The silliness of Star Wars’ single-climate planets

Single climate worlds are all through the Star Wars universe – worlds that, inexplicably, have a single ecosystem – ice, desert or forest, usually.

The Embassy Theatre, Wellington, December 2015 - where Sir Peter Jackson premiered 'The Hobbit' and the third 'The Lord of the Rings' movies.
The Embassy Theatre, Wellington, December 2015 – where Sir Peter Jackson premiered ‘The Hobbit’ and the third ‘The Lord of the Rings’ movies.

Yet they’re all habitable by humans. I can see where the idea comes from. Here on Earth we often travel from one climate to another. Islands, particularly, often have a single ecosystem – tropical, for instance.

Crank that up into space and you have the Star Wars model. It was also used in the 1980 Flash Gordon movie where the Moons of Mongo (floating, inexplicably, in Mongo’s atmosphere) were inevitably single-climate locations. Alas, science says things are a bit different when you get up to world size.

Any world habitable by humans and as closely Earthlike as the Star Wars worlds (including Tatooine, which appears to be exactly like the Tunisian desert near the town of Foum Tataouine) would also have a variety of ecosystems that suit its cold, temperate and hot zones, just like Earth. The specifics would vary, but the general principle can’t because it’s a function of physics.

Of course we can’t complain too much. Star Wars was never ‘science’ fiction – it was always a rollicking adventure yarn that happened to be set in a galaxy far, far away, and was all the better for that too.

The Masonic Hotel (1932) - early streamline moderne, with the former T&G Building (1936) behind.
Trapped on the stylish all-deco moon, Flash sought refuge in a streamline moderne hotel, thanking his lucky stars he wasn’t caught in the Swedish Modern World.

The main problem for me, though, is the ‘planets are like islands on Earth’ model.

If we want to write ‘science’ fiction, surely the action will be set on worlds that are different – maybe very different.  I’m particularly thinking of Mesklin from Hal Clement’s A Mission of Gravity (1953) He imagined a rocky world with twice the mass of Jupiter, but with a 17-minute ‘day’ – spinning so fast it’d lost its spherical shape and bulged out at the equator. The technical term is ‘prolate oblate spheroid’. We have one in the Solar System – Haumea, a Kuiper Belt Object that looks like a football on the back of its spin-rate.

At Mesklin’s equator, partly thanks to centripetal effects from that incredible spin, surface gravity is 3 Earth gravities. At the poles, it’s 700. Don’t try to stand up, OK?

Haumea. A picture I made with my trusty Celestia installation p- cool, free science software.
Haumea. A picture I made with my trusty Celestia installation – cool, free science software.

Technically, gravity (a second-order effect of space-time distortion) behaves as a point-source and its strength is inversely proportional to distance from the centre of mass. Thus, although Earth’s gravity is produced by every particle that comprises the Earth, everything is pulled towards the centre of the planet – ‘down’. If the Earth was less dense and had a greater radius, surface gravity would be lower for the same mass.

On Mesklin, the poles are way closer to the centre of mass than the equator, hence the surface gravity is far higher. Clement initially came up with two values for the polar pull – 655 and 700 g. The thing is, gravitational pull isn’t smooth: mass concentrations invoke local variations. That’s clear on our own Moon, particularly, where ‘mascons’ affect the orbits of satellites.

In the case of Mesklin, the mass in the equatorial bulge would be sufficient to do so on a much larger scale, affecting local gravitational pull. Just so you know, the equation for calculating the surface gravitation of a prolate oblate spheroid is:

Gravity EquationWhere p is the density (assumed to be constant), a is the semimajor axis and c the semiminor axis, G is the gravitational constant 6.674×1011. And pi, of course, is pi… (well…?) Oh, you calculate k with this equation:

Here’s some more info on it.

Yah – that’s why everybody (especially in the age of pen, paper and slide rule) kept coming up with slightly different answers… And, indeed, Clement later recalculated the polar pull to be just 275g. That didn’t affect his plot, of course. But Mesklin, really, was a think-experiment that allowed for a brilliant plot (which I won’t spoil, if you haven’t read the book).

