Presentation #523.07 in the session Observing and Modeling NEO Properties (iPosters).
The surface of rubble pile asteroids, i.e. celestial bodies consisting of gravitationally bound granular particles and with a size in the range of several hundred meters to few kilometers, appears to be inhomogeneously structured . The JAXA space mission Hayabusa found the asteroid 25143 Itokawa to show seas of small particles, clearly segregated from areas covered by bigger rocks. We investigate the hypothesis that this sorting happens due to different rebound efficiencies of particles impacting the asteroid depending on the target particle size. The basis of this reasoning, the so-called Ballistic Sorting Effect (BSE) , is the assumption of a growing coefficient of restitution for larger target particles, resulting in impactors to lose more energy on fine grained targets and aggregate in those areas.
Our approach to test this hypothesis is by recreating an asteroid surface as accurately as possible by having a surface of asteroid simulant in an environment of constant asteroid gravity under vacuum . On this surface we perform low velocity impacts and measure the coefficient of restitution. In addition, we perform numerical DEM simulations to back our experimental data. We find that the coefficient of restitution does not decline monotonically for arbitrarily small target surface particles but shows a minimum. With the aid of our simulation, we show this to be caused by cohesion. For sorting this means that the sorting efficiency is best for certain bed particle sizes or size ratios, when the cohesion is on the same order of magnitude as gravity.
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