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.

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.

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 – 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:

Where p is the density (assumed to be constant), a is the semimajor axis and c the semiminor axis, G is the gravitational constant 6.674×10⁻¹¹. 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).

What 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