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  1. - Top - End - #1
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    BarbarianGuy

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    Default How ridiculous is my planet?

    I'm working on a game setting (for D&D, but it shouldn't matter for this discussion), and I have my world designed for narrative purposes. I'm curious if what I've built is feasible, although I am invoking magic/Clarketech for some of it. Still, can't hurt to run it by some geology- and physics-minded folk.

    Okay, here goes.

    The planet is about the size of Earth's moon. It's based on a manufactured spherical construct, and still has 1G at the surface. I read somewhere that if you could build a planet out of osmium, you could get 1G at the surface with a radius half that of Mercury, so I don't think it's physically impossible to have it with something Moon-sized. But again, I'm happy to say a deity did it with this (e.g. enhanced artificial gravity). We'll say it has an Earth-like tilt and orbits a smaller, redder star than the Sun, but close enough to be in its goldilocks zone. Is orbital speed purely a function of mass and distance? I'm guessing this means a year would be shorter than ours. It had a small moon of its own (proportionately maybe the same as our own is to Earth) but it broke up and is in the process of forming a ring. That happened recently enough that there's still a cluster of mass, creating a lopsided ring, if that's at all possible.

    I want it to have an Earthlike atmospheric density at the surface, and it probably needs a magnetic field to keep that intact. Given the size and gravity, how does that change the density gradient? How high up would you need to get to have top-of-Everest conditions in terms of thinness and temperature?

    The original construct is a single, smooth sphere that houses colossal alien machinery and whatnot. Over the eons, the surface has collected water and dirt and stuff from passing asteroids and comets (a process which may have been "helped" by its Sufficiently Advanced Creators, if necessary to get the amounts I need). This stuff built up to a layer ranging from maybe two miles thick to as much as twenty. It eventually gets shaped and cleaned up by powerful entities into land and oceans. The landmass is a single belt that runs around the equator, about 500 miles wide (250 miles north and south of the equator, total area about the same as the 48 contiguous US states). I have this idea that there are passages deep underneath that allow the oceans to balance each other. The poles are just ice caps, like the Arctic. The north and south oceans average maybe a couple of miles deep, but might have really deep spots here and there.

    This structure means no volcanoes or earthquakes, except maybe very tiny quakes as things periodically settle. There's also a dearth of ore, so refined iron/steel would be pretty hard to come by. Geology as a science would be weird, and unlike what we have here on Earth. I'm not sure geological layers would exist in any meaningful sense.

    Along the center of the continental belt is a single mountain range that runs all the way around the world. I'd like the height of this to be roughly like Everest in terms of atmospheric density, but I'm not sure how high that would be. I assume the mountains would also interfere with winds and rainfall and such, but given the generally symmetrical layout of the continent, I'm not sure how that would work. Would both sides of the range see lots of rainfall? Would it vary by season? Speaking of seasons, the equatorial land arrangement seems like it would also mean there's little difference between spring and fall.

    The entities that shaped the landmass also seeded it with life, so if water flows "outward" (north and south) from the central ridge, there would be forests or at least some plains and whatnot. I don't know if there would be any sizable deserts anywhere, unless my configuration prevents much rainfall at all.

    So that's mostly it. The tl;dr of it is, how high should those central mountains be if I want them to feel like going up to the Himalayas, and how does precipitation work? And I guess, are there any gotchas I didn't think of?

    Thanks!

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    Default Re: How ridiculous is my planet?

    I'll try to provide what I do know, but please note I'm on at least one slope of Mt. Stupid on all these subjects. I'll guess the rising one, based on the evidence.

    Rainfall:
    If the highest elevation is a ring around the equator then rivers flow poleward, no ifs about it. The more relevant figure to the environment is the amount of rainfall.

    For rainfall, we're looking at the planet's Hadley cells. Earth has six such cells (three per hemisphere) and my understanding is that there's an odd number per hemisphere at all times. I found a rundown summarizing the possibility of earth having only one cell per hemisphere in the past here, and the relevant information is that in either case (1 or 3 cells per hemisphere) winds at the surface should run toward the equator from both sides of your landmass. So there's only likely to be a desert in the rain shadow of any other mountain ranges.

    Summer in the hemisphere will probably create a rainy season on that side of the central mountain range, as higher temperatures allow more water to be carried equatorward. So there'd be a lack of Chaparral even compared to modern earth, to the point I doubt any would exist. Otherwise, all the land being equatorial probably prevents significant seasonal variation (you're pointed more or less directly at the sun all year).

    Magnetism:
    Our magnetic field is a result of the motion of earth's outer core. I think you're planet would would have a proportionally larger core (more heavy metals is an easy explanation for the higher density).

    Maybe the densest material in your planet makes up the inner core, and most of your outer core is still (magnetic) iron? I'm not sure what impact that would have on the strength on the magnetosphere, though.

    Elevation:
    The only thing I think I can say about elevation is that without active tectonics your mountain range is going to be shrinking every year. Sorry; not an area I've read up on.

    The Ring:
    What I do know about planetary rings is that they form when material that could coalesce into a moon is kept apart by tidal forces, and therefor exists closer to the planet than the moons are. If the moon is in the process of getting too close, it would probably start to break up, starting with a lopsided ring. You're just in that early phase before an evenly spread ring and well before the ring is eventually destroyed.

