Good size for a Planet?

Kaiser-Kun · Feb 4, 2009

The world where my novel takes place (called Eddeil), I can only imagine it as a really small world, but the events that take place are on a global scale. It's so small that you can go around it by train in a week, and has several small populations, but only three major cities, plus forests, mountains, deserts, and an ocean.

My question is, can such a world exist, and maintain a functional atmosphere, plus enough resources for its population, being so tiny? Or should I work to expand it? As I've imagined it until now, the plot only revolves around the places I mentioned, plus outside of the planet.

MumblingSage · Feb 4, 2009

I would say that's too small, simply because I imagine the planet would be smaller than Earth's moon (depends how fast those trains go, though), and therefore probably too small to maintain that atmosphere. Resources--depends on the size of the population. Picture a country you can travel across in a week by train. It could probably manage, but not well.

I would work on either A) Expanding it, or
B) making what you have now only a small part of the planet

B means having to move equators, poles, etc, which can be a headache, but sometimes it's the best option. I've had to do it before when in the writing process travel times suddenly became much sorter (therefore, places got closer to each other) than I anticipated.

As I sort of alluded to before, the other option is to make your trains really fast. Or to replace them with an extremely rapid form of transportation--planes could circumnavigate the globe in less than a week, for example.

Polenth · Feb 4, 2009

Or have the atmosphere artificially maintained in some way... which might be a good option if you want to keep the tiny planet feel.

kuwisdelu · Feb 4, 2009

I'd say it depends on how fast the trains go.

A sufficiently advanced race could sure make trains that travel several times the speed of sound. If they're willing to deal with the sonic booms.

Remember, though, give the planet itself a sufficient density and the size won't really matter as much. Titan is only about 50% fatter than Earth's moon and has an atmosphere more dense than ours. So I'd say your planet is perfectly possible.

A more dense planet might introduce other problems, though--it could have various mining, resource, and magnetic implications. But that's not necessarily a bad thing.

dclary · Feb 4, 2009

Why not go with a slightly smaller-than-earth planet, water world with only a tiny portion (about as much land mass as you could cross on train in a week) of arable land?

Kaiser-Kun · Feb 4, 2009

Thank you for your answers, I'm playing with some ideas right now. An idea ocurred to me about MumblingSage's suggestion,

B) making what you have now only a small part of the planet

:

There are two races in my novel, those with magic (Divira) and those without (Divira). Due to the obvious conflict, what if what I already have becomes a continent -which would be the place for the Divira-, and add a separate, say twice as big, continent for the Efira? I think that could triple the size of the planet and add another reason to the tension between both races. It could also add to the "Divira are extinguishing" feeling.

Most, if not all of the plot would take place in the Divira continent, tough.

semilargeintestine · Feb 4, 2009

Pluto, while no longer considered a full planet (although this would actually help your argument), has an atmosphere despite its small size. Compared to Earth's diameter of 12 756 km, Pluto is a dwarf (pun intended) at 2 274 km. Yet, when its orbit brings it close enough to the sun, the warmth evaporates some of the frozen Nitrogen, creating an atmosphere. It does not have a perpetual atmosphere, but that is a function of its distance from the sun rather than its size. If you give the planet the proper elements and keep it within the habitable zone of its star, the small size would not be a hindrance to its atmosphere (Mars is half the size of Earth, yet it has a fairly complex atmosphere, albeit a much thinner one than Earth).

Are the inhabitants of this planet humans? Are the trees like those on Earth? If so, you will have a hard time making the planet any different than ours, as changes in even one variable would dramatically affect life on the planet.

Chris Huff · Feb 4, 2009

Big enough to do what you need for your story, but not so big you have to fill it with people and places outside your story.

And the ships go the speed of plot.

Pthom · Feb 4, 2009

Of course, it could be completely improbable, such as Philip Jose Farmer's "River World". If you're writing some sort of fantasy (as opposed to hard SF), then I think you can do whatever is necessary to make the story work.

dclary · Feb 4, 2009

Kaiser-Kun said:
Thank you for your answers, I'm playing with some ideas right now. An idea ocurred to me about MumblingSage's suggestion, :

There are two races in my novel, those with magic (Divira) and those without (Divira). Due to the obvious conflict, what if what I already have becomes a continent -which would be the place for the Divira-, and add a separate, say twice as big, continent for the Efira? I think that could triple the size of the planet and add another reason to the tension between both races. It could also add to the "Divira are extinguishing" feeling.

Most, if not all of the plot would take place in the Divira continent, tough.

If they have magic, then it's not science fiction, and why do you care if the world is scientifically plausible?

End of question, make it what you want and go from there.

sirensix · Feb 4, 2009

dclary said:
If they have magic, then it's not science fiction, and why do you care if the world is scientifically plausible?

