Iron nitrite

Last summer this blog figured out that the limit on visiting an airless rock isn't oxygen, and maybe not even water so much; but inerts. Where this visitation is a settlement, nitrogen matters most. We've even attempted some equations. I didn't find much nitrogen in the Hebe class of stonies.

I was very aware that our asteroid-belt has a lot of ice - out by Pallas - coming to include ammonia, out by Saturnish 9 AU. I was skeptical that ammonia can survive ≤6 AU. Ammonia mixes with water and, together, lower the melting point so should steam out (maybe leaving the water behind). This, because we're always told of ammonia-water in Enceladus but not, say, Callisto. I want nearer-Earth asteroids first, and Deimos. I have little hope of ices particularly nitrogeniferous down here. Instead I mostly looked to cosmic charcoal.

Ryugu's samples are now suggesting that the meteorites we have on Earth from the C-class, like from Phaethon, might not be restricted to coal. Phaethon runs close to the Sun and other C here on Earth have blazed through our own atmosphere. These processes change the outside of the rock. At Ryugu, which remains cold, the processes have been enough to reduce iron compounds to pure iron. Iron compounds at Ryugu mostly mean magnetite rust. Ammonia will react with iron, releasing the ammoniac hydrogen. So the regolith - which we'll never see in a meteorite down here - contains a mix of leftover magnetite coated in Fe₄N.

The bad news is that Fe₄N is a layer around magnetite - and a thin one. To the extent the regolith adds to the total of nitrogen we figure upon stonies like, say, 6 Hebe - it doesn't add a very lot. Rather: this finding would show prospectors where to look first, to gather their nitrogen. Of course prospectors also get to keep that pure iron.