that the seasons would be gone if the super-Earth isn't tilted like Earth. But still, the poles would be cold - which is absolutely unacceptable, because of reasons ;) Multiple suns is indeed a solution, but I'm pretty sure I don't want that - if I'm understanding you correctly, that is. I've also thought about this possibility, but I think I need the sunlight to come from one place within this fictional solar system. You mentioned the moon slowing down our rotation speed, could a moon, or multiple moons, also affect/control the direction of the rotation on a super-Earth? What I mean is this: could multiple moons, in various different eliptical orbits around the planet, continuously change the direction of the rotation so that all places get equal sunlight? Probably ridiculous?

Finally, some good news: the atmosphere will be huge automatically! That's a relief. I was afraid there was going to be some sort of insurmountable limit I wasn't aware of. The birds thank you sincerely! ;)

The planet that I'm trying to build doesn't really have oceans like we do, very little surfacewater compared to us actually. The total amount of water on the planet would be much higher than the total amount on Earth, of course, but it wouldn't dominate the surface like it does on our planet. And indeed, that does give me more space - but honestly that was a fortunate side effect of some other decisions I've made about the planet's biology ;)
 
  • Like
Reactions: Catastrophe

Catastrophe

The devil is in the detail
Sorry, I was under the misunderstanding that you wanted to increase the population, without increasing the mass proportionately. Other than population mass, of course.

Cat :)
 
Jun 1, 2020
1,694
1,445
3,560
.. But would this mean a Jupiter-sized Earth (with a radius rougly ten times larger) would have ~10 g for an earthling-human at it's surface?
Yes, but only if the densities were the same. They’re not. Jupiter is ~ 1/4 as dense as Earth, so it has 1/4 the mass it would’ve had if it had our density. Thus the gravity will be about 1/4 as much. (~ 2.5g)

Also, do I understand correctly that if I want a sort of Earth-like planet with earthish gravity, the 'crust', the top layer that people live and build on will always be a fraction (in it's thickness) of the magmafest that is going on underneath? If we would slice this hypothetical Jupiter-sized Earth in half, and look at all the layers - the crust and atmosphere would always be a tiny part of it - is that correct?
I’m no expert, but a thicker crust, if desired, is plausible if the planet formed with more lighter elements, which float upward during its hot formation. Or, if the planet is very old, the crust thickens as it cools. This, however, creates other issues like weaker tectonics and an older star.

I KNOW it is tricky to make this planet habitable, haha, that's why I've come here. I know Jupiter is a gas giant and probably doesn't have anything we could stand on, not even in it's core. I think I kind of understand why planets turn into gasgiants beyond a certain point because of their size, though not fully. Does this mean 'Jupitearth' has to be hollow?
The above shows how important density is. But I don’t see how one can have far less density for larger terrestrial planets. Lighter elements and a smaller, but faster spinning, iron core only help a little. The core is actually small in volume, btw.

Since the 'rocky' part, the crust, would always be a fraction of the total mass, and the inside can't be like Earth's because it would collapse, possibly into a gas giant?0
The star (temp.) determines planet types. Near the star, temperatures are hotter, so gases and many liquids will boil away. But each type of star has a frost line distance where gases are cool enough to not reach escape velocity. This allows rapid growth of large planets. 90% of every element is hydrogen, helium is almost the other 10%. Jupiter and Saturn are cool enough and massive enough to hold these, making them even larger planets.

Migration of planets is not trivial, so with imagination, planets might be able to go where you want them, but temperature changes must be kept in mind.

I've been trying to come up with ways to decrease the density of course. If the majority of the rocks are porous, on a large scale as well as on a local level, and we fill those spaces with water and air, some density is gone - but not nearly enough to approach Earth-like gravity at the planet's surface, is that correct? Does this mean the Jupiter-sized Earth has to be hollow and has to have some sort of miracle alternative for an iron core floating in it's centre, to have a habitable surface? What would happen if we filled the hollow centre with water? A water core? I don't know what would make more sense, ice or steam there - but I'm hoping you might?
. Planet formation temperatures due to impact (KE) make them molten. Hard to dodge this issue. Only smaller bodies might have watery cores (e.g. Europa).

I’ve no idea how a massive planet would become hollow.

The first planets to form in the cosmos should be far less dense since there were far fewer heavy elements then, I think. Water would have been abundant since stars make a lot of C, O.

And if there can't be an iron core, inside this hollow giant - does that means vulcanism and plate tectonics are also out the window?
. You need heat rising up to stir the crust. Water helps lubricate these flows. Earth has two forms of heat transfer from below: radioactivity and convection.

