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How can Ganymede have an Earth-like gravity without us having realized it?
Clash Royale CLAN TAG#URR8PPP
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Imagine a small primitive humanoid civilization that developed independently in caves under the surface of Ganymede. We can assume there's enough light that filters through the crystalline surface to support life, and that there's enough air trapped in these caves for them to breathe.
But let's say these people also happen have a gravity that's slightly greater than Earth's. How could that be the case? And why wouldn't Earth's astronomers have discovered that before now?
Also, are there any other significant factors that would make it difficult for Earth-like life to thrive? Things that would be harder to hand-wave away?
(The SF here is about as hard as cotton candy, so answers don't need to be completely realistic. I'd just like to avoid directly contradicting known observations any more than I need to.)
science-based science-fiction environment earth-like moons
asked 2 hours ago
Admiral Jota
113
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add a comment |Â
up vote
2
down vote
favorite
Imagine a small primitive humanoid civilization that developed independently in caves under the surface of Ganymede. We can assume there's enough light that filters through the crystalline surface to support life, and that there's enough air trapped in these caves for them to breathe.
But let's say these people also happen have a gravity that's slightly greater than Earth's. How could that be the case? And why wouldn't Earth's astronomers have discovered that before now?
Also, are there any other significant factors that would make it difficult for Earth-like life to thrive? Things that would be harder to hand-wave away?
(The SF here is about as hard as cotton candy, so answers don't need to be completely realistic. I'd just like to avoid directly contradicting known observations any more than I need to.)
science-based science-fiction environment earth-like moons
asked 2 hours ago
Admiral Jota
113
New contributor
Admiral Jota is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Welcome to Worldbuilding. Please take the tour and visit the help center. Can you add a tag explaining which kind of answer are you looking for? Science based or magic?
– L.Dutch♦
2 hours ago
Thanks. I added the science-based tag, and I'm checking out the tour right now.
– Admiral Jota
2 hours ago
1
Are there aliens or Q involved? Gravity is linked to mass, and both govern orbital characteristics, so unless there is some external force at play, gravity is set for Ganymede. Also, did life evolve there, or was it seeded? Because humans are not inevitable as a product of evolution...
– bukwyrm
1 hour ago
I'm pretty flexible on the ultimate origins of life there. I could happily go with an "ancient aliens seeded both Earth and Ganymede billions of years ago" theory if that makes things easier. And I'd be fine with suggesting those ancient aliens used some unknown advanced technology or "impossible" materials to intentionally craft an ideal environment there.
– Admiral Jota
1 hour ago
Another thought: I don't necessarily need the entire moon to have a high gravity. I only need a high-gravity environment that's large enough for a small underground civilization. Spinning an entire cave system seems rather unrealistic, but perhaps there are other good pseudo-gravity options? Or could I have a single highly dense point that produced high G's in a small area that dropped off substantially with distance?
– Admiral Jota
1 hour ago
add a comment |Â
up vote
2
down vote
favorite
up vote
2
down vote
favorite
Imagine a small primitive humanoid civilization that developed independently in caves under the surface of Ganymede. We can assume there's enough light that filters through the crystalline surface to support life, and that there's enough air trapped in these caves for them to breathe.
But let's say these people also happen have a gravity that's slightly greater than Earth's. How could that be the case? And why wouldn't Earth's astronomers have discovered that before now?
Also, are there any other significant factors that would make it difficult for Earth-like life to thrive? Things that would be harder to hand-wave away?
(The SF here is about as hard as cotton candy, so answers don't need to be completely realistic. I'd just like to avoid directly contradicting known observations any more than I need to.)
science-based science-fiction environment earth-like moons
asked 2 hours ago
Admiral Jota
113
New contributor
Admiral Jota is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Imagine a small primitive humanoid civilization that developed independently in caves under the surface of Ganymede. We can assume there's enough light that filters through the crystalline surface to support life, and that there's enough air trapped in these caves for them to breathe.
But let's say these people also happen have a gravity that's slightly greater than Earth's. How could that be the case? And why wouldn't Earth's astronomers have discovered that before now?
Also, are there any other significant factors that would make it difficult for Earth-like life to thrive? Things that would be harder to hand-wave away?
(The SF here is about as hard as cotton candy, so answers don't need to be completely realistic. I'd just like to avoid directly contradicting known observations any more than I need to.)
science-based science-fiction environment earth-like moons
science-based science-fiction environment earth-like moons
asked 2 hours ago
Admiral Jota
113
New contributor
Admiral Jota is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 2 hours ago
Admiral Jota
113
New contributor
Admiral Jota is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 2 hours ago
asked 2 hours ago
Admiral Jota
113
New contributor
Admiral Jota is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 2 hours ago
Admiral Jota
113
asked 2 hours ago
Admiral Jota
113
113
New contributor
Admiral Jota is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Admiral Jota is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Admiral Jota is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Welcome to Worldbuilding. Please take the tour and visit the help center. Can you add a tag explaining which kind of answer are you looking for? Science based or magic?
