Content area
Full Text
letters to nature
typically slower than [H11011]1kms1) might differ signicantly from what is assumed by current modelling efforts27. The expected
equation-of-state differences among small bodies (ice versus rock, for instance) presents another dimension of study; having recently adapted our code for massively parallel architectures (K. M. Olson and E.A, manuscript in preparation), we are now ready to perform a more comprehensive analysis.
The exploratory simulations presented here suggest that when a young, non-porous asteroid (if such exist) suffers extensive impact damage, the resulting fracture pattern largely denes the asteroids response to future impacts. The stochastic nature of collisions implies that small asteroid interiors may be as diverse as their shapes and spin states. Detailed numerical simulations of impacts, using accurate shape models and rheologies, could shed light on how asteroid collisional response depends on internal conguration and shape, and hence on how planetesimals evolve. Detailed simulations are also required before one can predict the quantitative effects of nuclear explosions on Earth-crossing comets and asteroids, either for hazard mitigation28 through disruption and deection, or for resource exploitation29. Such predictions would require detailed reconnaissance concerning the composition and internal structure of the targeted object. [H18554]
Collective dynamics of small-world networks
Duncan J. Watts* & Steven H. Strogatz Department of Theoretical and Applied Mechanics, Kimball Hall, Cornell University, Ithaca, New York 14853, USA
8
.........................................................................................................................
Received 4 February; accepted 18 March 1998.
1. Asphaug, E. & Melosh, H. J. The Stickney impact of Phobos: A dynamical model. Icarus 101, 144164 (1993).
2. Asphaug, E. et al. Mechanical and geological effects of impact cratering on Ida. Icarus 120, 158184 (1996).
3. Nolan, M. C., Asphaug, E., Melosh, H. J. & Greenberg, R. Impact craters on asteroids: Does strength or gravity control their size? Icarus 124, 359371 (1996).
4. Love, S. J. & Ahrens, T. J. Catastrophic impacts on gravity dominated asteroids. Icarus 124, 141155 (1996).
5. Melosh, H. J. & Ryan, E. V. Asteroids: Shattered but not dispersed. Icarus 129, 562564 (1997).6. Housen, K. R., Schmidt, R. M. & Holsapple, K. A. Crater ejecta scaling laws: Fundamental forms based on dimensional analysis. J. Geophys. Res. 88, 24852499 (1983).
7. Holsapple, K. A. & Schmidt, R. M. Point source solutions and coupling parameters in cratering mechanics. J. Geophys. Res. 92,...