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    Barbarian in the Playground
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    Default Re: How ridiculous is my planet?

    Quote Originally Posted by EggKookoo View Post
    Is orbital speed purely a function of mass and distance?
    Not even that. Kepler says t = 2*pi*sqrt(a^3*mu), where mu is gravitational constant and a is semi-major axis. So, the only thing that determines how long an orbital period is is how far apart the two objects are.

    Quote Originally Posted by EggKookoo View Post
    I'm guessing this means a year would be shorter than ours.
    Yup. And remember that seasons are a function of axial tilt, so if you want winters you will either have to use that or make the orbit unusually eccentric.

    Quote Originally Posted by EggKookoo View Post
    It had a small moon of its own (proportionately maybe the same as our own is to Earth) but it broke up and is in the process of forming a ring. That happened recently enough that there's still a cluster of mass, creating a lopsided ring, if that's at all possible.
    Possible sure, but realistically, the density of it will be far less than you expect. Look at some videos showing how little material per volume actually is inside of Saturn's rings or asteroid belts for an idea.

    Quote Originally Posted by EggKookoo View Post
    I want it to have an Earthlike atmospheric density at the surface, and it probably needs a magnetic field to keep that intact. Given the size and gravity, how does that change the density gradient? How high up would you need to get to have top-of-Everest conditions in terms of thinness and temperature?
    No idea about temperature, but atmospheric density is mostly dictated by gravity and rotational speed - you need some amount of gravity to keep a given amount of gasses from escaping the atmosphere if they get heated up. You have 1G at your disposal, so you can have Earth-like atmosphere, provided the rotational speed isn't wildly different.

    Quote Originally Posted by EggKookoo View Post
    The original construct is a single, smooth sphere that houses colossal alien machinery and whatnot. Over the eons, the surface has collected water and dirt and stuff from passing asteroids and comets (a process which may have been "helped" by its Sufficiently Advanced Creators, if necessary to get the amounts I need). This stuff built up to a layer ranging from maybe two miles thick to as much as twenty. It eventually gets shaped and cleaned up by powerful entities into land and oceans.
    30-70 km is about the thickness of Earth's crust, so you get no problems there. The temperature that deep would actually be lower than that of Earth, since much of ours comes from decay of radioactive elements in the mantle - or much higher, if that alien machinery produces heat.

    Quote Originally Posted by EggKookoo View Post
    This structure means no volcanoes or earthquakes, except maybe very tiny quakes as things periodically settle. There's also a dearth of ore, so refined iron/steel would be pretty hard to come by. Geology as a science would be weird, and unlike what we have here on Earth. I'm not sure geological layers would exist in any meaningful sense.

    Along the center of the continental belt is a single mountain range that runs all the way around the world. I'd like the height of this to be roughly like Everest in terms of atmospheric density, but I'm not sure how high that would be.
    You will run into problems with erosion eventually. There is no process to create new mountains, os the old ones would just... slough down over time. That puts a bit of a limit on how old your planet can be if it still has mountains that tall. Also keep in mind that on a smaller size of a planet, a mountain of a given size will experience more forces from the rotation that will try to tear it apart.

    Quote Originally Posted by EggKookoo View Post
    I assume the mountains would also interfere with winds and rainfall and such, but given the generally symmetrical layout of the continent, I'm not sure how that would work. Would both sides of the range see lots of rainfall? Would it vary by season? Speaking of seasons, the equatorial land arrangement seems like it would also mean there's little difference between spring and fall.
    Seasons come from axial tilt, as for weather, large scale winds are pretty stable - look up global wind patterns. You will see more regional extremes, though, since you have no Gulf stream equivalent.

    Quote Originally Posted by EggKookoo View Post
    The entities that shaped the landmass also seeded it with life, so if water flows "outward" (north and south) from the central ridge, there would be forests or at least some plains and whatnot. I don't know if there would be any sizable deserts anywhere, unless my configuration prevents much rainfall at all
    You would still have potential for some in places where those wind patterns fork off right as they hit the coastline. There is one such area on the east coast of south america, IIRC.
    That which does not kill you made a tactical error.

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    Default Re: How ridiculous is my planet?

    If your land mass is only 500 miles wide but you have high mountains down the middle I expect there would not be much land left on either side.
    Quote Originally Posted by Flickerdart View Post
    Why be Evil when you can be Lawful?

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    Default Re: How ridiculous is my planet?

    Okay, so better than I feared. It sounds like my biggest hangup is going to be explaining the existence (and persistence!) of the mountain range. And then also why my landmass north and south of it hasn't just washed into the oceans by now.

    Assuming I come up with some justification for that, it seems like the summer for each hemisphere will be the rainy season and the winter will be the dry season. And while it's not certain, it seems like atmospheric density probably drops off at about the same rate as it would on Earth, so "Everest conditions" would exist at about the same height above sea level (give or take).

    The moon that broke up would be much smaller or at least less dense than ours, proportionately. I can live with that, it's more about the (partial) ring now anyway.

    Reading about goldilocks zones and small red stars, it looks like K types are safer than M types (M are the smallest, but longest-living at ~100 billion years). An M star's small size means its goldilocks zone is in very close, and at that distance the planet is awash in hundreds of times as much radiation as we are here at our distance. What I'm reading describes it as an obstacle for life evolving, but I'm not sure how hard it would make it for complex life that arrives on the planet to continue to survive. Maybe with a higher amount of mutation, but that's actually a theme of my setting anyway so I could roll with that. And the artificial construct could generate a strong magnetosphere to protect the machinery. Would make for some really nice auroras. Or I could just put it around a K star and deal with less radiation (~45 billion year lifespan is plenty of time), but I like the extreme feel of the M.

