(Left) Time evolution of rotational period change for SHAPE-SYN and SHAPE-REV assuming current Arrokoth obliquity. The SHAPE-REV body experiences stronger changes in spin period by about two orders of magnitude during simulation because it’s more asymmetrical compared to the SHAPE-SYN (see also Supplementary Fig. 5). (Right) simulations done for SHAPE-REV for two cases of obliquity close to 90° in which case the spin period does change considerably slower, at change of ~10−5 hrs after 0.6 Myr. Here, combined with the result shown in Supplementary Fig. 5, we can conclude that if the external gravitational torque from planet encounters could be ignored1,3, then the spin state of Arrokoth didn’t change appreciably during its evolution history even when taking sublimation torques into consideration (under the assumptions of homogeneity).