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R. Canup (Southwest Research Institute), E. Asphaug (University of California Santa Cruz)
While an impact-triggered formation of the Pluto-Charon system is favored (see review by Stern, McKinnon & Lunine 1997), this scenario has yet to be quantitatively tested through impact simulations. Unlike the relatively well-constrained situation for the formation of Earth's Moon, key properties of Pluto and Charon - their rock/ice fractions, mass ratio, and total system angular momentum - are still somewhat uncertain. However, a primary challenge is obtaining a sufficient yield of material in bound orbit: Charon likely contains ~10% of Pluto's mass, whereas the Moon has only ~ 1 simulations involving rocky objects have found a maximum yield of material placed in orbit of only ~ 3 to 4% of the total colliding mass (Canup, Ward & Cameron 2000).
Here we report results from a suite of smoothed particle hydrodynamics (SPH) simulations designed to explore what types of impacts (e.g., impact velocity and angle, impactor size) involving various types of objects (differentiated or not; silicate rich or not) might produce the very high yield of orbiting material required to form Charon. Reliable equations of state for candidate materials are a requirement for any such model, and some (water ice) are still under development; here we utilize the ANEOS equation of state (Thompson & Lauson 1972). Previous results (Canup & Asphaug 2001) of Moon-forming impacts suggest that for impacts occurring at the mutual escape velocity, the fraction of material placed into orbit will be greatest for colliding objects that are close in size. However, the high angular momentum of the Pluto-Charon system also allows for higher velocity collisions from smaller objects, and such cases will be also be simulated.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.