    Regarding year length, it's hard to come up with anything precise. The assumption in real life is that any planet in an M star's habitable zone is likely going to be tidal-locked, which alters the distance/temperature equation. I don't want that, so I kind of have to wing it. I'm going to say a year is around 120 (Earth) days, and arbitrarily set a day to be 24 hours so I can make the setting feel normal. I can work out some calendars based on that.

    Thanks, this has been very helpful.

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    Default Re: How ridiculous is my planet?

    Originally Posted by EggKookoo
    …at that distance the planet is awash in hundreds of times as much radiation as we are here….

    Maybe with a higher amount of mutation….
    Keep in mind that elevated radiation levels will, on balance, cause much more harm in terms of tissue destruction than they will “help” with rates of speciation. Overall a hard-radiation environment will greatly reduce species diversity, so a close-in orbit to an M-dwarf will create intense problems for terrestrial ecosystems, especially around a flare star like the binary UV Ceti.

    Marine biodiversity would be less affected, and deep-sea rift vent ecosystems would be viable, or even shallower-water ecosystems in an epicontinental sea, if you have an energy source closer to the surface. But for complex terrestrial ecosystems on a planet close to an M-dwarf, you will need one hella magnetic field.

    —Or, since your planet will almost certainly be tidally locked anyway, lean into that and work with the possibilities for terminator/nightside ecosystems. Radiation will still be an issue, but if you have the bulk of the planet between you and the star there’s at least some protection.

    Originally Posted by EggKookoo
    Regarding year length, it's hard to come up with anything precise.
    If you haven’t already, you might look into the TRAPPIST-1 system, which is a beautiful cosmic phenomenon in its own right, and very helpful to get a feel for these tightly bound red dwarf planets. If you want an extreme feel, TRAPPIST-1 is a good place to start.

    Originally Posted by EggKookoo
    Over the eons, the surface has collected water and dirt and stuff from passing asteroids and comets (a process which may have been "helped" by its Sufficiently Advanced Creators, if necessary to get the amounts I need).
    You probably won’t need much help with that. Planets orbiting close to stars tend to bear the brunt of all the debris drawn inward by the stars’ gravity, which is why Mercury has such a high density of craters. Assuming nothing too massive cracks your planet apart, you should have a substantial buildup of material. A few close passes by other stars (possibly halo stars plunging through the galactic disc) to disrupt the Oort cloud should bring you all the water you need.

    Originally Posted by EggKookoo
    The landmass is a single belt that runs around the equator, about 500 miles wide….

    Along the center of the continental belt is a single mountain range that runs all the way around the world. I'd like the height of this to be roughly like Everest in terms of atmospheric density, but I'm not sure how high that would be. I assume the mountains would also interfere with winds and rainfall and such….
    So, it sounds like you have a waterworld with moderately deep oceans and a very thin ribbon of land wrapping around the equator.

    Ocean circulation will be in terms of bands rather than gyres, and you’ll have few to no hurricanes, although this depends how close you are to the parent star. A tidally locked ocean world in the habitable zone of an M-class dwarf will have severe weather patterns, likely more severe than will be convenient for you. Going with a K-class star will remove this issue, along with the radiation and other issues, so I’d advise that for general headache relief.

    Originally Posted by EggKookoo
    Would both sides of the range see lots of rainfall?
    Most likely yes, since your landmass is on the equator, and the local version of trade winds will be bringing constant moisture all along the slopes of the equatorial mountains.

    On Earth, the Intertropical Convergence Zone (ITCZ) wanders back and forth owing to seasons and other factors, but averages out to be a few degrees north of the physical equator, since Earth happens to have more landmass in the northern hemisphere right now. On your planet, the ITCZ would probably wobble more tightly right around the equator, since there are no landmasses north or south of the equator to influence its position.

    As a first approximation, I would expect your equatorial land belt to be very much like Hawaii, with orographic rainfall on both northern and southern slopes. There would probably be a rainier season and a less-rainier season for the northern and southern flanks, but heavy rains overall would be the norm. This would cause a lot of erosion, so you would quickly run into issues of soil loss.

    Originally Posted by EggKookoo
    It sounds like my biggest hangup is going to be explaining the existence (and persistence!) of the mountain range. And then also why my landmass north and south of it hasn't just washed into the oceans by now.
    Exactly so. Without plate tectonics to drive new mountain-building, and especially given the constant weathering from tropical rains, your equatorial mountains will be worn down very quickly in geological time.

    .
    Last edited by Palanan; 2021-06-21 at 08:16 AM.

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    Default Re: How ridiculous is my planet?

    I don't want the planet to be tidal-locked. I can imagine its creators spun it up, but considering the radiation issue I should probably just move it to a K star. I'll have to live with only 45 billion years of stellar life.

