Phase-space distribution of grains of three different sizes for a disc with a belt eccentricity e_b = 0.4: (top) s = 38 ?m (β = 0.06), (middle) s = 8.3 ?m (β = 0.26), and (bottom) s = 4.3 ?m (β = 0.5). The radial coordinate is logarithm of eccentricity, while the longitude of periapse ϖ is plotted azimuthally. The colour scale indicates mass per unit mass, eccentricity, and angle. The two columns of panels represent (left) the initial stage at t ≈ 0 yr and (right) an intermediate stage at t = 10⁷ yr. The black crosses indicate e_b. The light blue dots indicate orbits of fragments that are launched in equidistant steps of true anomaly from a parent belt with zero relative velocities; the spread of blue dots around black crosses represents the result of radiation pressure; see Sect. 3.3. White lines in the top panels roughly enclose the initial distributions in the parent belt (i.e. the assumed spread Δe_b of parent body eccentricities around e_b).