Collisional disruption of ice by high-velocity impact

M. Arakawa, Collisional disruption of ice by high-velocity impact, ICARUS, 142(1), 1999, pp. 34-45
Citations number
Categorie Soggetti
Space Sciences
Journal title
ISSN journal
0019-1035 → ACNP
Year of publication
34 - 45
SICI code
High-velocity impact among icy planetesimals is a physical phenomenon impor tant to the planetary evolution process in the outer Solar System. In order to study this phenomenon, impact experiments on water ice were made by usi ng a two-stage light gas gun installed in a cold room(-10 degrees C) to cla rify the elementary processes of collisional disruption and to study the re accumulation and the escape conditions of the impact fragments. Cubic ice t argets ranging in size from 15 to 100 mm were impacted by a nylon projectil e of 7 mg with an impact velocity (v(i)) from 2.3 to 4.7 km/s. The correspo nding mass ratio of the projectile to the target (m(p)/M-t) ranged from 10( -3) to 10(-6), which is two orders of magnitude lower than that used in pre vious studies (Arakawa et al. 1995, Icarus 118, 341-354). As a result, we o btained data on elementary processes such as attenuation of the shock wave and fragmentation dynamics. We found that the shock pressure attenuates in the ice target according to the relation of P proportional to (L-p/r)(2), i rrespective of the mass ratio between 10(-3) and 10(-5), where L-p is the p rojectile size and r is a propagation distance. The largest fragment mass ( m(l)) normalized by the original target mass has a good relationship to a n ondimensional impact stress (P-I, NDIS) defined as the ratio of the antipod al pressure to the material strength. This relationship is described as m(l )/M(t)proportional to P-I(-1.7) for a wide range of impact conditions (50 m /s < v(i) < 4 km/s and 10(-1) < m(l)/M-t, < 10(-6)), and shows the utility of NDIS. Using a measured shock wave decay constant of 2, the reaccumulatio n and the escape conditions of icy bodies in high-velocity collisions were estimated. As a result, it was clarified that a rubble pile could be formed when large icy bodies (radius > 20 km) reaccumulated. On the other hand, w hen smaller icy bodies (radius < 2 km) disrupted catastrophically, all frag ments escaped and a rubble pile was never formed. (C) 1999 Academic Press.