Mass-velocity distributions of fragments in oblique impact cratering on gypsum

Abstract

Oblique impact cratering experiments into gypsum targets were performed, and masses and velocities of the fragments were measured within the observational limit of 0.1-100 m/s in velocity and 0.0003-1 g in mass. The fragments observed were divided in two groups according to ejection time: early fragments ejected conically within a few msec after the impact followed by late fragments consisting of hundreds of slow, small fragments ejected almost perpendicular to the target. The relationship between mass and velocity of early fragments was observed to follow a power law with an exponent of -0.11 +/- 0.06, consistent with previous studies (e.g., Nakamura and Fujiwara 1991; Giblin et al. 1998). The cumulative number of fragments heavier or equal to a given mass versus fragment mass distributions shows a power law exponent of -1.49 +/- 0.09 for late fragments and steeper than -0.49 +/- 0.18 for early fragments. More than 10% of the mass was ejected from the crater with ejection speed slower than 2 m/s. Those fragments will reaccumulate on porous (<1500 kg/m^3) and small (<4 km in diameter) asteroids.