Thermal inertia as a function of grain size R and porosity (color coded) at T = 80 K, emissivity ϵ = 1 for crystalline (full line) and amorphous (dotted line) ice forms. Top panel: tight contacts ((G+JKR)+BB combination) Bottom panel: loose contacts (W+BB combination). Colors correspond to increasing porosity, from p = 0.26 (black), p = 0.5 (red) to p = 0.84 (orange). Constraints on Mimas thermal inertias in region R₁ (dot-dash line, Γ₁ ≤ 16J/m²/ K/s^1/2) and region R₂ (dashed line, Γ₂ = 66 ± 23J/m²/ K/s^1/2) provided by Howett et al. (2011) are also plotted (see Sect. 3.2). Vertical line denotes R = 1 mm.