Saturn’s element abundances in the outer envelopes obtained with REOS3b for Case (I) (red open circles), Case (II) (blue solid circles), and Case (III) (black solid stars). Panel a: trade-off between heavy element and helium mass fractions in the molecular envelope. Panel b: trade-off between heavy element and helium mass fractions in the metallic envelope. We note that panel b applies to Y₁ ∕(X₁ + Y₁) = 0.180, but would remain very similar for the other Y₁∕(X₁ + Y₁) values.