Grrrrrrrrrrrrrrrrrrrrr. For the nth time, "it's fantasy" does not mean that people who are interested in verisimilitude should be discouraged from doing research. Kudos to the Kaiser.

Kaiser-Kun · Feb 4, 2009

Well, I wouldn't like to answer "a magician did it" when (not if) I am told of a plothole in my story. Plus, it's important to the world to be able to sustain itself without magic and I might be saying too much here...

Pthom · Feb 4, 2009

However, "it's fantasy" does give the writer the opportunity to do things that are not scientifically plausable, technologically reasonable or listed in Wikipedia. Making stuff up does NOT give the writer the freedom to be inconsistant. And including magic isn't a requirement of fantasy, although it is frequently used to "explain away" those things that would otherwise be impossible.

sirensix · Feb 4, 2009

Pthom said:
However, "it's fantasy" does give the writer the opportunity to do things that are not scientifically plausable, technologically reasonable or listed in Wikipedia.

To me it just sounds condescending when one assumes that a person writing fantasy would be unaware of that "opportunity." If a writer is asking what would be realistic, it's a good indicator that she wishes for that portion of the world to be realistic. Otherwise, why would she be asking?

Most of the time, in my experience, the people who use "it's fantasy" as a deflection for those types of questions do not write fantasy, and are using the deflection as a subtle way of dismissing, or even expressing disdain for, the genre. I have seen that answer a LOT, because of my particular obsession with verisimilitude. Which is why my gut reaction when I see it (again and again and again) is "grrrrrrrrr." I want people to just ANSWER my question, or leave it alone, not tell me I shouldn't be asking it.

Unfortunately, to steer back on topic, I don't have any answers for the OP. I don't know anything about geology etc. - one of the major reasons I use an earthlike world. But I just wanted to say, good for you for asking the question, and don't let anyone convince you that science has no place in your work. I love that you care about that kind of thing, and I'd be interested to look at your work whenever it's in a state to be looked at.

Kazel · Feb 4, 2009

dclary said:
If they have magic, then it's not science fiction, and why do you care if the world is scientifically plausible?

End of question, make it what you want and go from there.

Even if a book has magic in it, that doesn't mean that the magic is such that it can affect things like how the planet holds onto the atmosphere. Maybe their magic is the ability to know the history of any item you touch. Its magic, but it doesn't necessarily affect the physical realities of the world due to its limitations.

As for size of the planet, the equation to discover a planets gravitational pull is M=(a*r^2)/G where M is the mass of the planet, a is the acceleration caused (the gravitational pull), r is the radius of the planet, and G is the gravitational constant. If your planet is dense enough, then it can have equal mass and equal gravitational pull to earth, and thus maintain an atmosphere. The niggly bits come in when considering whether there is a known substance thats dense enough for your purposes, whether that substance will allow for crop growth, ect ect.

Really though, once you know its possible, its up to you how far into actual science you want to go into for world building.

dclary · Feb 4, 2009

The question was:

My question is, can such a world exist, and maintain a functional atmosphere, plus enough resources for its population, being so tiny?

The answer, because it's a fantasy, is *yes.*

That's not a slam to people who calculate their worlds' specifications with 6-digit accuracy. That's not an insult to those of you mapping every continent on vellum parchment before writing word one.

It's just the answer to his question.

Stop trying to make life, and writing, so complicated.

Pthom · Feb 4, 2009

sirensix said:
To me it just sounds condescending when one assumes that a person writing fantasy would be unaware of that "opportunity." If a writer is asking what would be realistic, it's a good indicator that she wishes for that portion of the world to be realistic. Otherwise, why would she be asking?

Most of the time, in my experience, the people who use "it's fantasy" as a deflection for those types of questions do not write fantasy, and are using the deflection as a subtle way of dismissing, or even expressing disdain for, the genre. I have seen that answer a LOT, because of my particular obsession with verisimilitude. Which is why my gut reaction when I see it (again and again and again) is "grrrrrrrrr." I want people to just ANSWER my question, or leave it alone, not tell me I shouldn't be asking it.

Unfortunately, to steer back on topic, I don't have any answers for the OP. I don't know anything about geology etc. - one of the major reasons I use an earthlike world. But I just wanted to say, good for you for asking the question, and don't let anyone convince you that science has no place in your work. I love that you care about that kind of thing, and I'd be interested to look at your work whenever it's in a state to be looked at.

My apologies if my answer seemed condescending. I don't mean it to be. I do not assume that writers of fantasy are unaware of the opportuntites available to them. But it is my experience that often, people asking questions have not considered all of them.

