Top panel: osculating perihelion distance of (525) Adelaide’s nominal orbit (black) and the osculating aphelion distance of Mars (grey) vs. time into the past. Adelaide’s orbital behaviour is representative, at this level, of all members in the family. The arrows indicate epochs of local minima of Adelaide’s perihelion distance if ≤ 1.8 au during the past 700 kyr. Bottom panel: mean semi-major axis ā of six selected members of the Adelaide family: (452 322) 2000 GG121 in red; (475 474) 2006 SZ152 in green; (504 375) 2007 VV73 in blue; (517 580) 2014 UZ170 in cyan; (534 611) 2014 UC204 in magenta; and (545 614) 2011 SA45 in yellow. The mean value of the semi-major axis was obtained from the osculating value by digitally filtering short-period terms (periods ≤ 300 yr). The distinct jumps in ā correlate with the minima at the perihelion distance (therefore maxima of the orbital eccentricity), suggesting that shallow Mars encounters along with resonant perturbations are the responsible mechanism.