Posterior of the ratio of Fe over Mg in the atmosphere of WASP-121 b from retrieval results. The blue point is the median of the blue distribution, with the error bars being the 1 σ uncertainties of that same posterior. The yellow and red areas respectively represent the 1 σ uncertainties of the Fe/Mg for the Sun (Asplund et al. 2021) and WASP-121 (Polanski et al. 2022). The retrieved ratio is consistent with both the solar and stellar value.