Maps of rf₂ (or equivalently A_2, 0) for different assumptions on Phoebe’s interior structure. Crustal density is ranged on the y-axis and the rocky mantle density is ranged on the x-axis. The observed value of A_2, 0 to be matched is −6.11 ± 0.55 km and represented by the shaded bands. All cases include a rocky mantle and ice-rich layer whose densities are ranged (x- and y-axis, respectively). Models differ by the characteristics of an upper low density layer assumed as a megaregolith formed as a consequence of large impacts and long-term gardening with a density of 800 kg m⁻³ (right column) and 900 kg m⁻³ (left column) and varying thickness, from top to bottom: 10 km and 15 km. The white part are not consistent with available constraints (Phoebe’s density in particular).