Did the Hilda collisional family form during the late heavy bombardment?


E-mail: mira@sirrah.troja.mff.cuni.cz


We model the long-term evolution of the Hilda collisional family located in the 3/2 mean-motion resonance with Jupiter. Its eccentricity distribution evolves mostly due to the Yarkovsky/YORP effect and assuming that (i) impact disruption was isotropic and (ii) albedo distribution of small asteroids is the same as for large ones, we can estimate the age of the Hilda family to be 4+0−1  Gyr. We also calculate collisional activity in the J3/2 region. Our results indicate that current collisional rates are very low for a 200-km parent body such that the number of expected events over gigayears is much smaller than 1.

The large age and the low probability of the collisional disruption lead us to the conclusion that the Hilda family might have been created during the late heavy bombardment (LHB) when the collisions were much more frequent. The Hilda family may thus serve as a test of orbital behaviour of planets during the LHB. We have tested the influence of the giant-planet migration on the distribution of the family members. The scenarios that are consistent with the observed Hilda family are those with fast migration time-scales ≃0.3–3 Myr, because longer time-scales produce a family that is depleted and too much spread in eccentricity. Moreover, there is an indication that Jupiter and Saturn were no longer in a compact configuration (with period ratio PS/PJ > 2.09) at the time when the Hilda family was created.