– L.Dutch♦
2 hours ago
Thanks. I added the science-based tag, and I'm checking out the tour right now.
– Admiral Jota
2 hours ago
1
Are there aliens or Q involved? Gravity is linked to mass, and both govern orbital characteristics, so unless there is some external force at play, gravity is set for Ganymede. Also, did life evolve there, or was it seeded? Because humans are not inevitable as a product of evolution...
– bukwyrm
1 hour ago
I'm pretty flexible on the ultimate origins of life there. I could happily go with an "ancient aliens seeded both Earth and Ganymede billions of years ago" theory if that makes things easier. And I'd be fine with suggesting those ancient aliens used some unknown advanced technology or "impossible" materials to intentionally craft an ideal environment there.
– Admiral Jota
1 hour ago
Another thought: I don't necessarily need the entire moon to have a high gravity. I only need a high-gravity environment that's large enough for a small underground civilization. Spinning an entire cave system seems rather unrealistic, but perhaps there are other good pseudo-gravity options? Or could I have a single highly dense point that produced high G's in a small area that dropped off substantially with distance?
– Admiral Jota
1 hour ago
add a comment |Â
Welcome to Worldbuilding. Please take the tour and visit the help center. Can you add a tag explaining which kind of answer are you looking for? Science based or magic?
– L.Dutch♦
2 hours ago
Thanks. I added the science-based tag, and I'm checking out the tour right now.
– Admiral Jota
2 hours ago
1
Are there aliens or Q involved? Gravity is linked to mass, and both govern orbital characteristics, so unless there is some external force at play, gravity is set for Ganymede. Also, did life evolve there, or was it seeded? Because humans are not inevitable as a product of evolution...
– bukwyrm
1 hour ago
I'm pretty flexible on the ultimate origins of life there. I could happily go with an "ancient aliens seeded both Earth and Ganymede billions of years ago" theory if that makes things easier. And I'd be fine with suggesting those ancient aliens used some unknown advanced technology or "impossible" materials to intentionally craft an ideal environment there.
– Admiral Jota
1 hour ago
Another thought: I don't necessarily need the entire moon to have a high gravity. I only need a high-gravity environment that's large enough for a small underground civilization. Spinning an entire cave system seems rather unrealistic, but perhaps there are other good pseudo-gravity options? Or could I have a single highly dense point that produced high G's in a small area that dropped off substantially with distance?
– Admiral Jota
1 hour ago
Welcome to Worldbuilding. Please take the tour and visit the help center. Can you add a tag explaining which kind of answer are you looking for? Science based or magic?
– L.Dutch♦
2 hours ago
Welcome to Worldbuilding. Please take the tour and visit the help center. Can you add a tag explaining which kind of answer are you looking for? Science based or magic?
– L.Dutch♦
2 hours ago
Thanks. I added the science-based tag, and I'm checking out the tour right now.
– Admiral Jota
2 hours ago
Thanks. I added the science-based tag, and I'm checking out the tour right now.
– Admiral Jota
2 hours ago
1
1
Are there aliens or Q involved? Gravity is linked to mass, and both govern orbital characteristics, so unless there is some external force at play, gravity is set for Ganymede. Also, did life evolve there, or was it seeded? Because humans are not inevitable as a product of evolution...
– bukwyrm
1 hour ago
Are there aliens or Q involved? Gravity is linked to mass, and both govern orbital characteristics, so unless there is some external force at play, gravity is set for Ganymede. Also, did life evolve there, or was it seeded? Because humans are not inevitable as a product of evolution...
– bukwyrm
1 hour ago
I'm pretty flexible on the ultimate origins of life there. I could happily go with an "ancient aliens seeded both Earth and Ganymede billions of years ago" theory if that makes things easier. And I'd be fine with suggesting those ancient aliens used some unknown advanced technology or "impossible" materials to intentionally craft an ideal environment there.
– Admiral Jota
1 hour ago
I'm pretty flexible on the ultimate origins of life there. I could happily go with an "ancient aliens seeded both Earth and Ganymede billions of years ago" theory if that makes things easier. And I'd be fine with suggesting those ancient aliens used some unknown advanced technology or "impossible" materials to intentionally craft an ideal environment there.
– Admiral Jota
1 hour ago
Another thought: I don't necessarily need the entire moon to have a high gravity. I only need a high-gravity environment that's large enough for a small underground civilization. Spinning an entire cave system seems rather unrealistic, but perhaps there are other good pseudo-gravity options? Or could I have a single highly dense point that produced high G's in a small area that dropped off substantially with distance?
– Admiral Jota
1 hour ago
Another thought: I don't necessarily need the entire moon to have a high gravity. I only need a high-gravity environment that's large enough for a small underground civilization. Spinning an entire cave system seems rather unrealistic, but perhaps there are other good pseudo-gravity options? Or could I have a single highly dense point that produced high G's in a small area that dropped off substantially with distance?