    Regarding the mountains and erosion, I'll probably have to build in some kind of landmass-building process. Given that the "gods" of this place built up the equatorial continent in the first place, it's easy to imagine they set some process in motion that migrated material across the surface toward the equator, where it built up. Maybe after an initial rapid-accumulation period, they set it into some kind of maintenance mode. They're all dormant/sleeping now, and it's been running on automatic for, say, a million years. Enough to keep stuff in place. It's a little heavy-handed but perhaps it can't be helped.

    Awesome feedback!

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    Default Re: How ridiculous is my planet?

    The planet is about the size of Earth's moon. It's based on a manufactured spherical construct, and still has 1G at the surface. I read somewhere that if you could build a planet out of osmium, you could get 1G at the surface with a radius half that of Mercury, so I don't think it's physically impossible to have it with something Moon-sized. But again, I'm happy to say a deity did it with this (e.g. enhanced artificial gravity).
    giving the planet a spin will help (the scientist who's work you read probably assumed such). Don't know this osmium crap but given that it is a construct you can have about any material in the core even if it makes it partially hollow.

    Typically size is not the issue; it is density per amount of volume.

    We'll say it has an Earth-like tilt and orbits a smaller, redder star than the Sun, but close enough to be in its goldilocks zone. Is orbital speed purely a function of mass and distance?
    kinda...

    Without knowing the 'power' behind the sun and with mini planet having the same mass as earth you might be asking a moped to pull the same load as a harley. A star is still a star so your planet will orbit; day, year and season lengths might be a lot different. Season also relies on planet tilt...

    Not a deal breaker in any case; if you have a scientist in your group try to not put his character in a spacecraft able to take a peek.


    I want it to have an Earthlike atmospheric density at the surface, and it probably needs a magnetic field to keep that intact. Given the size and gravity, how does that change the density gradient? How high up would you need to get to have top-of-Everest conditions in terms of thinness and temperature?
    not entirely sure about the gradient. Though there is a slight problem (technically the whole thing but it's not a natural planet) as in keeping the gravity the same you have kept the gravity well the same. I am unsure if that is the same as the magnetic field but i do know they are married; weaken one you weaken the other.

    Top-of-everest conditions? The same... plus the difference in size. While our atmosphere is quite thin this planet can be quite thick. So if the gods that built this place weren't thinking and filled it you now have a mini gas giant. No life as we know it can exist on the surface; atmo is just too thick.

    If they did think this far ahead then it (relatively speaking) doesn't matter one bit; Earth-like


    (a process which may have been "helped" by its Sufficiently Advanced Creators, if necessary to get the amounts I need)
    definitely.


    Along the center of the continental belt is a single mountain range that runs all the way around the world.
    and here we come to the first impossibilities; because of how the planet was form. It is tectonicly inactive. There are no natural mountains. Due to impact craters there will be differences in elevation but they will be smoothed down due to erosion.

    I assume the mountains would also interfere with winds and rainfall and such, but given the generally symmetrical layout of the continent, I'm not sure how that would work.
    depends...

    Our trade winds go from east to west and then west to east. It sounds like the (impossible) mountains simple divide north and south. It would not impact weather in the usual sense. Without some way for water passing through the top might be "desert world" and the bottom "normal Europe pardogy here". With winter wonderland at the poles.

    So without a means of sharing water your planet must have at least three biomes unless both sides received equal amounts of water.


    I am not going to touch the moon today...

    The planet, as written, is plausible. It is a high maintenance world where once the gods/precursors leave everyone else is in big trouble if they can't do the work.

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    Default Re: How ridiculous is my planet?

    Quote Originally Posted by EggKookoo View Post
    Okay, so better than I feared. It sounds like my biggest hangup is going to be explaining the existence (and persistence!) of the mountain range. And then also why my landmass north and south of it hasn't just washed into the oceans by now.
    Purple Worm

    that i recommend recoloring into mountain color


    They spend their youth and procreation phase away from the equator eating dirt (sand mostly). As they get older they start getting colder and move closer and closer to the equator. Finally they die sunbathing and become part of the mountain.

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    Quote Originally Posted by Alcore View Post
    Purple Worm

    that i recommend recoloring into mountain color


    They spend their youth and procreation phase away from the equator eating dirt (sand mostly). As they get older they start getting colder and move closer and closer to the equator. Finally they die sunbathing and become part of the mountain.
    I suspect you mean this at least partly tongue-in-cheek, but I actually may go with something like that. But probably something semi-artificial, as I don't want them to migrate too quickly. Ye Olde Mountain Range of Continual Avalanche is less fun than it sounds.

    The creator gods were these massive kaiju things, but maybe even on a larger scale. The mountain ridge might be atop where they're hibernating, and maybe they set subterranean helper creatures/devices that slowly dredge material toward them to help keep them buried and maybe transfer materials and nutrients. I like the classic myth idea that earthquakes are occasional titan movement...

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    Default Re: How ridiculous is my planet?

    Originally Posted by EggKookoo
    I don't want the planet to be tidal-locked. I can imagine its creators spun it up, but considering the radiation issue I should probably just move it to a K star.
    Good choice, that removes all sorts of issues.

    Also, one further thought about oceans and continents. Unless there’s any gap in the equatorial ribbon, you have a continuous landmass circling the planet, which divides the northern and southern hemispheres into two separate oceans which never mix.

