Planet of Haberdashers

Mining planets. Prison worlds. Agricultural colonies. Science fiction seems to be full of planets with only one industry. As a trope, it’s similar to the Planet of Hats, but instead of the aliens all sharing the same single defining characteristic, it’s their economy. Doctor Who features a library planet, and so does the Foundation series – plus the latter has Trantor, a planet that is literally nothing but the capital city. In Dune, Arrakis doesn’t seem to produce anything but Spice, and as a bonus, it’s a Single Biome Planet. Farscape has that planet where everyone’s a lawyer. And so on. The problem is, it’s nonsensical.

An image of two humanoid Edo, from Star Trek: The Next Generation

Star Trek: TNG is full of examples, but the one I’ll never forget is the Planet of Oversexed Aerobics Instructors.
Image via Memory Alpha

The theory behind single-purpose planets seems to be rooted in the idea of comparative advantage - that each planet will specialize in whatever they’re best at (library science, assassination) or have the most of (unobtainium, arable land) or have a monopoly in (drugs, aerobics instructors) and focus on that industry to the exclusion (or near-exclusion) of all others, exporting huge quantities of it and importing everything else in turn. But that’s not even how international trade works on this one planet we’ve got right here. For most countries, trade is a very small part of their economies – under 10% for two-thirds of them, with only a handful seeing numbers higher than 25%. Furthermore, most countries produce more than one thing for export. But the lion’s share of every country’s economy is inwardly-focused – producing and selling goods and services to be consumed by its own citizens. They have to – their workers can’t go on mining unobtainium or producing widgets unless they’re fed, clothed, housed, and someone’s there to fix the toilet when it plugs up. Unless you’re planning on calling a plumber from the Roto-Rooter system, I guess.

A 2008 article in Astropolitics outlines several more problems for our fledgling hairdressing colony. The cost of transporting goods over interstellar distances* means that anything so traded will be either extraordinarily valuable or intangible – information, in other words. And the time it takes to traverse those distances means not only that nothing perishable is likely to survive the trip, but that the price at which you can sell your goods may have changed significantly while you were in transit.

Finally, as Paul Krugman pointed out in his 1978 paper on interstellar trade (highly worth a read, despite its ostensible focus on some rather dry mathematical analysis), the opportunity cost of being an interstellar trader is really high. If you have multiple-year round trips (or up to several hundred years, lacking faster-than-light travel), the potential profits you anticipate need to be equal or better to the money you could have made by staying home and investing the cost of the trip locally. Agricultural exports and common minerals aren’t going to cut it, even if the food did keep until your next port of call.

If you’re writing about populated planets that aren’t Earth, you probably don’t need to generate sector-by-sector industrial reports, or tell us what the unemployment rate is for marginally-attached spaceship hull manufacturers. But it’s good to keep in mind that planets are, well, planets - and that treating them like really big mining towns or farming villages impoverishes your worldbuilding for those places.

*Unless one posits advances that make the construction and operation of arbitrarily large ships extremely inexpensive, ideally at faster-than-light speeds. But in a universe where human technology has progressed that far, why would we bother shipping doodads back and forth?

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