Image: © MNHN - J.-C. Domenech
On May 14th 1864, a meteorite fell south of Montauban (France). It exploded into multiple fragments, most of which were collected in the town of Orgueil, giving it its name: the Orgueil meteorite.
This meteorite is rare (only 9 samples of this type) and exceptional in many respects, but its unique chemical composition, similar to that of the Sun, makes it one of the most primitive materials in our Solar System.
The chemist Stanislas Cloëz (1817–1883) was one of the first to analyze the CI Orgueil in 1864, and found among several substances, the presence of ammonium chloride (NH4+Cl-). Ammonium acts as a significant carrier of nitrogen in the Solar System, and is linked to the formation of more complex organic molecules, which are fundamental to prebiotic chemistry. However, the extraterrestrial origin of the NH4+ in the Orgueil was not confirmed by isotopic analysis (𝛿15N).
In this study, we investigated the nitrogen content and isotopic composition of ammonium in the Orgueil meteorite. We found that NH4+ in Orgueil has an extraterrestrial origin, showing specific nitrogen isotope ratios enriched in 15N compared to Earth's atmospher (δ15N = +72 ± 9 ‰). Ammonium in the Orgueil meteorite possibly exists as inorganic and organic salts, as well as ammoniated phyllosilicates. The nitrogen in Orgueil is distributed among organic matter (~35%), ammonium (~30%), and a significant portion that remains unidentified to date (~35%).
The presence of ammonium in the Orgueil meteorite could have been produced via heating and/or aqueous alteration processes of organic matter, or from the accretion and/or later deposition of NH₃ ice, NH₃ hydrates, and/or NH₄⁺ salts in the asteroidal parent body.
Ammonium has also been found on Ceres and comet 67P/Churyumov-Gerasimenko, and it might exist on many other small bodies in space. If these ammonium salts were originally in the Orgueil meteorite, they could have been lost during its entry into Earth's atmosphere or shortly afterward. This means that the parent body of Orgueil may have contained even more nitrogen in the form of ammonium.
Paper: https://www.sciencedirect.com/science/article/pii/S0016703724005180?via%3Dihub