    In effect, you’re getting two waterworlds for the price of one, and this opens up the prospects for two entirely separate biogenetic events, meaning two different biospheres—or at least biohemispheres, potentially with fundamentally different and even incompatible metabolic pathways. This opens the prospect for two or more vastly different intelligent species, each evolving in its own isolated marine hemisphere, with your equatorial ribbon of mountains as a barrier and later a contact zone, if the various intelligent species develop ways to leave the ocean and explore the terrestrial habitat.

    You can imagine there would be some interesting cosmologies that might develop, involving what to us would seem like half a planet—a hemispheric ocean blocked by an inhospitable ring of land—which the inhabitants of each marine hemisphere perhaps considering their counterparts to be “demons” beyond the realm of the habitable world.

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    Default Re: How ridiculous is my planet?

    Quote Originally Posted by EggKookoo View Post
    I suspect you mean this at least partly tongue-in-cheek, but I actually may go with something like that.
    I was vary serious. They are large enough to make those underground waterways. Give them the ability to survive underwater and most functions the precursors need to do can be outscourced to them. Fantasy and sci fi can be blessings in making things work if utilized well.

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    Default Re: How ridiculous is my planet?

    So one of the surprising things about the earth is that it still has a lot of heat from it's initial formation. The moon (having proportionately less heat to begin with and les surface area) doesn't. That's why Jupiter is hotter than the earth. This and radioactive decay makes up about at seventh of the heat at the surface of the earth. This artificial planet (unless the machine produces heat) will need to get a little more sunlight.

    Quote Originally Posted by EggKookoo View Post
    We'll say it has an Earth-like tilt and orbits a smaller, redder star than the Sun, but close enough to be in its goldilocks zone. Is orbital speed purely a function of mass and distance? I'm guessing this means a year would be shorter than ours.
    Redder means closer to get the same temperature. Smaller sun means proportionately smaller distance (for same illumination, with slightly shorter year).

    Redder also means that everythings looks weird in a way that's annoying to keep track of, so I'd recommend against it. (are the skies blue with that much less blue light, what do oceans look like? Do Azurite clothes look drab?)

    It had a small moon of its own (proportionately maybe the same as our own is to Earth) but it broke up and is in the process of forming a ring. That happened recently enough that there's still a cluster of mass, creating a lopsided ring, if that's at all possible.
    Kinda-sorta.

    If it the pieces are in an orbit where the moon itself would be stable, most pieces would eventually collide and form back into a moon. That might take a while though.

    I want it to have an Earthlike atmospheric density at the surface, and it probably needs a magnetic field to keep that intact. Given the size and gravity, how does that change the density gradient?
    It makes it easier to have a magnetic field. Magnetic fields fall off with radius cubed, so a scaled down earth would have a stronger magnetic field.

    The artificial nature of the planet allows for wildly arbitrary magnetic fields. Building planet with a much, much stronger than natural magnetic field wouldn't be hard.

    How high up would you need to get to have top-of-Everest conditions in terms of thinness and temperature?
    Same as Earth, just gravity matters here, which will be the same until you're far from the surface.

    There's also a dearth of ore, so refined iron/steel would be pretty hard to come by.
    There would actually be too much of many metals. A lot of earth's heaver metals have sunk to it's inner core. Asteroids tend to be made made disproportionately (relative to the earth's surface) out of heavier metals. I'd imagine gold there would be more like tin here: it's got it's uses and you actually have to find it, but it's nothing special.
    Last edited by Quizatzhaderac; 2021-07-14 at 02:52 PM. Reason: typos
    The thing is the Azurites don't use a single color; they use a single hue. The use light blue, dark blue, black, white, glossy blue, off-white with a bluish tint. They sky's the limit, as long as it's blue.

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    Default Re: How ridiculous is my planet?

    Quote Originally Posted by Quizatzhaderac View Post
    Redder also means that everythings looks weird in a way that's annoying to keep track of, so I'd recommend against it. (are the skies blue with that much less blue light, what do oceans look like? Do Azurite clothes look drab?)
    I was going to handwave this, under the assumption that eyes have adapted to different sensitivities within the visible spectrum. So a blue thing is still "blue" all things considered, even if it's not literally the same as we see it here. At the same time, my intention was to describe some lush red sunsets. I want the setting to channel a bit of Dying Earth, so it fits.

    Quote Originally Posted by Quizatzhaderac View Post
    There would actually be too much of many metals. A lot of earth's heaver metals have sunk to it's inner core. Asteroids tend to be made made disproportionately (relative to the earth's surface out of heavier metals. I'd imagine gold there would be more like tin here: it's got it's uses and you actually have to find it, but it's nothing special.
    I was wondering about that, actually. I might have gold pieces made of actual gold!

    I guess a question is, would mining stuff like iron be any easier or harder than on Earth? There might be too many variable to be able to answer that...

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    Default Re: How ridiculous is my planet?

    You couldn't have gold money, for the same reason you can't have tin money, you just couldn't carry around enough to be that valuable.

    Iron ore would be literally more common than dirt. However I'd think enough time would have passed that it's all oxidized and needs smelting. I'm not too sure on how iron oxides affect soil quality, so maybe the terraformers all tucked it away underground if it was a problem.
    Last edited by Quizatzhaderac; 2021-07-14 at 02:53 PM.
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    Default Re: How ridiculous is my planet?

    Your Mountains

    Axial tilt would create a shadow effect which might be severe enough for glacial accumulation/sublimation. The Everest-scale peaks would be above almost all of your precipitation, so atmospheric vapor would be the main contributor to glacial growth.

