THE DISRUPTION OF HYPERION AND THE ORIGIN OF TITANS ATMOSPHERE

Two peculiar features of the Saturnian satellite system, that is, the dense, N-2-dominated atmosphere of Titan, and the very irregular shape of Hyperion, are probably related to each other. Numerical integratio ns show that most fragments ejected after the catastrophic breakup of a presumably larger and nearly-spherical proto-Hyperion fell onto Tita n over a time scale of 10(3) yr, at impact speeds <4 km/s. Such impact s resulted into accretion of the constituent volatile materials into T itan's atmosphere. If proto-Hyperion was approximate to 1000 km in dia meter, the entire current atmosphere may have been generated by this i mpact shower. Even for a smaller total mass of the impactors, any pre- existing atmosphere must have been chemically reprocessed, producing l arge amounts of N-2 by shock effects. Impacts by proto-Hyperion fragme nts are also likely to have formed giant impact basins on Titan's surf ace. (C) 1997 American Astronomical Society.