ARE TROJAN COLLISIONAL FAMILIES A SOURCE FOR SHORT-PERIOD COMETS

We have investigated the dynamical evolution of fragments generated by the impact breakup of Trojan asteroids, in order to study the formati on of collisional families in the Trojan clouds and to identify a poss ible genetic connection between these fragments and the population of short-period comets. Using a collisional model based on the results of high-velocity laboratory impact experiments and previously applied to main-belt asteroid families, we show that typical family-forming Troj an collisions eject a significant percentage (at least approximate to 20%) of the resulting fragments onto unstable orbits. Numerical integr ations of the orbits of such fictitious, unstable Trojan fragments sho w that soon they experience close encounters with Jupiter, and as a co nsequence they become undistinguishable from those of Jupiter-family c omets (some of which are currently close to the 1:1 Jovian resonance), of comets undergoing temporary satellite captures by Jupiter (such as P/Shoemaker-Levy 9), and of objects with Jupiter-crossing or -approac hing orbits (such as 944 Hidalgo, 2060 Chiron, 5145 Pholus and 3552 Do n Quixote). A reliable assessment of the efficiency of the transfer pr ocess from the Trojan clouds into comet-type orbits and of its time de pendence is difficult, owing in particular to the poorly known size di stribution of Trojans. However, an order-of-magnitude estimate suggest s that if the fragment flux from the Trojan clouds over the last appro ximate to 10(6) yr has been close to the average one over the solar sy stem's lifetime, then a few tens of the 160 known short-period comets might have been generated by Trojan collisions.