– Admiral Jota
1 hour ago
add a comment |Â
4 Answers
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up vote
4
down vote
I'm sorry, but it's impossible.
Ganymede has 2.4% of Earth's mass. That mass is what generates gravity.
If it had more gravity then it would distort the orbits of the other moons and we would know about it. We know the mass of every substantial body in the solar system (and in fact some of them were detected because they were distorting the orbits of things we did know about and we were able to go look in the right place).
http://solarviews.com/eng/ganymede.htm
You need to come up with a way to achieve your goals that does not involve gravity as we know it. For example clawed feet to grasp the ice, magnetic boots, or even just bouncing around in ice tunnels are all possible.
answered 1 hour ago
Tim B♦
55.2k22154270
add a comment |Â
up vote
2
down vote
Let's back track and figure out how we know the mass/gravitaty on Ganymedes. (Longer read here).
First off, we need to calculate the radius of the Earth. This has been known to a relatively accurate number for a very long time. Then we need to measure what Earth's 'gravitational pull', or mass, is, by using an object of a known mass. With this in hand, we can actually calculate the mass of the sun knowing its distance to Earth (again, science has proven this).
From here we can measure the mass of any planet in our solar system with relative ease. With Jupiter's mass now known, we can actually watch Ganymedes and calculate it's mass as well.
At any point, if there was an error (and rest assured, there isn't one large enough to accomplish what you request), it would affect our measurements of everything down that linked chain. So in your case, we'd have to have had grossly mismeasured either Jupiter's orbital movements, or Ganymedes (or likely both to get the increase in mass you need).
Suffice it to say, this is highly unlikely.
On to your other question, check out the amount of radiation on Ganymedes. At 8 rem a day, it is definitely going to be wrecking havoc on your earth-like life over time.
answered 1 hour ago
ColonelPanic
1,46919
add a comment |Â
up vote
2
down vote
Don't change the mass - change the density.
(Soft science ahead - all hands brace for impact!)
One thing you probably shouldn't do is change Ganymede's mass. That would change its orbit (and its influence on the other moons) in unavoidable and easily observable ways. You'd have to do some elaborate hand-waving to make Ganymede appear to be its apparent mass while having a very different actual mass.
To have a solution from changing the density will still require some hand-waving, but maybe it's allowable in a "cotton-candy-scifi" universe...you can be the judge of that!
To attain earth-like gravity in your caves, we would have to: 1) make Ganymede's core unnaturally dense and its mantle is unnaturally light, and 2) place your caves much closer to the core. The handwaving required to make this happen is two-fold:
Firstly, to actually concentrate Ganymede's mass this much in the core, you could not use any naturally occurring material in the known universe. Materials made of conventional elements are too light, and electron- or neutron-degenerate matter would not remain compressed under earthlike gravity--it would explode. So...probably the best soft-sci-fi solution (without invoking artificial gravity generators) is that Ganymede's core contains degenerate matter which for some reason can't decompress. (Is it special matter? Is it in a fluke, naturally occurring statis field? Handwave!) Similarly, you'll need to handwave a material to compose Ganymede's mantle that is extremely light and somehow looks to our telescopes like a salty ocean. (See https://en.wikipedia.org/wiki/Ganymede_(moon)#Composition ) Which bring us to our next point...
We will need to handwave some of our observations of Ganymede's physical appearance and its moment of inertia factor ( https://en.wikipedia.org/wiki/Moment_of_inertia_factor ). To be honest, I don't think there will be any self-consistent and elegant way to explain away all of the observations we've made of it. But at the very least, try to have a reason for why Ganymede's surface is or appears to be made up of water ice and silicate rock, and why it appears to have a subsurface salty ocean and an iron-rich core.
(To tackle the surface, I would offer this...our extremely light mantle-material is somehow also fairly tough and rigid, and the silicate rock of the surface is mostly layers of dust/fragments from meteor impacts.)
answered 1 hour ago
Qami
1,324214
Thanks -- this looks very promising! Good food for thought about the exotic materials and physical appearance. (I'll upvote you as soon as I have enough rep to do so.)
– Admiral Jota
1 hour ago
You could use a black hole. Even denser then degenerate matter, stable (until it decays) and exists in real life!
– 0something0
45 mins ago
Yes, I've been thinking about it a bit more since I wrote my answer and a black hole which the people live near was the only thing I could come up with that is even slightly viable - and even that has enough problems to put it firmly in the realm of cotton candy science)
– Tim B♦
26 mins ago
Small black holes decay fast, and shell theorem makes it unbelievable that it will stay at the center.
– Mołot
25 mins ago
add a comment |Â
up vote
1
down vote
This could not happen.
