Rotational dynamics of subsolar sublimating triaxial comets

A model with subsolar water sublimation on a triaxial, ellipsoidal comet nucleus is presented for the calculation of reactive torques. The resulting differential equations describing the cometʹs rotation are then Hamiltonian, and gravity-gradients are trivial to include. While effects derived from a weak perturbing function are neither able to change the rotational excitation nor the spin magnitude of the nucleus, it is shown how the spin orientation of comets can change significantly over an orbital run. However, of the four comets studied, 1P, 19P, 46P and the Rosetta target 67P, 19P and 46P were the only objects clearly exhibiting this feature, thereby confirming a technique used to derive the consequences of a more elaborate model of sublimation induced torques. In particular, the rotational parameters of 67P were seen to be very stable, indicating that a highly kinematical model of its rotation for the mapping of the cometʹs gravitational field during the Rosetta mission can be used. The modelʹs hierarchy with 1P/Halley as the object with highest excitation probability, is consistent with observations.