So… can we import nitrogen from somewhere else? Are there types of asteroids which are high in nitrogen? What about the gas giants and ice giants, and their moons? Any nitrogen there we could just… yoink?
Yes, but again, if we are doing this only to shed it into space (on a terraformed mars), then we are importing it to Mars to reduce the total load bearing capacity of the solar system in the future.
Furthermore, you have to spend the colossal amounts of energy to move atmospheres worth of nitrogen around the solar system.
There is a small irony that nitrogen is currently used as gas thrusters for rockets. We’re dumping earth’s nitrogen into space already, granted in very very small amounts. But harvesting the earth’s atmosphere for nitrogen would be very bad in the longer term if done in bulk.
Pure N2? Probably rare. The solar system does have a shit ton of ammonia though, so thats a great source of nitrogen that can be broken down to get what we need.
I’d argue phosphorus is an even more limiting compound.
It is a regular enough mineralogical component in martian regolith. If we use the soil to grow things, we should be fine as is. Furthermore, we aren’t worried about losing it into space if we terraform.
On the scale of the solar system, phosphorus may indeed end up being rare and might be one of the limiting factors for total load bearing capacity of the solar system.