Knowing what we know of Earth, Ganymede, and Jupiter, the gravitational attraction between Jupiter and Ganymede is 1.637795249×10²²N. If we were to simply substitute Earth in place of Ganymede at the same orbital distance the gravitational attraction would be 6.60066078×10²³N. An Earth-mass object would have to orbit much faster (2.4x??) in order to compensate for the greatly increased gravitational attraction.
We know the mass of Ganymede because of its distance from Jupiter and its orbital speed.
So, no, you have to break physics to make this work.
answered 1 hour ago
Ian Moote
66419
add a comment |Â
4 Answers
4
active
oldest
votes
4 Answers
4
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
4
down vote
I'm sorry, but it's impossible.
Ganymede has 2.4% of Earth's mass. That mass is what generates gravity.
If it had more gravity then it would distort the orbits of the other moons and we would know about it. We know the mass of every substantial body in the solar system (and in fact some of them were detected because they were distorting the orbits of things we did know about and we were able to go look in the right place).
http://solarviews.com/eng/ganymede.htm
You need to come up with a way to achieve your goals that does not involve gravity as we know it. For example clawed feet to grasp the ice, magnetic boots, or even just bouncing around in ice tunnels are all possible.
answered 1 hour ago
Tim B♦
55.2k22154270
add a comment |Â
up vote
4
down vote
I'm sorry, but it's impossible.
Ganymede has 2.4% of Earth's mass. That mass is what generates gravity.
If it had more gravity then it would distort the orbits of the other moons and we would know about it. We know the mass of every substantial body in the solar system (and in fact some of them were detected because they were distorting the orbits of things we did know about and we were able to go look in the right place).
http://solarviews.com/eng/ganymede.htm
You need to come up with a way to achieve your goals that does not involve gravity as we know it. For example clawed feet to grasp the ice, magnetic boots, or even just bouncing around in ice tunnels are all possible.
answered 1 hour ago
Tim B♦
55.2k22154270
add a comment |Â
up vote
4
down vote
up vote
4
down vote
I'm sorry, but it's impossible.
Ganymede has 2.4% of Earth's mass. That mass is what generates gravity.
If it had more gravity then it would distort the orbits of the other moons and we would know about it. We know the mass of every substantial body in the solar system (and in fact some of them were detected because they were distorting the orbits of things we did know about and we were able to go look in the right place).
http://solarviews.com/eng/ganymede.htm
You need to come up with a way to achieve your goals that does not involve gravity as we know it. For example clawed feet to grasp the ice, magnetic boots, or even just bouncing around in ice tunnels are all possible.
answered 1 hour ago
Tim B♦
55.2k22154270
I'm sorry, but it's impossible.
Ganymede has 2.4% of Earth's mass. That mass is what generates gravity.
If it had more gravity then it would distort the orbits of the other moons and we would know about it. We know the mass of every substantial body in the solar system (and in fact some of them were detected because they were distorting the orbits of things we did know about and we were able to go look in the right place).
http://solarviews.com/eng/ganymede.htm
You need to come up with a way to achieve your goals that does not involve gravity as we know it. For example clawed feet to grasp the ice, magnetic boots, or even just bouncing around in ice tunnels are all possible.
answered 1 hour ago
Tim B♦
55.2k22154270
answered 1 hour ago
Tim B♦
55.2k22154270
answered 1 hour ago
Tim B♦
55.2k22154270
answered 1 hour ago
Tim B♦
55.2k22154270
55.2k22154270
add a comment |Â
add a comment |Â
up vote
2
down vote
Let's back track and figure out how we know the mass/gravitaty on Ganymedes. (Longer read here).
First off, we need to calculate the radius of the Earth. This has been known to a relatively accurate number for a very long time. Then we need to measure what Earth's 'gravitational pull', or mass, is, by using an object of a known mass. With this in hand, we can actually calculate the mass of the sun knowing its distance to Earth (again, science has proven this).
From here we can measure the mass of any planet in our solar system with relative ease. With Jupiter's mass now known, we can actually watch Ganymedes and calculate it's mass as well.
At any point, if there was an error (and rest assured, there isn't one large enough to accomplish what you request), it would affect our measurements of everything down that linked chain. So in your case, we'd have to have had grossly mismeasured either Jupiter's orbital movements, or Ganymedes (or likely both to get the increase in mass you need).
Suffice it to say, this is highly unlikely.
On to your other question, check out the amount of radiation on Ganymedes. At 8 rem a day, it is definitely going to be wrecking havoc on your earth-like life over time.
answered 1 hour ago
ColonelPanic
1,46919
add a comment |Â
up vote
2
down vote
Let's back track and figure out how we know the mass/gravitaty on Ganymedes. (Longer read here).
First off, we need to calculate the radius of the Earth. This has been known to a relatively accurate number for a very long time. Then we need to measure what Earth's 'gravitational pull', or mass, is, by using an object of a known mass. With this in hand, we can actually calculate the mass of the sun knowing its distance to Earth (again, science has proven this).