EW Vol I Cover 2 200 pxWhat I am getting at, though – and the take-home lesson – is that by infusing a bit of ‘science’ into the science fiction, we can create some wild and amazing places that get away from the ‘island metaphor’ – and which simply beg to have amazing stories written about them.

If you want to see how I’ve applied that in practise, check out my novella ‘Missionary’ – one of seven stories by seven great authors in the first Endless Worlds compilation. Out on Kindle and in paperback.

Copyright © Matthew Wright 2016


13 thoughts on “The silliness of Star Wars’ single-climate planets

  1. I think sillier than the whole ecosystem bit was the oxygen-everywhere idea. At least in Dune, they had to wear converters for breathing. But then again, Star Wars is just space fantasy. When Lucas did try to inject some science-sounding stuff into the movie plots, it didn’t go so well. I think, maybe, there’s also just this idea, because we see planets in our own solar system that are basically one hue, we think there’s some sort of blanket descriptor for them…. this holds true for every planet except Jupiter, which, due to the Eye and stripes, people can imagine with more “action” going on under the surface.

    Can you really work out that entire formula? Kudos to you…. I wouldn’t have the patience!

    1. I haven’t tried either! I actually did a lot of maths to nail some of the numbers and credibly scene set a sf novella I wrote last year. But that was orbital periods, velocities and centripetal acceleration (my starship had a spinning hab module) which is waaaaaay simpler than the equation here. I wouldn’t try to solve it…

      1. Okay… well, that makes me feel a little better. I didn’t sleep through my math and science classes, but shoot…. 😛 There’s another blogger I know who loves doing all this minute detail stuff with her SF. Maybe you would enjoy following each other. Jeno Marz (

  2. Well, to defend the single-ecosphere-planet thing …

    To an Earthling’s point of view, Mars and Venus seem like they have the one weather system each. A Martian or a Venusian would be much more sensitive to the differences, certainly, in much the way (say) someone living in Singapore — where the temperature, light, and humidity are basically the same every day — can tell the difference between February and July just by how they feel.

    And for a more solid defense, in the main, Star Wars trips to a planet are just to one spot, or one area, of a planet. If they never get more than ten miles from the initial contact point it isn’t unreasonable things look pretty much the same. You can write off something like “a forest moon” as “well, it’s got about twice the temperate forest area of a typical moon, which isn’t to say it hasn’t got ice caps and stuff, just, it’s got a lot of forest”.

    1. I have a distinct memory of being caught in a tropical downpour one afternoon on Clark Quay. That is my main memory of Singapore weather… I agree that a planet which to us looks one climate might well have subtle variations. And a place with more forest might appear as a ‘forest world’ (New Zealand was, up until the end of the 13th century). My only gripe is that SW planets were never quite that finely drawn…

  3. I like the idea of an entire planet which you could describe as “tepid”. That’d be a fun place to live.

    Inexplicable is my favourite word at the moment and it sums up Star Wars rather perfectly, although I do like the franchise (apart from the horrendous prequels).

  4. Excellent post! And you’re spot on about the reasoning behind the Star Wars planets — the science wasn’t important, the story was. I admit to being guilty of this myself in my “sci-fi” books (more space opera than anything else, lol). I try to throw in some wacky science stuff from time to time, but most of my focus is admittedly on my characters and the shenanigans they get up to.

  5. I hope you’ll forgive me for not poring over those equations in detail. Still, I understand enough “executive level” science to agree wholeheartedly. Star Wars is more fantasy than science. I fantasy plot taking place in space. So the overly simplistic worlds are no surprise. I love the details on gravity. I think I must play with that in any upcoming stories.

    1. I’ll look forward to reading them! Yes, Star Wars is a rollicking good yarn and the idea carries some great story potential for the future spinoffs… but ‘science’ fiction it ain’t.

Comments are closed.