    Summer would happen when the sun is on that side of the mountains and winter when that side of the mountain is in shadow. The relationship between the angle of the slope and the degree of axial tilt will determine how long a glacier-forming shadow will exist.

    How hot the sun gets will determine how fast the glaciers melt.

    Cold air will flow down from the glaciers and when these dense pockets hit warm open water storms will form. Lake Maricaibo in Columbia is an example of this. Winter along the tropical shores will be cold and wet, with occaisonal heat waves as the frontal boundry moves inland. These storms may generate hurricanes. They will generate waterspouts and tornados.

    A question: how passable is the mountain range? You might have a biological barrier such that camels are found only in the north and horser in the south, or there may be easy passes and the same creatures populate both sides.

    A Proposal
    Your world once had two moons: a small, dense moon and a larger one that was almost a second planet. This caused the fast-spinning primary to solidify as an oblate sphereoid, and robbed the primary of much of its rotational energy. Its orbit eventually increased to the point that it was flung out into its own orbit around a million years ago and the central mountain range is what's left after the oblate sphernid tries to become a sphere. This would mean increased tectonic activity after ages of tidal flexing, so quakes and volcanos would happen. This might also explain the decay of the remnant moon's orbit.
    It also opens up the potential of epic adventures on the sister-world as it returns from its million-year vacation among the outer planets.

  17. - Top - End - #17
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    BarbarianGuy

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    Default Re: How ridiculous is my planet?

    Quote Originally Posted by brian 333 View Post
    A question: how passable is the mountain range? You might have a biological barrier such that camels are found only in the north and horser in the south, or there may be easy passes and the same creatures populate both sides.
    By nature, not very. But at some point in the past some enterprising empire (or alliance of such) built a roadway along the ridge, weaving around the peaks or in between them. Think Great Wall of China but broader, and like the Wall it's not literally a single road and currently in various stages of maintenance. A lot of kingdoms also built passages up the mountainsides (both north and south) to the road, most of which have also fallen prey to the elements. Still, more than a few are being kept up, and at least one major nation has a nice switchback going up all ~20k feet (haven't decided the elevation of the foothills yet). That's like one of the Wonders of the World.

    So in the current era, there's probably been a lot of migration mainly due to people using these passages for trade, but I also do imagine there are distinct northern and southern species of certain types. Like the real world, though, it's pretty patchwork.

    Quote Originally Posted by brian 333 View Post
    A Proposal
    Your world once had two moons: a small, dense moon and a larger one that was almost a second planet. This caused the fast-spinning primary to solidify as an oblate sphereoid, and robbed the primary of much of its rotational energy. Its orbit eventually increased to the point that it was flung out into its own orbit around a million years ago and the central mountain range is what's left after the oblate sphernid tries to become a sphere. This would mean increased tectonic activity after ages of tidal flexing, so quakes and volcanos would happen. This might also explain the decay of the remnant moon's orbit.
    It also opens up the potential of epic adventures on the sister-world as it returns from its million-year vacation among the outer planets.
    This is very cool! I do, however, have an explanation for the existence of the place. Short version: the world is vast divine machine built by the gods to help them come up with a solution to a flaw in creation. It wasn't meant to be a planet. It's just a big sphere floating in the void, crunching away internally. It became a planet because the gods learned that "aliens" (creatures from another plane) were trying to infiltrate it. So the gods built up the surface and arranged it so intelligent life would appear, and that life would be the foot soldiers in the fight to protect the machine. So, people are white blood cells...

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    Default Re: How ridiculous is my planet?

    If you want a book that covers things like distance to horizon, air pressure change per altitude in different gravities, habitable zones, etc, I'd suggest you take a look at World-Building, by Gillett.
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    Default Re: How ridiculous is my planet?

    Quote Originally Posted by EggKookoo View Post
    I'm working on a game setting (for D&D, but it shouldn't matter for this discussion), and I have my world designed for narrative purposes. I'm curious if what I've built is feasible, although I am invoking magic/Clarketech for some of it. Still, can't hurt to run it by some geology- and physics-minded folk.
    I wanted to chime in from the perspective of someone with a degree in astrophysics to clear up confusion some posts might have and echo what other posts point out.

    Quote Originally Posted by EggKookoo View Post
    The planet is about the size of Earth's moon. It's based on a manufactured spherical construct, and still has 1G at the surface. I read somewhere that if you could build a planet out of osmium, you could get 1G at the surface with a radius half that of Mercury, so I don't think it's physically impossible to have it with something Moon-sized.
    With a radius the same as the moon's and a surface gravity of 1G, you'll have a density of ~20 g/cm3, about 4x that of Earth or Mercury, the most dense of the planets. There are certainly metals that can accomplish this, though they tend to be expensive and rare. A deity could certainly accumulate enough tungsten, gold, lead, or other heavy metals to create such a planet; it's physically possible for this planet to exist.

