World building idea: Jupiter-sized Earth

doctorbadwolf

Heretic of The Seventh Circle
Ha, no need. But I think the fact that you are a physicist puts you in a different category of reader than most. Most don't care or won't notice the things that you notice. Meaning, it is more difficult to suspend your disbelief than mine, at least as as the science goes. In other words, you've got the problem of expertise, which isn't unlike being an audiophile: it is nice to have a developed ear, but the problem is that an audiophile can enjoy music less often than someone who doesn't have an ear for quality hifi.

On the other hand, while you lose enjoyment in one place--e.g. a SF movie with dubious science--you might gain it in other words, e.g. a SF movie with good science that you get to enjoy the subtleties of that others miss.

(As a side note, about a year ago I purchased a really nice Marantz amplifier with Elac speakers...it is wonderful to hear music with such great sound, but it has reduced my tolerance for sub-par bluetooth speakers and such, so in a way it has made me enjoy music less, unless I'm in the room with my stereo, and most of my music listening is in the kitchen, which is where that stereo isn't!)
I am vehemently opposed to narratives that are basically “ADHD is really a superpower!” or whatever, but the forgetfulness that comes with my ADHD is a blessing in a couple ways, this effect being one of them. I essentially don’t ever experience what you describe except with food, and even then it is very muted.

And thank goodness because I love hifi music but also have no patience for like…ever not having music on around me. It would suck butt to not be able to enjoy music on my phone…
 

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Lanefan

Victoria Rules
This is actually an idea I'm playing with for a writing project, but thought the smart folks of ENWorld could offer good advice.

The basic idea--at least relevant to discussion here--is a Jupiter-sized world, but one that is inhabitable by humans.

Some questions:

*What are some basic factors I'd need to consider? Stuff like seasons, weather, climate, yearly and daily cycles, etc.
Weather and climate would be the biggest headaches; and tides if the sun and-or any large moons are close enough.

My first major world was a bigger-than-Earth affair and I soon came to realize that the weather would end up balls-nuts crazy a lot of the time compared to what we're used to, simply due to scale and the sheer size of the different climatic zones. The hot areas, being bigger, would get hotter; the cold areas colder, and the temperate-zone interactions between the two would thus tend to be more violent.

Tides are another issue: you'd probably have a much bigger difference between high and low tide levels in many places, again due to scale.

The other thing to consider is astronomy. A bigger world is going to be a heavier world (unless it's hollow), meaning it's going to be farther from its mother star, by extension meaning a typical sun-like star won't do unless you want your world to be too cold for Human inhabitation. So, you'll need a different star type...and once you've determined that, you're right back to weather again because incoming heat from the sun is what ultimately drives almost all day-to-day weather on the planet (volcanic activity and forest fires cause the rest, a trivial but not-zero amount).
 

Umbran

Mod Squad
Staff member
Supporter
Tides are another issue: you'd probably have a much bigger difference between high and low tide levels in many places, again due to scale.

Um, when we get to tides for this large, but not dense, world, things will get complicated.

On Earth, we see tides in the ocean, but the tidal forces affect the entire planet. For Earth and its moon, we don't notice the effect on the rock of the planet on a day to day basis, because there's a whole lot of strong rock. The ground only flexes a bit (about one foot, actually), while the water, being fluid, moves a lot more.

But, this low-density, large planet, is a different beast. If we are talking about a thin shell - that one foot of movement is a large flex for a 30-foot thick shell like the dyson sphere discussed above.

The other thing to consider is astronomy. A bigger world is going to be a heavier world (unless it's hollow), meaning it's going to be farther from its mother star

This is incorrect. In our own solar system, the heavy worlds are farther from the sun, but that's not a general rule, by a long shot.

1634309913855.png

In general, on this scale, for the most part we can use radius as a proxy for mass - it is hard to be 10 times bigger and not be heavier - and we won't be too far off.

The Earth is down at the lower left area of the graph (one earth radius, and 93 million miles from the sun). You'll note that Jupiter-sized worlds (along the top of the plot) exist all along the spectrum from around 1 million to a hundred million miles from their parent star.

There is a scarcity of middling sized worlds near their stars (in the "Neptune Desert" region. But big and small worlds are found all over the place.
 
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Someone mentioned pumice as a less dense rocky material. I think it'd make for a great way to get around rocky planet gravity at the scale you're talking about and create an interesting game world.

Instead of being solid, it's more of a hive or foam like structure, with massive empty spaces traversed by a lattice of stone. This would lead to a lot more verticality in the environment that could lead to some really cool features.

Underground oceans
Gliders, zip lines and cable cars as significant means of transportation
Roads that are literal highways.
 

One other somewhat general point about gravity at from a "how would people live there?" perspective though. From an anatomical perspective, you don't really have to make any kind of special allowances.

Physics for D&D is really only based on a small subset of gamist abstractions that tell you what your character can do. These abstractions exist independent of the physical characteristics of the setting. Basically characters can do what the book says they can do.

You can of course narrate special reasons for their ability to survive, but "they grew up that way" is also a perfectly adequate response. It only really matters if your PCs venture into an area with different physical characteristics.
 

Tonguez

A suffusion of yellow
Someone mentioned pumice as a less dense rocky material. I think it'd make for a great way to get around rocky planet gravity at the scale you're talking about and create an interesting game world.

Instead of being solid, it's more of a hive or foam like structure, with massive empty spaces traversed by a lattice of stone. This would lead to a lot more verticality in the environment that could lead to some really cool features.

Underground oceans
Gliders, zip lines and cable cars as significant means of transportation
Roads that are literal highways.
it would certainly be an interesting environment
but I am wondering about its formation - Pumice is formed from the explosive eruption of magma, so for a planet sized pumice you would need to have a magma core with explosive, gassy breakthroughs that then cool into a compact planet

hmmm I suppose the left over remnant of a giant planet that exploded might be feasible - but for the remnant to be jupiter-sized means the original rocky planet was of mindblowing proportions
 

it would certainly be an interesting environment
but I am wondering about its formation - Pumice is formed from the explosive eruption of magma, so for a planet sized pumice you would need to have a magma core with explosive, gassy breakthroughs that then cool into a compact planet

hmmm I suppose the left over remnant of a giant planet that exploded might be feasible - but for the remnant to be jupiter-sized means the original rocky planet was of mindblowing proportions
Maybe something like a sponge or a coral, some fantasy creature is ingesting fantasy space debris and excreting land. Maybe it was generated as a chemical byproduct of a reaction between bubbles of fantasy space gasses? Perhaps it once was solid and something (like an explosion) happened.

Each of these could have different implications and they're all fun (imho)
 



J.Quondam

CR 1/8
Maybe something like a sponge or a coral, some fantasy creature is ingesting fantasy space debris and excreting land. Maybe it was generated as a chemical byproduct of a reaction between bubbles of fantasy space gasses? Perhaps it once was solid and something (like an explosion) happened.

Each of these could have different implications and they're all fun (imho)
Or perhaps something is eating th planet way from the inside, and excreting the waste... somewhere else? Some other plane, maybe?

One of my settings is the interior surface of a massive 100 mile-diameter cavern on/in the Plane of Earth. It was carved out by elemental motes embedded within it, that eroded the earth away, leaving behind the immense cavity, including some adamantium "pillars" that crisscross the void here and there.
 

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