Peas in a pod: spacing. The plots shows the period ratio of the outer pair of planets as a function of the period ratio of the inner pair for the underlying population (left), for the underlying population of detectable planets (middle), and for the KMPS systems (right). The dashed horizontal lines mark some of the important commensurabilities. The number inside the parenthesis is the percentage of outer planetary pairs that have a period ratio within 1% of the indicated commensurability.