    Quote Originally Posted by EggKookoo View Post
    We'll say it has an Earth-like tilt and orbits a smaller, redder star than the Sun, but close enough to be in its goldilocks zone. Is orbital speed purely a function of mass and distance? I'm guessing this means a year would be shorter than ours.
    Someone mentioned Kepler's laws of motion, indicating that distance is all that's needed to calculate orbital period. That is only true when orbiting an object with the exact mass of our sun; smaller stars have different orbital periods for a given distance. The orbital period, T, for a planet orbiting a star (in seconds) is:
    T = 2⋅pi⋅sqrt(a3/GM)
    where a is the distance to the star in meters, G is the gravitational constant (6.67×10−11 m3⋅kg–1⋅s–2), and M is the mass of the star in kilograms.

    (To find out how many days your planet's year is, multiply T by 86,400, the number of seconds in a day.)

    Quote Originally Posted by EggKookoo View Post
    It had a small moon of its own (proportionately maybe the same as our own is to Earth) but it broke up and is in the process of forming a ring. That happened recently enough that there's still a cluster of mass, creating a lopsided ring, if that's at all possible.
    A moon that begins to wander too close to its planet will begin to break up as it crosses the Roche limit, an orbital radius based on the ratio of the two densities of the planet and the moon. For your dense planet and a rocky moon similar to Earth's, that limit occurs at about 4 thousand kilometers, or about 2.3 times the radius of the planet. If that moon crossed the Roche limit within a few tens of thousands or hundreds of thousands of years ago, I can easily believe having the exact scenario you propose. The most notable aspect of your lopsided ring will be its short orbit; you'll probably have the large moon cluster pass overhead every few hours at that close of an orbit.

    Quote Originally Posted by EggKookoo View Post
    I want it to have an Earthlike atmospheric density at the surface, and it probably needs a magnetic field to keep that intact. Given the size and gravity, how does that change the density gradient? How high up would you need to get to have top-of-Everest conditions in terms of thinness and temperature?
    I am not as well-versed on atmospheric models, but here's what I can pass along. One of the primary ways a planet loses an atmosphere is when higher temperatures cause molecules to achieve escape velocity. Higher temperatures will cause molecules in the atmosphere to gain more energy and thus some of those molecules are more likely to bounce around enough to fly away from the planet never to return. Lighter molecules such as H2 and He are going to gain more velocity at the same temperatures as heavier molecules such as N2, O2, H2O, or CO2, and so they are more likely to have completely escaped the atmosphere over billions of years. This is the situation with Earth's gravity and temperature, and so it would likely be with your planet.

    The reason a magnetic field is necessary to maintain an atmosphere is that cosmic rays have a nasty habit of photo-dissociating heavier molecules into lighter ones, allowing those to then escape the atmosphere. A magnetic field helps deflect those cosmic rays. Magnetic fields created naturally in planetary bodies exist when three main elements exist. Planets with magnetic fields must have:
    1. an electrically conducting interior (e.g. a metallic core),
    2. a fluid core with convection,
    3. and significant planet rotation (a 24-hour day is sufficient).
    Your proposed planet, allowed to evolve naturally over billions of years, would be missing the fluid core with convection. The ratio of surface area-to-volume increases as a planet's radius decreases; smaller planets have greater surface area compared to their volume. But an increase in this ratio means that the planet cools quicker. The reason Earth's Moon has no magnetic field is that it has no liquid core because it has cooled much quicker than Earth.

    I find this an easy enough fix by saying the deities that created the planet in the first place established some mechanism to generate an "artificial" magnetic field. The alternative would be to have some sort of atmospheric generation, turning liquids and solids into atmospheric gasses, though I imagine it could take millions of years or so for there to be noticeable atmospheric loss without a sufficient magnetic field.

    Finally on atmospheres, my instincts say that atmospheric density gradient might mimic Earth's given similar gravity and atmospheric pressure at the surface, but I have no justification for my instincts.

    Quote Originally Posted by EggKookoo View Post
    The original construct is a single, smooth sphere...
    The conclusions you and others draw regarding rock and water accumulation, weather and ocean currents, Hadley cells, geology, seasons, etc. seem reasonable to me.

    Quote Originally Posted by EggKookoo View Post
    I don't want the planet to be tidal-locked. I can imagine its creators spun it up, but considering the radiation issue I should probably just move it to a K star. I'll have to live with only 45 billion years of stellar life.
    I think this is a good choice on your part. It helps to avoid irradiating the surface and the tidal-locking issue.

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    DwarfClericGuy

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    Default Re: How ridiculous is my planet?

    Quote Originally Posted by EggKookoo View Post
    The planet is about the size of Earth's moon. It's based on a manufactured spherical construct, and still has 1G at the surface. I read somewhere that if you could build a planet out of osmium, you could get 1G at the surface with a radius half that of Mercury, so I don't think it's physically impossible to have it with something Moon-sized. But again, I'm happy to say a deity did it with this (e.g. enhanced artificial gravity).
    Luckily gravity is easy to increase: just put something ultra-dense (like a piece of degenerate matter, an artificial black hole, or MACHO-variant dark matter) inside the structure. Some of those have interesting secondary effects, too.

    Quote Originally Posted by EggKookoo View Post
    We'll say it has an Earth-like tilt and orbits a smaller, redder star than the Sun, but close enough to be in its goldilocks zone. Is orbital speed purely a function of mass and distance? I'm guessing this means a year would be shorter than ours.
    It depends on the the star's mass but not the planet's; short answer is that for a red dwarf the year length might even be less than a week.