From here we can measure the mass of any planet in our solar system with relative ease. With Jupiter's mass now known, we can actually watch Ganymedes and calculate it's mass as well.
At any point, if there was an error (and rest assured, there isn't one large enough to accomplish what you request), it would affect our measurements of everything down that linked chain. So in your case, we'd have to have had grossly mismeasured either Jupiter's orbital movements, or Ganymedes (or likely both to get the increase in mass you need).
Suffice it to say, this is highly unlikely.
On to your other question, check out the amount of radiation on Ganymedes. At 8 rem a day, it is definitely going to be wrecking havoc on your earth-like life over time.
answered 1 hour ago
ColonelPanic
1,46919
add a comment |Â
up vote
2
down vote
up vote
2
down vote
Let's back track and figure out how we know the mass/gravitaty on Ganymedes. (Longer read here).
First off, we need to calculate the radius of the Earth. This has been known to a relatively accurate number for a very long time. Then we need to measure what Earth's 'gravitational pull', or mass, is, by using an object of a known mass. With this in hand, we can actually calculate the mass of the sun knowing its distance to Earth (again, science has proven this).
From here we can measure the mass of any planet in our solar system with relative ease. With Jupiter's mass now known, we can actually watch Ganymedes and calculate it's mass as well.
At any point, if there was an error (and rest assured, there isn't one large enough to accomplish what you request), it would affect our measurements of everything down that linked chain. So in your case, we'd have to have had grossly mismeasured either Jupiter's orbital movements, or Ganymedes (or likely both to get the increase in mass you need).
Suffice it to say, this is highly unlikely.
On to your other question, check out the amount of radiation on Ganymedes. At 8 rem a day, it is definitely going to be wrecking havoc on your earth-like life over time.
answered 1 hour ago
ColonelPanic
1,46919
Let's back track and figure out how we know the mass/gravitaty on Ganymedes. (Longer read here).
First off, we need to calculate the radius of the Earth. This has been known to a relatively accurate number for a very long time. Then we need to measure what Earth's 'gravitational pull', or mass, is, by using an object of a known mass. With this in hand, we can actually calculate the mass of the sun knowing its distance to Earth (again, science has proven this).
From here we can measure the mass of any planet in our solar system with relative ease. With Jupiter's mass now known, we can actually watch Ganymedes and calculate it's mass as well.
At any point, if there was an error (and rest assured, there isn't one large enough to accomplish what you request), it would affect our measurements of everything down that linked chain. So in your case, we'd have to have had grossly mismeasured either Jupiter's orbital movements, or Ganymedes (or likely both to get the increase in mass you need).
Suffice it to say, this is highly unlikely.
On to your other question, check out the amount of radiation on Ganymedes. At 8 rem a day, it is definitely going to be wrecking havoc on your earth-like life over time.
answered 1 hour ago
ColonelPanic
1,46919
answered 1 hour ago
ColonelPanic
1,46919
answered 1 hour ago
ColonelPanic
1,46919
answered 1 hour ago
ColonelPanic
1,46919
1,46919
add a comment |Â
add a comment |Â
up vote
2
down vote
Don't change the mass - change the density.
(Soft science ahead - all hands brace for impact!)
One thing you probably shouldn't do is change Ganymede's mass. That would change its orbit (and its influence on the other moons) in unavoidable and easily observable ways. You'd have to do some elaborate hand-waving to make Ganymede appear to be its apparent mass while having a very different actual mass.
To have a solution from changing the density will still require some hand-waving, but maybe it's allowable in a "cotton-candy-scifi" universe...you can be the judge of that!
To attain earth-like gravity in your caves, we would have to: 1) make Ganymede's core unnaturally dense and its mantle is unnaturally light, and 2) place your caves much closer to the core. The handwaving required to make this happen is two-fold:
Firstly, to actually concentrate Ganymede's mass this much in the core, you could not use any naturally occurring material in the known universe. Materials made of conventional elements are too light, and electron- or neutron-degenerate matter would not remain compressed under earthlike gravity--it would explode. So...probably the best soft-sci-fi solution (without invoking artificial gravity generators) is that Ganymede's core contains degenerate matter which for some reason can't decompress. (Is it special matter? Is it in a fluke, naturally occurring statis field? Handwave!) Similarly, you'll need to handwave a material to compose Ganymede's mantle that is extremely light and somehow looks to our telescopes like a salty ocean. (See https://en.wikipedia.org/wiki/Ganymede_(moon)#Composition ) Which bring us to our next point...
We will need to handwave some of our observations of Ganymede's physical appearance and its moment of inertia factor ( https://en.wikipedia.org/wiki/Moment_of_inertia_factor ). To be honest, I don't think there will be any self-consistent and elegant way to explain away all of the observations we've made of it. But at the very least, try to have a reason for why Ganymede's surface is or appears to be made up of water ice and silicate rock, and why it appears to have a subsurface salty ocean and an iron-rich core.
