KBO binaries: are they really primordial ?
Résumé
Given the large orbital separation and high satellite-to-primary massratio of all known Kuiper Belt Object (KBO) binaries, it is important toreassess their stability as bound pairs with respect to severaldisruptive mechanisms.Besides the classical shattering and dispersing of the secondary due to ahigh-velocity impact, we considered the possibility that the secondary iskicked off its orbit by a direct collision of a small impactor, or that itis gravitationally perturbed due to the close approach of a somewhat largerTNO.Depending on the values for the size/mass/separation of the binaries thatwe used, 2 or 3 of the 8 pairs can be dispersed in a timescaleshorter than the age of the solar system in the current rarefiedenvironment.A contemporary formation scenario could explain why we still observe thesebinaries, but no convincing mechanism has been proposed to date.The primordial formation scenarios, which seem to be the only viable ones,must be revised to increase the formation efficiency in order to accountfor this high dispersal rate.Objects like the large-separatioKBO binary n2001~QW$_{322}$ must have beeninitially an order of magnitude more numerous.If the KBO binaries are indeed primordial, then we show that themass depletion of the Kuiper belt cannot result from collisional grinding,but must rather be due to dynamical ejection.