# QuestionJupitearth

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#### vincenzosassone

Do you think OP will like it?
I only hope she will see the post, I'm sure she will like it.

Catastrophe

#### Catastrophe

##### The devil is in the detail
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
My suggestion would provide massive increased living space without increasing mass / volume of the planet. It could still be little more massive than Earth. Increasing mass to give a planet e.g., 3 x Earth size would increase temperature and pressure in core with widespread effects, some possibly very unfavourable.

Cat

#### Lariliss

Excuse me in advance for making disturbance.
Having the Earth carrying capacity ~9 bln and less than 30% of solid surface (even let's take 1 number for habitable earth surface), it would be possible to calculate approximate surface square kilometre and thus radius that is needed.
If it is an acceptable calculation method, than making models of the planet matter might be more comprehensive.

Catastrophe

#### Catastrophe

##### The devil is in the detail
Lariliss, OP stated no oceans, hence 100% land surface. Tops of my suggested model can be for hydroponics or even soil for growing food and / or shielding radiation / micrometeorites. If radiation not deleterious to foodstuffs.

Depending on the geology, which is under control of the author, (as is radiation) the planet surface might provide raw material for building upwards. Thus living space can be created without changing planetary mass. For example, bricks (possibly large baked sheets) might be reinforced with available metal frame. It all depends on what OP decides.

Radius is only increased by height of buildings. Correspondingly mass. The idea is just an extension of having a city of skyscrapers. "Streets" between "buildings" could have reflectors to channel sunlight sideways into "internal fields" for food production.

Cat

#### Lariliss

Lariliss, OP stated no oceans, hence 100% land surface. Tops of my suggested model can be for hydroponics or even soil for growing food and / or shielding radiation / micrometeorites. If radiation not deleterious to foodstuffs.

Depending on the geology, which is under control of the author, (as is radiation) the planet surface might provide raw material for building upwards. Thus living space can be created without changing planetary mass. For example, bricks (possibly large baked sheets) might be reinforced with available metal frame. It all depends on what OP decides.

Radius is only increased by height of buildings. Correspondingly mass. The idea is just an extension of having a city of skyscrapers. "Streets" between "buildings" could have reflectors to channel sunlight sideways into "internal fields" for food production.

Cat
Dear Cat,
At some point of the discussion I've got (and internally agreed ) this idea of skyscrapers.
But I am not sure anymore if it is accepted.
Having surface parameters and hence the radius, we may give different scenarios for geology that will work (or will be possible to work).
At some point I even thought of a brain-like surface. But it should be with minimum mountains and minimum of water.
I mean, it wouldn't be necessarily gas giant trying to instill life.

No argue, I must have lost the key idea (but I have read very carefully and double-checked).

Catastrophe

#### Catastrophe

##### The devil is in the detail
I never thought for a second that anyone was suggesting a gas giant. That is just so impossible.

I was trying to make the point that you don't need a 3 x Earth size - the complications are ginormous and the 'advantages' are negative. Just check pressure and temperature as radius increases. Look at the effects on tectonics, volcanism - affect on land surface usability.

I know the original idea was to be scientifically compatible, but that there was some scope for change. If OP ever returns, it would be interesting to see the reactions to the way this has been drifting.

Cat