Hydrogen abundance estimation model and application to (162173) Ryugu A. Praet, M. A. Barucci, P. H. Hasselmann, K. Kitazato, T. Iwata, M. Matsuoka, D. Domingue and B. E. Clark A&A, 649 (2021) L16 Published online: 02 June 2021 DOI: 10.1051/0004-6361/202140900