Fluorine in the late fluids of asteroid RyuguOPEN ACCESS 

R. Conconi, C. Le Guillou, S. Laforet, M. Marinova, H. Leroux, L. Jossé, A. Aléon-Toppani, Z. Dionnet, R. Brunetto, S. Bernard, B. Dazas, A. Miyake, T. Noguchi

Geochemical Perspectives Letters, V. 42, Published 22 October 2026

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“Fluorine is a highly reactive halogen whose distribution and speciation may provide key insights into fluid evolution and element mobility in planetary materials. Yet, despite its cosmochemical significance, the phase carrier(s) of fluorine, its speciation and behaviour during fluid-rock interactions are still enigmatic. Here, we report the occurrence of fluorine associated with phyllosilicates at the nanometre scale in Ryugu samples. We carefully evaluated the possibility of exogeneous contamination, but several lines of evidence indicate that fluorine is most likely indigenous. It is concentrated in particular in saponite, possibly via OH-F substitution, and/or as interstitial fluoride salts. These observations are interpreted as the result of fluorine release from primary carrier(s) and its subsequent concentration within late stage, highly saline fluids. Limited phosphorus and sodium availability likely restricted apatite, Mg, Na phosphates and Na carbonate formation, preventing them from acting as a major sink for fluorine and favouring its retention within phyllosilicates. This finding expands the scope of previously documented brine related mineral assemblages in Ryugu and Bennu and reveals an unexpected behaviour of halogens in primitive Solar System bodies.”