You’ll need very heavy elements for the first, so the early-aged planet idea won’t be that plausible if radioactivity is used. [well, you could toss in some extra SN to fix this, I suppose :)] Convection moves heat upward faster. A young planet will have a hotter core and likely more convection through all the fluid layers. So, perhaps a relatively young planet on the outer edge of the hab. zone might work since internal hear transfer would offset reduced star heating. A heavy atmosphere will likely hold temp. as well, so your larger planet would help here.

I know our magnetic field goes way beyond our surface, far into space, but I would think a planet ten times Earth's size would need an equally 'oversized' magnetic field to have the same 'protection'. But if there is no iron core, there won't be a magnetic field either, right? Or is that not true? You connect rotation speed to Earth's magnetism, which makes me hopeful there is a possibility for a magnetic field for the super-Earth even if it doesn't have an iron core. Is that correct?
The star flares, etc., won‘t be worse if the planet radius is larger, so maybe only a little more EM field is needed. You should have an iron core, but if it’s spinning faster it will produce more field strength. Thus allowing a little less density.

If I'm not misunderstanding you, considerable differences in gravity on the giant planet's surface are out of the question? Since that would imply major differences underneath the crust, asymmetry so to speak, that could not exist long-term without solving it's own imbalance into some sort of 'perfectly' spherical state that would then result in equal gravity everywhere on the surface?
Correct, unless it is spinning fast thus someone on the equator would be traveling in a circle at several thousand miles per hour, so gravity effect is a little less. But those at the poles are not, plus there would be bulge in the radius at the equator that also lowers surf. gravity. But the opposite is true at the pole. The equations can give you those differences.

I understand that the seasons would be gone if the super-Earth isn't tilted like Earth. But still, the poles would be cold - which is absolutely unacceptable, because of reasons ;) Multiple suns is indeed a solution, but I'm pretty sure I don't want that - if I'm understanding you correctly, that is. I've also thought about this possibility, but I think I need the sunlight to come from one place within this fictional solar system. You mentioned the moon slowing down our rotation speed, could a moon, or multiple moons, also affect/control the direction of the rotation on a super-Earth? What I mean is this: could multiple moons, in various different eliptical orbits around the planet, continuously change the direction of the rotation so that all places get equal sunlight? Probably ridiculous?
. Large moons are formed from impacts, apparently, so they aren’t captured. A large moon stabilizes the planets inclination (tilt). Small or no moons allow planets to change inclination. Think of a wobbling top as it spins down. Earth never wobbles more than about 25 deg., but Mars is more extreme due to the lack of a large moon.

But wobbles take eons. Earth takes ~26,000 years.

Finally, some good news: the atmosphere will be huge automatically! That's a relief. I was afraid there was going to be some sort of insurmountable limit I wasn't aware of. The birds thank you sincerely! ;)
. All nice questions that make me think. I‘m not sure all that I’ve said is correct, but I’ve enjoyed trying.
 
Last edited:

Catastrophe

The devil is in the detail
Koala, you posted "But I need much more space. "

What exactly is wrong with having a larger radius and having it comparatively hollow? That would give you much more space for many more people. Start with the planet as it is and build the equivalent of city skyscrapers - the whole city miles high? You can also use the volume for synthetic food production and other purposes.

Cat :)
 
Nov 2, 2020
232
194
260
In my opinion, a planet as big as our gas giants can't exist, or at least it would be made of gas.
We know that the lower a layer, the bigger the pressure, so, if such a planet exists, the pressure inside would be unimaginable.
Even if we allow the possibility to find deep inside light materials, we automatically have to exclude the possibility to find heavy materials on the surface. And what's more, without heavy materials the chances of finding an advanced society like ours, for instance, wouldn't be possible, anyway this doesn't exclude the possibility to find beings as "clever" as us.
Maybe if we lighten the core, we have the best result, cause a hollow planet, IMHO, is impossible to imagine.
 
  • Like
Reactions: Catastrophe

Catastrophe

The devil is in the detail
OP (#1) states "After doing a little research, I found why Earth-like planets can only be ~3,5 times bigger."

Google gives "Gas giants are large planets that contain more than 10 times the mass of Earth, they are also known as the Jovian or Outer Planets.
Neptune has "17 times as much mass compared to the Earth" and Uranus "more than 14.5 times as massive as our rocky home".

I am proposing larger radius but more hollow, to create living space for increased population, not vastly greater mass.