Also, it is not apparent the story in question in the original post is a fantasy--in fact, on first glance, it looks very much like science fiction. Those responding before me have answered the question with science fact more than adequately. It had just occured to me that the story might work as a fantasy and not require the rigors of reality most SF writers demand.

I write mostly science fiction. But I am not opposed to writing less-than-rigorous speculative fiction, which might be termed science fantasy. Some folks may like it fine--others may think what I write is silly. In this community there is a wide range of styles, likes and dislikes, methods, and techniques. We get responses of all kinds, and it is likely some will be less than useful as an answer for the original question. But those answers might indeed be useful for someone else.

Lhun · Feb 4, 2009

Kaiser-Kun said:
Well, I wouldn't like to answer "a magician did it" when (not if) I am told of a plothole in my story.

Well then, the big question here is: is it really a plothole to have an impossibly tiny planet?
A magic universe can easily explain away the physical problems with it, and the only issue with consistency (read: unintended consequences) i see is that the stronger curvature might become important. I.e. on a much smaller planet the horizon will be closer. While height of observation point becomes more important. How high mountains can get depends on the athmosphere, climate and gravity. I.e. a small planet with conditions similar to earth otherwise could still have 10km high mountains.
Anyway, i suppose if you are worried about realism problems you should probably figure out if there is a reason not to simply let the story happen on a small continent (or two) instead of a small planet. Now i have only seen what you posted on this thread, but i don't see a reason why the planet has to be small.
It is easily imaginable to have a pretty much earth-like planet with 90% oceans instead of 70% to get a small landmass where the action happens. Or maybe most of the landmass hasn't been discovered yet and people think the planet is a disc. Or, when talking of fantasy it could *be* a disc.

Plus, it's important to the world to be able to sustain itself without magic and I might be saying too much here...

If you're not trying to let slip the fact that the vanishing or diminishing of magic is possibly a big point of your story... Sorry, too late.

MumblingSage · Feb 4, 2009

'A Little Prince' had ridiculously tiny planets.

However, it does depend on if the story has science fiction or fable-like sensitiblities. 'A Little Prince' is more of a fable than a modern fantasy story. On the other hand, you have Jenniver Fallon's 'The Lion of Senet,' which I thought, from reading the dedications and thank-yous to all the people who helped her research double-solar systems, was science fiction.

sirensix · Feb 4, 2009

dclary said:
That's not a slam to people who calculate their worlds' specifications with 6-digit accuracy. That's not an insult to those of you mapping every continent on vellum parchment before writing word one.

And that is neither condescending nor sarcastic. Also, very helpful to the original poster.

benbradley · Feb 4, 2009

There's "Mission of Gravity" which has a quite "improbable" planet with a few hundred gee's at the poles, and just two or three gee's at the equator, not because of its oblate spheroid shape, but because of its high spin rate. I don't even think the plant's possible origins are ever mentioned in the story, but the planet itself is an essential part of the story. The novel is widely considered a classic hard SF story.

A "small planet" with Earth-comparable gravity and atmosphere seems perfectly plausible, using something like a lead or even "depleted uranium" (u238) core. Perhaps a civilization hundreds of millions of years ago had a big stash of uranium, they separated out the 235 to use as fuel and tossed the 238 into this huge ball that over time became a generalized landfill-in-space, and the lighter elements floated on top of the heavier ones, and it eventually became a small planet (now I think about it, U238 becomes the more unstable P239 with just one neutron - I wonder if a big ball of U238 will eventually become a critical mass of P239).

sirensix · Feb 4, 2009

Pthom said:
My apologies if my answer seemed condescending. I don't mean it to be.

Thank you, I realize that now. I came into your response already irritated, which colored my perception when I made my first response. Sorry for sniping at someone who was actually trying to help rather than slam the genre.

Edit: I had a suggestion but the above post is actually cooler.

dclary · Feb 4, 2009

Lhun said:
Or, when talking of fantasy it could *be* a disc.

A discworld, eh?

Intriguing....

dclary · Feb 4, 2009

sirensix said:
And that is neither condescending nor sarcastic. Also, very helpful to the original poster.

Exactly. I'm glad we're on the same page finally.

Kaiser-Kun · Feb 4, 2009

I thank you all for your answers. I asked the question because I wanted my world to feel like a planet, rather than an isolated place.

The events that take place affect all of it, so I needed a small planet, but capable of having an atmosphere that permits life the way Earth does, small enough for my characters to travel without consuming too much time, but big enough to house several large cities and their populations, feed all those and at the same time give a "whole world consequences" feeling.

The approach I'm planning is more fantasy than sci-fi. If I had to look for a comparison, I'd say the world of Final Fantasy IX comes close, altough there's more technology in my world.

Good size for a Planet?

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