Lower limit of dust-to-ice ratio as derived by the dusty-ice thermal model. The blue curve describes the icy area fraction (x-axis) as a function of the assumed dust-to-ice ratio (y-axis). The black squares indicate the modeled dust-to-ice ratios, derived from the modeled water ice erosion as a function of the assumed icy area fraction. The intersection of the two curves indicates a consistent estimate of the dust-to-ice ratio.