Current dynamics of Saturn’s spin axis according to its normalised polar moment of inertia λ. The value of λ (top horizontal axis) is linked to the current precession constant of Saturn (bottom horizontal axis) through Eqs. (3) and (5). The black interval shows the ‘instantaneous’ oscillation range of Saturn’s spin axis (i.e. without drift of α) obtained by numerical integration. The resonant angle is σ₃ = ψ + ϕ₃ (see Sect. 2). The green line shows Saturn’s current obliquity and resonant angle. The background colour indicates the type of past evolution as labelled in the top panel (see text for the numbering).