    Quote Originally Posted by EggKookoo View Post
    It had a small moon of its own (proportionately maybe the same as our own is to Earth) but it broke up and is in the process of forming a ring. That happened recently enough that there's still a cluster of mass, creating a lopsided ring, if that's at all possible.
    Why is it breaking up? If it reached the Roche Limit, and tidal forces are tearing it apart, then you might have what you describe... But it may or may not also result in the surface being constantly pummeled by debris, maybe enough to melt the crust. (You'd have to ask an expert.)

    If it was a collision, well that would for certain wipe out all life on the planet without extensive divine intervention, and there probably wouldn't be enough time for it to re-evolve before the ring stabilized into a new moon (or all fell to the surface).

    Biggest issue with rings is that your planet is small. Sure, it has the same surface gravity as Earth, but since the radius is a lot smaller so too is the total mass.

    Although, I remember reading a sci-fi story where an ultra-massive moon-sized object reduced its surface gravity to near earth-normal by artificial means, but went back up to what you'd expect at a distance. You could try that.

    I came up with another solution, below.

    Quote Originally Posted by EggKookoo View Post
    I want it to have an Earthlike atmospheric density at the surface, and it probably needs a magnetic field to keep that intact.
    The science isn't so certain about that. Looking at Mars suggests it is true, looking at Venus suggests the opposite, and we don't have enough exoplanetary data yet.

    But it would probably help. And since you can produce an extremely powerful magnetic field with a white dwarf or neutron star, that's one more point in favor of a degenerate matter core.

    Quote Originally Posted by EggKookoo View Post
    Given the size and gravity, how does that change the density gradient? How high up would you need to get to have top-of-Everest conditions in terms of thinness and temperature?
    I'm afraid I don't know.

    Quote Originally Posted by EggKookoo View Post
    The original construct is a single, smooth sphere that houses colossal alien machinery and whatnot. Over the eons, the surface has collected water and dirt and stuff from passing asteroids and comets (a process which may have been "helped" by its Sufficiently Advanced Creators, if necessary to get the amounts I need). This stuff built up to a layer ranging from maybe two miles thick to as much as twenty.
    Yeah, that's like half of the entire asteroid belt's worth of material, even before counting the gasses. Only way I see that happening is with a dedicated mining effort.

    Maybe somebody took a dwarf planet, and demolished it to cover the surface? With rapid terraforming and bio-engineering, they could put sapients on the surface before all the debris left in orbit as a temporary ring finished coellescing into a moon.

    Quote Originally Posted by EggKookoo View Post
    It eventually gets shaped and cleaned up by powerful entities into land and oceans. The landmass is a single belt that runs around the equator, about 500 miles wide (250 miles north and south of the equator, total area about the same as the 48 contiguous US states). I have this idea that there are passages deep underneath that allow the oceans to balance each other.
    You don't need them, water will either flow through aquifers or simply push the land more north/south to balance the oceans. Or it'll erode a channel of its own.

    Quote Originally Posted by EggKookoo View Post
    The poles are just ice caps, like the Arctic. The north and south oceans average maybe a couple of miles deep, but might have really deep spots here and there.

    This structure means no volcanoes or earthquakes, except maybe very tiny quakes as things periodically settle. There's also a dearth of ore, so refined iron/steel would be pretty hard to come by.
    If the surface is made from planetary debris, metals are going to be extremely common compared to earth. The only reason metals are as rare on earth as they are is because most of them (barring the lightest, like aluminum) sunk into the core back when the entire planet was molten.


    Quote Originally Posted by EggKookoo View Post
    Geology as a science would be weird, and unlike what we have here on Earth. I'm not sure geological layers would exist in any meaningful sense.
    Sure they would, only those layers would be purely sedementary and ejecta.

    Quote Originally Posted by EggKookoo View Post
    Along the center of the continental belt is a single mountain range that runs all the way around the world. I'd like the height of this to be roughly like Everest in terms of atmospheric density, but I'm not sure how high that would be. I assume the mountains would also interfere with winds and rainfall and such, but given the generally symmetrical layout of the continent, I'm not sure how that would work. Would both sides of the range see lots of rainfall? Would it vary by season? Speaking of seasons, the equatorial land arrangement seems like it would also mean there's little difference between spring and fall.

    The entities that shaped the landmass also seeded it with life, so if water flows "outward" (north and south) from the central ridge, there would be forests or at least some plains and whatnot. I don't know if there would be any sizable deserts anywhere, unless my configuration prevents much rainfall at all.

    So that's mostly it. The tl;dr of it is, how high should those central mountains be if I want them to feel like going up to the Himalayas, and how does precipitation work? And I guess, are there any gotchas I didn't think of?

    Thanks!
    I don't have much more time, so I'll just suggest that the mountain ranges could have been formed by the terraformers gently catching incoming material, as opposed to simply letting it crash into the planet.


    Quote Originally Posted by Martin Greywolf View Post
    Not even that. Kepler says t = 2*pi*sqrt(a^3*mu), where mu is gravitational constant and a is semi-major axis. So, the only thing that determines how long an orbital period is is how far apart the two objects are.
    The bolded bit is wrong.

    Mu is the product of the gravitational constant G and the mass of the major body (i.e. the sun for a planet, or the planet for a satellite).

    So, a larger sun means orbits with the same semi-major axis are faster. (But larger also means brighter, which means the goldilocks zone is father away, and the net effect is that earth-like planets' year length goes up the bigger the star is.)

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