The requirement is enormous. Estimates put the nitrogen needed to build a workable buffer atmosphere at 2–3 × 10¹⁷ kg — hundreds of trillions of tonnes. There is no known Martian reservoir of that size. Nitrogen is not merely scarce on Mars; it appears to have been lost to space over billions of years, which is exactly what the absence of a magnetosphere predicts.
That leaves import. The large accessible reservoirs are Titan, whose atmosphere is overwhelmingly nitrogen, and Venus, which holds roughly four times Earth's entire nitrogen inventory. The delta-v costs are the problem: about 12 km/s from Titan and 15 km/s from Venus, applied to 10¹⁷ kg of gas. Moving that mass is an energy budget with no precedent in any human activity.
There is a local hint. Curiosity detected nitrates in Martian soil, and optimistic extrapolations suggest the planet-wide nitrate inventory could in principle yield a nitrogen partial pressure of a few tenths of a bar if fully liberated. That figure is an extrapolation from a handful of measurements, not a resource assessment, and thermally decomposing planet-wide surface deposits is its own industrial fantasy — but it is the only route that does not involve interplanetary freight.
The realistic answer, for now, is that nitrogen is why paraterraforming keeps winning the argument. A sealed habitat recycles its buffer gas; a planet does not. Covering a hectare needs a hectare's worth of nitrogen, and that is a shipment. Covering a planet needs 10¹⁷ kg, and that is not.
Saturn's largest moon carries a dense, overwhelmingly nitrogen atmosphere with low surface gravity — the single most convenient large reservoir in the solar system.
Curiosity confirmed nitrates in the regolith. A local source, even a partial one, removes the interplanetary freight problem from at least part of the requirement.
Buffer gas inside a pressurised volume is recycled indefinitely. The nitrogen problem is planetary-scale only; it barely constrains a base or a dome.
Two to three hundred trillion tonnes, moved across the solar system at 12–15 km/s. Nothing humanity has ever built approaches a millionth of this transport capacity.
The same solar-wind stripping that thinned the atmosphere took the nitrogen. Replacing it without first building a magnetic shield means refilling a leaking tank.
The often-quoted "0.3 bar from Martian nitrates" comes from projecting a few local measurements across the planet. It is a hypothesis, not a reserve.
A high-oxygen, low-buffer atmosphere is a combustion risk at every scale. Nitrogen is not optional for a breathable world; it is the majority of the air.
| Total nitrogen | 2–3 × 10¹⁷ kg | For a breathable buffer |
| From Titan | ~12 km/s delta-v | Plus the return logistics |
| From Ceres | ~8 km/s delta-v | Smaller reservoir, cheaper trip |
| Local alternative | Martian nitrates | Inventory unproven |
Nitrogen is the buffer gas. It dilutes oxygen so that a breathable atmosphere is not a fire hazard, and it supplies pressure without being toxic. Earth's air is 78% nitrogen; the Martian atmosphere is only 2.7% of a far thinner total.
The candidate reservoirs are Titan, Venus, Ceres and cometary bodies, at delta-v costs of roughly 8 to 15 km/s. Locally, nitrates detected in Martian soil are the only in-situ possibility, and their planet-wide abundance is unmeasured.
On the order of 2 to 3 × 10¹⁷ kg — two to three hundred trillion tonnes — to build a buffer atmosphere alongside the available carbon dioxide.
