As amusing as this is, I feel compelled as a planetary scientist to emphasize that it is just shitposting.

We are almost certainly not going to be able to sustain an interplanetary human civilization with Earth as some sort of nature preserve & move all industry elsewhere. https://twitter.com/mutual_ayyde/status/1297036101438201857

The Moon doesn't have the resources to support any industry except mining specific minerals, & even that is suspect.

Asteroids may be more viable but they're so small it's unlikely we could make one a self-sustaining habitat w/o depleting its resources on very short time scale.

Mars? Mars is a whole bucket of unknowns.

We *already* have different groups of humans fighting over whether & how to terraform it, never mind that doing so (let alone doing so sustainably) is likely impossible & we really have no idea what the result would look like.

Humans on Venus pops up in hard sci-fi every so often, which is a shame b/c we actually know less about Venus than any planet in the Solar System, AND it's the best "Earthlike" exoplanet analog we have.

If *any* planet is going to be a "nature preserve" it should be Venus.

Anything more remote than that? Pure speculation, since permanent human activity at Jupiter & beyond will require propulsion, ECLSS, & just raw resources we can't currently access.

But this is mostly beside the actual point I want to make:

There has been a narrative for *at least* 30 years that when human civilization becomes interplanetary, we will do so by leaving Earth behind & learning to "live off the land," b/c of an assumption that it will be logistically impossible to supply a human presence from Earth.

That. Assumption. Is. Wrong.

Indeed I would personally be inclined to argue the opposite: it'll be impossible to sustain a human presence *without* logistical ties back to Earth.

You can use local resources where they're useful, sure, but they're *far* from everything you need.

But the logical extension of the perceived need to obtain all your resources in-situ is this sci-fi idea of moving all industry off-Earth, & that somehow Earth will become a net-importer (or even a total importer) of resources that are more scarce in space than they are here.

This strikes me as blatantly ignorant of what resources are actually available in space, not to mention basic economic ideas like comparative advantage, or an understanding of how trade has occurred in human history, or any recognition of how space would differ from that history.

Consider the easiest, most obvious example: food.

Nowhere in the Solar System could sustain agriculture except Earth. Never mind the chemical elemental abundances of their surfaces aren't suited for biology; they straight-up don't have soil! You can't grow plants in regolith!

If you want to have food on Mars, you either have to bring the food with you, or you have to bring soil with you.

And before you ask, no, Mark Watney would not have been able to make soil by mixing regolith, water, & poop. Soil is a LOT more complex than that.

Ok so we'd be relying on Earth for agriculture, but all the other industries can go elsewhere, right?

Nope. Not even close.

You could *maybe* have a sizeable metallurgical industry on other worlds, but that's a *very* small portion of our total industrial base.

Consider how much of our industry is reliant on either agricultural feedstocks or organic chemistry:

- textiles
- plastics
- polymers
- composites
- pharmaceuticals
- petrochemicals
- any industry which relies on the products of these, e.g.: mining, metallurgy, & manufacturing

And if you're thinking "well, can't we just find the raw materials for those in space?"

NO!

Nowhere else in the Solar System has coal, fossil hydrocarbons, or even fixed carbon! They all require biology to produce!

"But John, there's certainly *carbon* om other planets, right? Like Venus & Mars have CO2 atmospheres, & Titan's got all that methane & ethane, right? And didn't we find amino acids on an asteroid somewhere?"

Yes those exist, but good luck using them as industrial feedstocks.

Our organic chemical industry is *heavily* reliant on long-chain hydrocarbons that only exist on Earth, b/c synthesizing larger organic molecules from CH4 & C2H6 is *extremely* difficult & energy-intensive.

And if we had a good way to turn CO2 into hydrocarbons, we'd already be doing it on Earth as a climate change mitigation measure.

To think that we could readily do so on Mars or elsewhere is folly.

"But didn't The Case for Mars say we could use a Sabatier reacto-"

No.

To the extent that Robert Zubrin's argument has *any* merit, it's that by synthesizing methane from CO2, you could reduce the mass of propellant you need to bring from Earth on a human Mars mission.

That's NOT the same thing as saying we can do industrial-scale organic chemistry on Mars, *let alone* saying we could do so at the scale required to move all of Earth's industry to space.

Without invoking some truly revolutionary carbon-fixing technology, it's complete nonsense.

So basically, the thing to bear in mind is that while "industry" as a vague idea might exist in isolation from our day-to-day experience, it's fundamentally a deeply interconnected logistical system of moving resources around & combining/separating/modifying them to make stuff.

You really can't do that if some parts of the system are logistically isolated from others. Regardless of what resources we may or may not be able to obtain on other planets, none of them has everything we need, & none could sustain humans w/o a logistical connection to Earth.

Will there be differences b/w interplanetary trade & contemporary global trade? Yes! If nothing else, transporting stuff in space requires expending *way* more resources than on Earth.

But if anything that's just *one more* reason why moving all industry off-Earth wouldn't work.

B/c if you think it's hard for Earth to send stuff to space due to our gravity well, just think how much harder it would be if literally everything our species currently transports on Earth needed to be transported through space.

The propellant use alone would be unsustainable.

So yeah, sci-fi depictions of Earth being deindustrialized, depopulated of humans as we all migrate to space, & left as a nature preserve... just ain't gonna happen.

We can be more creative in how we imagine an interplanetary species.