Today’s post is part of a bi-weekly series here on Planet Pailly called Molecular Mondays, where we take a closer look at the atoms and molecules that make up our physical universe, both in reality and in science fiction.
Imagine you’re a traveler in space, living in a time two or three centuries hence, engaging in the trade of resources between Earth, the Moon, Mars, and the asteroid belt. What is the rarest and most precious resource necessary for your survival out there?
You might think it’s oxygen, or perhaps water. Those are difficult resources to find in space, but not that difficult. A surprising number of asteroids do, in fact, have a surprising amount of frozen water on them or inside them. And if you can get water, you can easily split water molecules into hydrogen and oxygen through the magic of electrolysis.
No, of all the resources you absolutely must have to stay alive, the hardest one to find out there may actually be nitrogen. I first read about this nitrogen problem in a book called Asteroid Mining 101: Wealth for the New Space Economy, which says:
Nitrogen presents a more significant problem [than other essential resources]. Because of the great stability and high volatility of molecular nitrogen, it is poorly retained by solid minerals and poorly represented in meteorites.
Volatility, in this context, refers to the tendency of a chemical substance to turn itself into a gas. Planets and moons and asteroids (especially asteroids) have a really tough time holding onto volatile chemicals, also referred to as “volatiles.” And the closer a celestial body happens to be to the Sun, the more likely it is to lose its volatiles to the solar wind.
Your best bet for finding nitrogen in space would be the carbonaceous asteroids that tend to be found in the outer reaches of the asteroid belt. They’re a little bit farther from the Sun, and therefore have held on to their volatiles a little bit better. These carbonaceous asteroids are also one of the best places to go looking for water.
But according to Asteroid Mining 101, nitrogen has been found to make up only about 0.25% of the mass of carbonaceous meteorites, mostly in the form of organic polymers. “The figure of 0.25% is not very impressive […],” the book goes on to say (what an understatement of the problem!), but if you manage to capture a large enough carbonaceous asteroid, you could still potentially harvest a fair amount of nitrogen from it.
Of course if we were to imagine ourselves living in the even more distant future, in an era when humanity has expanded well beyond the asteroid belt, perhaps making it all the way out to the Kuiper belt, then nitrogen might not be such a ridiculously scarce resource. Based on what we’ve learned about Pluto and other Kuiper belt objects, it seems frozen nitrogen is a whole lot more common out there.