Ammonium-bearing phyllosilicate grains detected in Ryugu and Bennu samples via infrared spectroscopy

Understanding the nature of nitrogen reservoirs in primitive small bodies is fundamental for tracing the evolution of volatiles in the early Solar System and their contribution to prebiotic chemistry. Here we report the identification, via infrared spectroscopy, of ammonium (NH4+)-bearing phyllosilicates inclusions in samples returned from carbonaceous asteroids Ryugu and Bennu. Typically hundreds of micrometers in size, they exhibit highly similar near-infrared spectral profiles in both collections, pointing to a generic formation process across this class of primitive objects. This process implies a chemical path that likely starts with highly soluble ammonium salts trapped in ices and mixed with anhydrous silicates, as detected on comet 67 P/Churyumov-Gerasimenko, and ends with ammoniated phyllosilicates, and a few less soluble ammonium salts such as the Hydrated Ammonium Magnesium Phosphorus-rich grains found in Ryugu and Bennu. These second-generation ammonium-bearing species were thus able to contribute efficiently to the delivery of nitrogen to terrestrial planets. Ammonium-bearing phyllosilicates are identified in Ryugu and Bennu asteroid samples. These stable phases may have transported essential volatiles across the solar system, offering a key mechanism for delivering life-essential elements to early Earth.