(To tackle the surface, I would offer this...our extremely light mantle-material is somehow also fairly tough and rigid, and the silicate rock of the surface is mostly layers of dust/fragments from meteor impacts.)
answered 1 hour ago
Qami
1,324214
Thanks -- this looks very promising! Good food for thought about the exotic materials and physical appearance. (I'll upvote you as soon as I have enough rep to do so.)
– Admiral Jota
1 hour ago
You could use a black hole. Even denser then degenerate matter, stable (until it decays) and exists in real life!
– 0something0
45 mins ago
Yes, I've been thinking about it a bit more since I wrote my answer and a black hole which the people live near was the only thing I could come up with that is even slightly viable - and even that has enough problems to put it firmly in the realm of cotton candy science)
– Tim B♦
26 mins ago
Small black holes decay fast, and shell theorem makes it unbelievable that it will stay at the center.
– Mołot
25 mins ago
add a comment |Â
up vote
2
down vote
Don't change the mass - change the density.
(Soft science ahead - all hands brace for impact!)
One thing you probably shouldn't do is change Ganymede's mass. That would change its orbit (and its influence on the other moons) in unavoidable and easily observable ways. You'd have to do some elaborate hand-waving to make Ganymede appear to be its apparent mass while having a very different actual mass.
To have a solution from changing the density will still require some hand-waving, but maybe it's allowable in a "cotton-candy-scifi" universe...you can be the judge of that!
To attain earth-like gravity in your caves, we would have to: 1) make Ganymede's core unnaturally dense and its mantle is unnaturally light, and 2) place your caves much closer to the core. The handwaving required to make this happen is two-fold:
Firstly, to actually concentrate Ganymede's mass this much in the core, you could not use any naturally occurring material in the known universe. Materials made of conventional elements are too light, and electron- or neutron-degenerate matter would not remain compressed under earthlike gravity--it would explode. So...probably the best soft-sci-fi solution (without invoking artificial gravity generators) is that Ganymede's core contains degenerate matter which for some reason can't decompress. (Is it special matter? Is it in a fluke, naturally occurring statis field? Handwave!) Similarly, you'll need to handwave a material to compose Ganymede's mantle that is extremely light and somehow looks to our telescopes like a salty ocean. (See https://en.wikipedia.org/wiki/Ganymede_(moon)#Composition ) Which bring us to our next point...
We will need to handwave some of our observations of Ganymede's physical appearance and its moment of inertia factor ( https://en.wikipedia.org/wiki/Moment_of_inertia_factor ). To be honest, I don't think there will be any self-consistent and elegant way to explain away all of the observations we've made of it. But at the very least, try to have a reason for why Ganymede's surface is or appears to be made up of water ice and silicate rock, and why it appears to have a subsurface salty ocean and an iron-rich core.
(To tackle the surface, I would offer this...our extremely light mantle-material is somehow also fairly tough and rigid, and the silicate rock of the surface is mostly layers of dust/fragments from meteor impacts.)
answered 1 hour ago
Qami
1,324214
Thanks -- this looks very promising! Good food for thought about the exotic materials and physical appearance. (I'll upvote you as soon as I have enough rep to do so.)
– Admiral Jota
1 hour ago
You could use a black hole. Even denser then degenerate matter, stable (until it decays) and exists in real life!
– 0something0
45 mins ago
Yes, I've been thinking about it a bit more since I wrote my answer and a black hole which the people live near was the only thing I could come up with that is even slightly viable - and even that has enough problems to put it firmly in the realm of cotton candy science)
– Tim B♦
26 mins ago
Small black holes decay fast, and shell theorem makes it unbelievable that it will stay at the center.
– Mołot
25 mins ago
add a comment |Â
up vote
2
down vote
up vote
2
down vote
Don't change the mass - change the density.
(Soft science ahead - all hands brace for impact!)
One thing you probably shouldn't do is change Ganymede's mass. That would change its orbit (and its influence on the other moons) in unavoidable and easily observable ways. You'd have to do some elaborate hand-waving to make Ganymede appear to be its apparent mass while having a very different actual mass.
To have a solution from changing the density will still require some hand-waving, but maybe it's allowable in a "cotton-candy-scifi" universe...you can be the judge of that!
To attain earth-like gravity in your caves, we would have to: 1) make Ganymede's core unnaturally dense and its mantle is unnaturally light, and 2) place your caves much closer to the core. The handwaving required to make this happen is two-fold:
Firstly, to actually concentrate Ganymede's mass this much in the core, you could not use any naturally occurring material in the known universe. Materials made of conventional elements are too light, and electron- or neutron-degenerate matter would not remain compressed under earthlike gravity--it would explode. So...probably the best soft-sci-fi solution (without invoking artificial gravity generators) is that Ganymede's core contains degenerate matter which for some reason can't decompress. (Is it special matter? Is it in a fluke, naturally occurring statis field? Handwave!) Similarly, you'll need to handwave a material to compose Ganymede's mantle that is extremely light and somehow looks to our telescopes like a salty ocean. (See https://en.wikipedia.org/wiki/Ganymede_(moon)#Composition ) Which bring us to our next point...
