arXiv 2008.087202020-08-20astro-ph.EPastro-ph.IM

在小行星级重力条件下的风化层特性：低速撞击毫米和厘米级颗粒目标

Regolith behavior under asteroid-level gravity conditions: Low-velocity impacts into mm- and cm-sized grain targets

J. Brisset, C. Cox, S. Anderson, J. Hatchitt, A. Madison, M. Mendonca, A. Partida, D. Remie

DOI：: 10.1051/0004-6361/202038665

摘要：

对小型小行星的现场观测表明，这类天体的表面经常被巨石和粗糙地形覆盖。风化层粒度分布在大约毫米和厘米尺度上，这种大颗粒在小天体表面的极低重力环境中的行为决定了它们的形态和演化。为了支持对自然过程的理解（例如，撞击喷出物的重新捕获）或航天器引起的相互作用（例如，一个小着陆器的命运），我们的目标是实验研究粗粒度的目标表面非常低速的影响（低于2米/秒）的反应。我们提出了一个厘米大小的球形弹丸到床的模拟风化层，由不规则的毫米和厘米大小的颗粒的86低速影响的结果。这些撞击是在真空和微重力条件下进行的。我们的研究结果包括测量的弹丸恢复恢复系数和穿透深度，以及喷出物的生产，速度和质量估计。我们发现，影响的结果包括经常发生的反弹和切向滚动的弹丸在目标表面上的影响。对于高于约12 cm/s的冲击速度产生喷出物，并且喷出物速度与射弹成比例以瞄准粒度比和冲击速度。喷出物的质量估计表明，喷出物越来越难以产生越来越大的颗粒尺寸。回弹射弹的恢复系数不显示对目标颗粒尺寸的依赖性，不像它们的最大穿透深度，其可以与射弹与目标颗粒尺寸比成比例。最后，我们将我们的实验测量结果与隼鸟2号的MASCOT着陆在小行星Ryugu表面上的航天器数据和数值工作进行了比较。

英文摘要：

In situ observations of small asteroids show that surfaces covered by boulders and coarse terrain are frequent on such bodies. Regolith grain sizes have distributions on approximately mm and cm scales, and the behavior of such large grains in the very low-gravity environments of small body surfaces dictates their morphology and evolution. In order to support the understanding of natural processes (e.g., the recapturing of impact ejecta) or spacecraft-induced interactions (e.g., the fate of a small lander), we aim to experimentally investigate the response of coarse-grained target surfaces to very-low-speed impacts (below 2 m/s). We present the outcome of 86 low-speed impacts of a cm-sized spherical projectile into a bed of simulated regolith, composed of irregular mm- and cm-sized grains. These impacts were performed under vacuum and microgravity conditions. Our results include measurements for the projectile coefficient of restitution and penetration depth, as well as ejecta production, speed, and mass estimation. We find that impact outcomes include the frequent occurrence of projectile bouncing and tangential rolling on the target surface upon impact. Ejecta is produced for impact speeds higher than about 12 cm/s, and ejecta speeds scale with the projectile to target the grain size ratio and the impact speed. Ejected mass estimations indicate that ejecta is increasingly difficult to produce for increasing grain sizes. Coefficients of restitution of rebounding projectiles do not display a dependency on the target grain size, unlike their maximum penetration depth, which can be scaled with the projectile to target grain size ratio. Finally, we compare our experimental measurements to spacecraft data and numerical work on Hayabusa 2's MASCOT landing on the surface of the asteroid Ryugu.

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