Properties of icy grains as a function of size. (a) Grain temperature. (b) Grain velocity computed assuming a CO production rate of 4 × 10²⁸ s⁻¹ emitted in a cone with a half-angle equal to ψ = 45° (dashed curve) or ψ = 180° (solid curve), and a dust and nucleus density equal to 500 kg m⁻³. Velocities in the gray region are excluded at 1σ from the velocity offset of the H₂O and HCN lines. (c) Grain-sublimation lifetime; the two horizontal blue dotted lines correspond to the elapsed time between the 16.05 April 2010 outburst and the Berschel H₂O observations. (d) Scale length defined as the product of the grain-sublimation lifetime times the grain velocity (calculated with ψ = 45°); the horizontal line corresponds to the limit of CO free-molecular flow (see text). In panels a, c and d the black and red curves correspond to crystalline ice mixed with olivine and carbon, respectively. Solid and dashed lines show ice-poor grains (v_i = 0.5, ice mass fraction of 29%) and ice-rich grains (v_i = 0.1, ice mass fraction of 78%), respectively.