Cat :)
 
Jul 27, 2021
170
124
260
Careful and effective data combined together with cooperation show that it is possible to get more data with the facilities that we already have functioning.

Good example demonstrated by scientists is WASP-127b ('a hot Saturn' that orbits a Sun-like star located about 525 light-years away).

As a result, the planet’s atmosphere has expanded (or puffed up) to the point that it is 1.3 times as large as Jupiter but far less dense.’

Combined data from space and earth observations detected clouds in its upper atmosphere and measured their altitudes with high precision as never before.



The exoplanets investigation seems to become more clear, precise, unveiled and 'popular' very soon.
 
Jun 1, 2020
1,694
1,445
3,560
As a result, the planet’s atmosphere has expanded (or puffed up) to the point that it is 1.3 times as large as Jupiter but far less dense.’
Yes. It is very, very close to the star (0.048 AU), so the intense heat did the "puffing".

Without extra heat, you won't find planets appreciably larger than Jupiter because, interestingly, the more mass you give them in their development (or otherwise) the more they both grow and shrink at the same time. The shrinking is due to the extra gravity and it, essentially, matches any growth in radius.
 
May 14, 2021
207
147
260
Typically, brown dwarfs have more mass than Jupiter, but the size is not that much more, if any. The smallest red dwarf stars are also in the Jupiter size range or a bit more. Seems like Jupiter size or so is a size limit until it gets to be a bigger star.
 
Nov 2, 2020
232
194
260
Google gives "Gas giants are large planets that contain more than 10 times the mass of Earth, they are also known as the Jovian or Outer Planets.
Neptune has "17 times as much mass compared to the Earth" and Uranus "more than 14.5 times as massive as our rocky home".
Thanks for the information Cat! I dind't know there was a proper distinction between rocky planets and the giant ones.
I am proposing larger radius but more hollow, to create living space for increased population, not vastly greater mass.
In this case, if we lenghtened the radius of our planet without changing the mass of it, according to the general formula "F=Gm1m2/d2"; where G is the constant, m1 and m2 are the masses of the objects and d is the distance squared; the Force of Gravity would decrease. So, in this case we can actually do this!
The only problem is that of geology. I'm not a geologist though, so I don't know so much about this. Anyway, I think we can't leave uncovered spaces between the layers of our planet(?)
Correct me if I'm wrong, I'm not an expert...
 
  • Like
Reactions: Catastrophe

Catastrophe

The devil is in the detail
Vincen,
The gas giants are beyond the frost line (it is also known by similar names), beyond which hydrogen and helium can be retained. The terrestrial planets (Mercury, Venus, Earth, Mars) are inside this line (closer to the Sun) and the Sun's heat and solar wind have driven away the light gases.
Beyond the Asteroid Belt, the light gases (H and He) are retained and, since there was a lot of them, these contribute to the large masses of the gas giants and ice giants.

What I was suggesting for increasing radius, was to use surface materials to built upwards, so mass did not change, but living volume increased to house larger population. There could be gaps left between. It could be like skyscrapers covering large areas. Geologically, this would depend on the nature of the planet. This could be at the discretion of the author. It might be rich in aluminium to make a framework to contain silicate packing, or you could use large bricks, perhaps 6' x 1' x 3".5 (2m x 1m x 0.1m). Or just some suitable material invented for that planet.

Cat :)
 
  • Like
Reactions: vincenzosassone
Nov 2, 2020
232
194
260
Vincen,
The gas giants are beyond the frost line (it is also known by similar names), beyond which hydrogen and helium can be retained. The terrestrial planets (Mercury, Venus, Earth, Mars) are inside this line (closer to the Sun) and the Sun's heat and solar wind have driven away the light gases.
Beyond the Asteroid Belt, the light gases (H and He) are retained and, since there was a lot of them, these contribute to the large masses of the gas giants and ice giants.
Thank you Cat for the explanation!
What I was suggesting for increasing radius, was to use surface materials to built upwards, so mass did not change, but living volume increased to house larger population. There could be gaps left between. It could be like skyscrapers covering large areas. Geologically, this would depend on the nature of the planet. This could be at the discretion of the author. It might be rich in aluminium to make a framework to contain silicate packing, or you could use large bricks, perhaps 6' x 1' x 3".5 (2m x 1m x 0.1m). Or just some suitable material invented for that planet.
I'm sorry for the previous misunderstanding, this is brilliant.
 
  • Like
Reactions: Catastrophe

ASK THE COMMUNITY