Viscous stirring for bimodal mass distribution. The figure shows root mean square eccentricity (top panel) and inclination (bottom panel) of a ring of planetesimals with bimodal mass distribution. There are 800 planetesimals with mass 10²⁴ g (component 1, m₁) and 200 with mass 4 × 10²⁴ g (component 2, m₂). The ring is centred at 1 au and the surface density is 10 g cm⁻². Shown are the results of our model (orange), a full N-body simulation with mercury (grey), and the semi-analytic model of Ohtsuki et al. (2002; black dashed). Component 1 and 2 are indicated with solid and dotted lines, respectively.