Momentum Transfer in Oblique Impacts: Implications for Asteroid Rotations

Collisional Spin Up of Nonspherical Asteroids

“…However, m could differ between the two conditions because the ζ 's for the rocky and metallic asteroid models (Table I) were obtained with nylon projectiles. Yanagisawa and Hasegawa (2000) found that ζ depended on target material. Their result (Fig.…”

“…However, it must contribute importantly to the rotation of nonspherical bodies. Laboratory experiments show that the impulse is equivalent in magnitude to the projectile's pre-impact momentum in the collisions on brittle targets (Yanagisawa et al 1996, Yanagisawa and Hasegawa 1999, 2000. Thus, neglecting the impulse is not appropriate for nonspherical bodies.…”

“…The experiments show the clear dependence of the parameters on the incident angle of the projectile measured from the surface normal, θ. Yanagisawa and Hasegawa (2000) proposed simple mathematical expressions for the dependence as…”

“…Even if all the momentum is not transferred and the projectile's ricochet or vapor plume carries some away, a circular crater is formed in the excavation stage. The momenta of post-impact targets have been measured in many laboratory impact experiments (Davis and Weidenschilling 1982, Yanagisawa et al 1996, Yanagisawa and Hasegawa 2000. The results show that the impacts are not perfectly inelastic in the direction tangential to the target surface while circular craters are formed, except for very grazing impacts.…”

Role of target strength in momentum enhancement

“…decreasing target fracture stress while maintaining target flow stress (β increases with decreasing fracture stress); 2. decreasing target flow stress while maintaining target fracture stress (β increases with decreasing flow stress). To assess the first result, it seems intuitively obvious that more brittle materials will have larger momentum enhancements and the limited data on momentum enhancement into brittle materials such as ice or rock show that they have higher momentum enhancements than metals, though they are different materials [4]. However, the data with the two aluminum alloys did not agree with the computational results of #2 -the data clearly showed that the weaker material had a lower β.…”