We will need to handwave some of our observations of Ganymede's physical appearance and its moment of inertia factor ( https://en.wikipedia.org/wiki/Moment_of_inertia_factor ). To be honest, I don't think there will be any self-consistent and elegant way to explain away all of the observations we've made of it. But at the very least, try to have a reason for why Ganymede's surface is or appears to be made up of water ice and silicate rock, and why it appears to have a subsurface salty ocean and an iron-rich core.
(To tackle the surface, I would offer this...our extremely light mantle-material is somehow also fairly tough and rigid, and the silicate rock of the surface is mostly layers of dust/fragments from meteor impacts.)
answered 1 hour ago
Qami
1,324214
Don't change the mass - change the density.
(Soft science ahead - all hands brace for impact!)
One thing you probably shouldn't do is change Ganymede's mass. That would change its orbit (and its influence on the other moons) in unavoidable and easily observable ways. You'd have to do some elaborate hand-waving to make Ganymede appear to be its apparent mass while having a very different actual mass.
To have a solution from changing the density will still require some hand-waving, but maybe it's allowable in a "cotton-candy-scifi" universe...you can be the judge of that!
To attain earth-like gravity in your caves, we would have to: 1) make Ganymede's core unnaturally dense and its mantle is unnaturally light, and 2) place your caves much closer to the core. The handwaving required to make this happen is two-fold:
Firstly, to actually concentrate Ganymede's mass this much in the core, you could not use any naturally occurring material in the known universe. Materials made of conventional elements are too light, and electron- or neutron-degenerate matter would not remain compressed under earthlike gravity--it would explode. So...probably the best soft-sci-fi solution (without invoking artificial gravity generators) is that Ganymede's core contains degenerate matter which for some reason can't decompress. (Is it special matter? Is it in a fluke, naturally occurring statis field? Handwave!) Similarly, you'll need to handwave a material to compose Ganymede's mantle that is extremely light and somehow looks to our telescopes like a salty ocean. (See https://en.wikipedia.org/wiki/Ganymede_(moon)#Composition ) Which bring us to our next point...
We will need to handwave some of our observations of Ganymede's physical appearance and its moment of inertia factor ( https://en.wikipedia.org/wiki/Moment_of_inertia_factor ). To be honest, I don't think there will be any self-consistent and elegant way to explain away all of the observations we've made of it. But at the very least, try to have a reason for why Ganymede's surface is or appears to be made up of water ice and silicate rock, and why it appears to have a subsurface salty ocean and an iron-rich core.
(To tackle the surface, I would offer this...our extremely light mantle-material is somehow also fairly tough and rigid, and the silicate rock of the surface is mostly layers of dust/fragments from meteor impacts.)
answered 1 hour ago
Qami
1,324214
answered 1 hour ago
Qami
1,324214
answered 1 hour ago
Qami
1,324214
answered 1 hour ago
Qami
1,324214
1,324214
Thanks -- this looks very promising! Good food for thought about the exotic materials and physical appearance. (I'll upvote you as soon as I have enough rep to do so.)
– Admiral Jota
1 hour ago
You could use a black hole. Even denser then degenerate matter, stable (until it decays) and exists in real life!
– 0something0
45 mins ago
Yes, I've been thinking about it a bit more since I wrote my answer and a black hole which the people live near was the only thing I could come up with that is even slightly viable - and even that has enough problems to put it firmly in the realm of cotton candy science)
– Tim B♦
26 mins ago
Small black holes decay fast, and shell theorem makes it unbelievable that it will stay at the center.
– Mołot
25 mins ago
add a comment |Â
Thanks -- this looks very promising! Good food for thought about the exotic materials and physical appearance. (I'll upvote you as soon as I have enough rep to do so.)
– Admiral Jota
1 hour ago
You could use a black hole. Even denser then degenerate matter, stable (until it decays) and exists in real life!
– 0something0
45 mins ago
Yes, I've been thinking about it a bit more since I wrote my answer and a black hole which the people live near was the only thing I could come up with that is even slightly viable - and even that has enough problems to put it firmly in the realm of cotton candy science)
– Tim B♦
26 mins ago
Small black holes decay fast, and shell theorem makes it unbelievable that it will stay at the center.
– Mołot
25 mins ago
Thanks -- this looks very promising! Good food for thought about the exotic materials and physical appearance. (I'll upvote you as soon as I have enough rep to do so.)
– Admiral Jota
1 hour ago
Thanks -- this looks very promising! Good food for thought about the exotic materials and physical appearance. (I'll upvote you as soon as I have enough rep to do so.)
– Admiral Jota
1 hour ago
You could use a black hole. Even denser then degenerate matter, stable (until it decays) and exists in real life!
