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[20.12] Constraints on Collisional Evolution in the Edgeworth-Kuiper Belt: Exploiting the ``Vesta Crust'' Paradigm

D.D. Durda, S.A. Stern (SwRI), J.I. Lunine (UA/LPL), A. Morbidelli (Obs. Nice)

In the asteroid belt, the survival of Vesta's basaltic crust after 4.5 Gyr of collisional evolution provides a key constraint on the amount of impact processing that has occurred. By analogy, we extend this constraint to the Edgeworth-Kuiper Belt (EKB), employing Pluto's volatile N₂/CO/CH₄ crust in much the same way. (Smaller EKB objects are most likely not able to provide additional constraints, since they are unlikely to differentiate [Stern 1989] and thus obtain a crustal veneer of volatiles, and even if they did, volatiles are rapidly lost owing to intense hydrodynamic escape [Trafton et al.~1987]). Using an established EKB collision model (Durda & Stern 2000), we find that in the present-day collisional environment, some 1--2\times10³⁰ ergs/Gyr of impact energy are deposited on Pluto, corresponding (for a pure N₂ crust) to some 60--120 m/Gyr of impact devolatilization over 4 Gyr. This loss, perhaps 0.2--0.5 km, is small compared to the estimated 10--40 km maximum depth of Pluto's N₂ crustal veneer. However, during the early, massive EKB epoch, which lasted perhaps ~0.3--1.5 Gyr (Stern & Colwell 1997), we estimate that up to ~18~km of crustal N₂ could have been devolatilized. We will discuss the implications of impact devolitilization for constraints that may be placed upon the timing of Pluto's crustal differentiation, the amount of N₂ in Pluto's crust, the mass of the early EKB, and the duration of the massive EKB era.