Minimum orbital intersection distance (MOID) for the nominal orbits of (525) Adelaide and (1270) Datura, numerically propagated backwards in time (at the abscissa of all panels). Top panel: general behaviour of MOID from 450 to 550 kyr ago. Zoom-ins on the periods shown in the grey rectangles (labelled a to c) near the minima of MOID are shown in the three middle panels, and provide the information at a greater time resolution. The same is repeated in the grey rectangles (labelled aa to cc) in the middle panels, and shown at still greater resolution in the bottom panels. The time in the middle and bottom panels is in years and in the top panel in kyr. The horizontal dashed line in all the panels shows the MOID = 10 km threshold.