– 0something0
45 mins ago
You could use a black hole. Even denser then degenerate matter, stable (until it decays) and exists in real life!
– 0something0
45 mins ago
Yes, I've been thinking about it a bit more since I wrote my answer and a black hole which the people live near was the only thing I could come up with that is even slightly viable - and even that has enough problems to put it firmly in the realm of cotton candy science)
– Tim B♦
26 mins ago
Yes, I've been thinking about it a bit more since I wrote my answer and a black hole which the people live near was the only thing I could come up with that is even slightly viable - and even that has enough problems to put it firmly in the realm of cotton candy science)
– Tim B♦
26 mins ago
Small black holes decay fast, and shell theorem makes it unbelievable that it will stay at the center.
– Mołot
25 mins ago
Small black holes decay fast, and shell theorem makes it unbelievable that it will stay at the center.
– Mołot
25 mins ago
add a comment |Â
up vote
1
down vote
This could not happen.
Knowing what we know of Earth, Ganymede, and Jupiter, the gravitational attraction between Jupiter and Ganymede is 1.637795249×10²²N. If we were to simply substitute Earth in place of Ganymede at the same orbital distance the gravitational attraction would be 6.60066078×10²³N. An Earth-mass object would have to orbit much faster (2.4x??) in order to compensate for the greatly increased gravitational attraction.
We know the mass of Ganymede because of its distance from Jupiter and its orbital speed.
So, no, you have to break physics to make this work.
answered 1 hour ago
Ian Moote
66419
add a comment |Â
up vote
1
down vote
This could not happen.
Knowing what we know of Earth, Ganymede, and Jupiter, the gravitational attraction between Jupiter and Ganymede is 1.637795249×10²²N. If we were to simply substitute Earth in place of Ganymede at the same orbital distance the gravitational attraction would be 6.60066078×10²³N. An Earth-mass object would have to orbit much faster (2.4x??) in order to compensate for the greatly increased gravitational attraction.
We know the mass of Ganymede because of its distance from Jupiter and its orbital speed.
So, no, you have to break physics to make this work.
answered 1 hour ago
Ian Moote
66419
add a comment |Â
up vote
1
down vote
up vote
1
down vote
This could not happen.
Knowing what we know of Earth, Ganymede, and Jupiter, the gravitational attraction between Jupiter and Ganymede is 1.637795249×10²²N. If we were to simply substitute Earth in place of Ganymede at the same orbital distance the gravitational attraction would be 6.60066078×10²³N. An Earth-mass object would have to orbit much faster (2.4x??) in order to compensate for the greatly increased gravitational attraction.
We know the mass of Ganymede because of its distance from Jupiter and its orbital speed.
So, no, you have to break physics to make this work.
answered 1 hour ago
Ian Moote
66419
This could not happen.
Knowing what we know of Earth, Ganymede, and Jupiter, the gravitational attraction between Jupiter and Ganymede is 1.637795249×10²²N. If we were to simply substitute Earth in place of Ganymede at the same orbital distance the gravitational attraction would be 6.60066078×10²³N. An Earth-mass object would have to orbit much faster (2.4x??) in order to compensate for the greatly increased gravitational attraction.
We know the mass of Ganymede because of its distance from Jupiter and its orbital speed.
So, no, you have to break physics to make this work.
answered 1 hour ago
Ian Moote
66419
answered 1 hour ago
Ian Moote
66419
answered 1 hour ago
Ian Moote
66419
answered 1 hour ago
Ian Moote
66419
66419
add a comment |Â
add a comment |Â
Admiral Jota is a new contributor. Be nice, and check out our Code of Conduct.
Admiral Jota is a new contributor. Be nice, and check out our Code of Conduct.
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Welcome to Worldbuilding. Please take the tour and visit the help center. Can you add a tag explaining which kind of answer are you looking for? Science based or magic?
– L.Dutch♦
2 hours ago
Thanks. I added the science-based tag, and I'm checking out the tour right now.
– Admiral Jota
2 hours ago
1
Are there aliens or Q involved? Gravity is linked to mass, and both govern orbital characteristics, so unless there is some external force at play, gravity is set for Ganymede. Also, did life evolve there, or was it seeded? Because humans are not inevitable as a product of evolution...
– bukwyrm
1 hour ago
I'm pretty flexible on the ultimate origins of life there. I could happily go with an "ancient aliens seeded both Earth and Ganymede billions of years ago" theory if that makes things easier. And I'd be fine with suggesting those ancient aliens used some unknown advanced technology or "impossible" materials to intentionally craft an ideal environment there.
– Admiral Jota
1 hour ago
Another thought: I don't necessarily need the entire moon to have a high gravity. I only need a high-gravity environment that's large enough for a small underground civilization. Spinning an entire cave system seems rather unrealistic, but perhaps there are other good pseudo-gravity options? Or could I have a single highly dense point that produced high G's in a small area that dropped off substantially with distance?
– Admiral Jota
1 hour ago