In the lowmass planetary systems, the fraction of stable zones between pairs of outer giant planets that contain at least one planetesimal on a stable orbit as a function of the mass of the outermost giant planet (left panel) and the width of the stable zone Δ in units of mutual Hill radii (right panel). For the left panel, bins were evenly logarithmically spaced from 10   M_⊕ to 1   M_J. For the right panel, bins were evenly spaced from Δ = 3.5 to 30. The error bars were calculated using binomial statistics following Burgasser et al. (2003). The dashed line marks the two planet stability boundary (Marchal & Bozis 1982; Gladman 1993).