We combine experimental data and theoretical results to develop a model for the changes in the rotation rates of fragments produced by large collisions that break up and disperse asteroidal targets. Collisions that partially disperse the target can also produce a despinning of the reaccumulated core due to the angular momentum "splash" effect arising from the preferential escape of material with higher than average angular momentum (Cellino et al. 1990, Paper I). Combining these results with previously published work on spin rate changes for cratering impacts (Harris 1979; Dobrovolskis & Burns 1984), we present a comprehensive model for the changes in asteroid spin rates due to collisions. This spin change algorithm, when incorporated into an existing simulation of collisional effects on asteroid sizes, produces an integrated model for studying the simultaneous evolution of asteroid sizes and spin rates over solar system history. In order to understand collisional changes in spin rates in our model, we systematically explore a four-dimensional model parameter space with fixed initial size and spin distributions for the asteroids. We select low and high values of the four important parameters of the model, chosen to span the reasonable range of parameter space, and consider both strain-rate dependent and strain-rate independent scaling of impact strengths. Thirty-two collisional scenarios are generated and analyzed with regard to the change in the spin rate as a function of asteroid size. We conclude that: The spin evolution is strongly coupled to the size evolution. The observed relative spin-down of asteroids 100 km in diameter is likely to be the result of the angular momentum "splash" effect. Experimentally derived values of fragment spin parameters lead to predictions of faster than observed rotation rates for small asteroids. The spin rates of all asteroids except possibly the largest ones have been significantly altered by collisions over solar system history. In general, shattering impacts are much more important than cratering events in changing the spin of asteroids.
ASTEROID COLLISIONAL EVOLUTION - AN INTEGRATED MODEL FOR THE EVOLUTION OF ASTEROID ROTATION RATES
PAOLICCHI, PAOLO;
1992-01-01
Abstract
We combine experimental data and theoretical results to develop a model for the changes in the rotation rates of fragments produced by large collisions that break up and disperse asteroidal targets. Collisions that partially disperse the target can also produce a despinning of the reaccumulated core due to the angular momentum "splash" effect arising from the preferential escape of material with higher than average angular momentum (Cellino et al. 1990, Paper I). Combining these results with previously published work on spin rate changes for cratering impacts (Harris 1979; Dobrovolskis & Burns 1984), we present a comprehensive model for the changes in asteroid spin rates due to collisions. This spin change algorithm, when incorporated into an existing simulation of collisional effects on asteroid sizes, produces an integrated model for studying the simultaneous evolution of asteroid sizes and spin rates over solar system history. In order to understand collisional changes in spin rates in our model, we systematically explore a four-dimensional model parameter space with fixed initial size and spin distributions for the asteroids. We select low and high values of the four important parameters of the model, chosen to span the reasonable range of parameter space, and consider both strain-rate dependent and strain-rate independent scaling of impact strengths. Thirty-two collisional scenarios are generated and analyzed with regard to the change in the spin rate as a function of asteroid size. We conclude that: The spin evolution is strongly coupled to the size evolution. The observed relative spin-down of asteroids 100 km in diameter is likely to be the result of the angular momentum "splash" effect. Experimentally derived values of fragment spin parameters lead to predictions of faster than observed rotation rates for small asteroids. The spin rates of all asteroids except possibly the largest ones have been significantly altered by collisions over solar system history. In general, shattering impacts are much more important than cratering events in changing the spin of asteroids.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
