The Worldbuilding Questions Thread
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? dhok posts: 235
, Alkali Metal, Norman, United States
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How large can I make my main world, but retain an Earth-like magnetic field and Earth-ish (not necessarily exact, but mostly so) gravity?
? Torco Learner of Stuff
posts: 220
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I once did some maths and some research and came out with something like three earth radii, if you push the density and rotation speed as low as you can. I can't remember how i came to that particular number, so don't believe me.
Of course, there are other considerations that worry me about three-earth-radii worlds: for example, wouldn't such a large world be a lot more stratified than our own, thus having a much lower concentration of iron and other heavy stuff on the surface? not enough of a low concentration for it to have biological effects, like no one's getting anemia unless they don't eat properly, but we're still considering civilization-spanning differences when we start considering mining and whatnot. I mean does a world without metal technology look like? We've got *some* inkling of that amongst island peoples, like The Conworlder 1 played with the idea briefly but got distracted from by an episode of Doctor Who.

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1. Yes. This is my religion faith: On a realm infinitely more real than our own a great orange-and-jade goddess has wished us all into existence during her free time, and when we die we go to an even less real realm called The Kitchen Sink, which is what Heidegger had a wisp of an intuition of when he wrote of Das Nichts: this is where all that is forgotten is laid to rest. Also I are high
? dhok posts: 235
, Alkali Metal, Norman, United States
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Three earth radii is a bit much even for my planet- I was thinking more like a radius and a half. This planet also has two moons; I don't know whether they're Moon-sized, though. I am thinking that they would be in some sort of orbital resonance with each other, and be used in early date-keeping. (For example, let's suppose the inner moon has a period of 15 days, and the outer moon one of 25 days, in a 3:5 resonance. Then several cultures would have a seventy-five day "month" based on the transit of the moons.)

A planet with a radius three times that of Earth is an interesting idea, because, I think, wide-ranging planetary colonization would have to wait for the steamship. But I'm not sure whether I want to do that.
? Nessari ?????? ?????? ????????
posts: 932
, Illúbequía, Seattle, Cascadia
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FYI, double moons are a nightmare to work out.
? Hâlian the Protogen
posts: 141
, Alípteza, Florida
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And of course Daia has two moons.

I know one has an orbital period of 22 days, and the other 40 days, therefore an 11:20 resonance and whence the 440-day year, but that's about it.
? Hallow XIII Primordial Crab
posts: 539
, 侯 at Basel, Switzerland
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multiple moons essentially means you are best off handwaving most of the orbital parameters unless you are v. good at maths or know somebody who is

also dhok congratulations on the comma in the thread title
? dhok posts: 235
, Alkali Metal, Norman, United States
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quoting Nessari, Illúbequía, Seattle, Cascadia:
FYI, double moons are a nightmare to work out.

What makes them such a nightmare? Is it just their gravitational interaction with each other? If I have a preset orbital resonance in mind, can I figure out what size and distance I need for the moons?
? Morrígan Witch Queen of New York
posts: 303
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Yes, also because it becomes (minimally) a 3-body system (4 if you count the star),  and a 3-body system is the largest for which an analytical solution is possible; it is, however, still very difficult and involves (I think) an infinite power series.

Unless you can treat the mass of one object as negligible, in which case it becomes more manageable.

Three-Body Problem
? dhok posts: 235
, Alkali Metal, Norman, United States
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Hmm. What if the planet has a ring system, and the inner moon is a ring shepherd with very little mass?

(Not a large ring system. Just a couple of thin bands of rock.)
? Morrígan Witch Queen of New York
posts: 303
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It's doable, I mean it's not like these system are hugely unstable. Might have to check it out in Universe Sandbox, which I do not own but might feel the need to buy.
? Nessari ?????? ?????? ????????
posts: 932
, Illúbequía, Seattle, Cascadia
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quoting dhok, Deacon, Norman, United States:
Hmm. What if the planet has a ring system, and the inner moon is a ring shepherd with very little mass?

(Not a large ring system. Just a couple of thin bands of rock.)

You're not really cutting down the math necessary. Like Morrígan said, it's doable, just takes a fuckton of work unless you're willing to just handwave.
? dhok posts: 235
, Alkali Metal, Norman, United States
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Hmm, maybe I do want to buy Universe Sandbox...
? Nessari ?????? ?????? ????????
posts: 932
, Illúbequía, Seattle, Cascadia
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…WHY DID NO ONE TELL ME THIS WAS A THING
? Nessari ?????? ?????? ????????
posts: 932
, Illúbequía, Seattle, Cascadia
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quoting Morrígan, Countess:
It's doable, I mean it's not like these system are hugely unstable. Might have to check it out in Universe Sandbox, which I do not own but might feel the need to buy.

quoting dhok, Deacon, Norman, United States:
Hmm, maybe I do want to buy Universe Sandbox...

Yes you do you do you so very much do oh my gods this is amazing

And I am spending entirely too much time recreating Ceres x4 colliding in a "cubic symmetry" orbit.

I have a shit1 graphics card and it's this amazing you people with better stuff need to look at this on your own systems.

edit: ok last addition:
Create > Collision > More Collisions > (Sun & (Jupiter x30) x3)

is a preset in this.

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1. where shit means just barely within the suggested specs for this.
? Torco Learner of Stuff
posts: 220
, Conversational Speaker message
i bought it on a sale on steam a while ago... never got around to downloading it.
? Torco Learner of Stuff
posts: 220
, Conversational Speaker message
i bought it on a sale on steam a while ago... never got around to downloading it.
? Morrígan Witch Queen of New York
posts: 303
, Marquise message
You might want to do it again, i think there is a much better "2" version, with better math. According to Scott Manley.
? Nessari ?????? ?????? ????????
posts: 932
, Illúbequía, Seattle, Cascadia
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Yes yes yes
also it's technically Universe Sandbox ². This is the one up on the Universe Sandbox age.
? Torco Learner of Stuff
posts: 220
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ain't nobody got cash fo tha'
? Rhetorica Your Writing System Sucks
posts: 1292
, Kelatetía of Space
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...I bought it.
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