a) Contours of midplane solids-to-gas ratios (black) as function of the turbulence parameter α and the solids-to-gas accretion rate ℱ_{s / g}. The gas accretion rate Ṁ_gas is fixed to 10^-8M_⊙yr^-1 and the initial size of the pebbles τ₃ is fixed to 0.03. Orange contours denote the amount of solid material (in Earth masses) that is required to form the eventual peak in the ice surface density just outside the snowline. b) Contours of midplane solids-to-gas ratios as function of α and Ṁ_gas. The solids-to-gas accretion rate ℱ_{s / g} is fixed to 0.4 and the initial size of the pebbles τ₃ is fixed to 0.03. Orange contours denote the amount of solid material (in Earth masses) that is required to form the eventual peak in the ice surface density just outside the snowline. The cyan lines denote a Toomre parameter (Q_T) of unity at 10 au (1 au); the space below these lines has Q_T< 1 and is gravitationally unstable at 10 au (1 au).