Outer belts capable of scattering material inwards at 10^-9 M_⊕ / yr after 100 Myr, around a G2 (1 M_⊙) star, with a chain of 1 M_Sat planets separated by 8R_H, that can be detected by Spitzer at 70 μm are shown in dark grey, whilst those belts that cannot be detected are shown in light grey. This is the lowest limit of the simulations shown in Fig. 4. The dotted line shows the maximum mass that can be retained against collisions (Eq. (5)) for 100 Myr and the dashed line shows the Spitzer detection limit for a G2 star. Full details of this plot are described in Sect. 4.3.