Numerous small bodies inevitably lead to cratering impacts on large planetary bodies during planet formation and evolution. As a consequence of these small impacts, a fraction of the target material escapes from the gravity of the large body, and a fraction of the impactor material accretes onto the target surface, depending on the impact velocities and angles. Here, we study the mass of the high-speed ejecta that escapes from the target gravity by cratering impacts when material strength is neglected. We perform a large number of cratering impact simulations onto a planar rocky target using the smoothed particle hydrodynamics method. We show that the escape mass of the target material obtained from our numerical simulations agrees with the prediction of a scaling law under a point-source assumption when $v_{\rm imp} \gtrsim 12 v_{\rm esc}$, where $v_{\rm imp}$ is the impact velocity and $v_{\rm esc}$ is the escape velocity of the target. However, we find that the point-source scaling law overestimates the escape mass up to a factor of $\sim 70$, depending on the impact angle, when $v_{\rm imp} \lesssim 12 v_{\rm esc}$. Using data obtained from numerical simulations, we derive a new scaling law for the escape mass of the target material for $v_{\rm imp} \lesssim 12 v_{\rm esc}$. We also derive a scaling law that predicts the accretion mass of the impactor material onto the target surface upon cratering impacts by numerically evaluating the escape mass of the impactor material. Our newly derived scaling laws are useful for predicting the escape mass of the target material and the accretion mass of the impactor material for a variety of cratering impacts that would occur on large planetary bodies during planet formation.
Lunar ejecta as the missing piece to resolve the lunar cratering asymmetry
State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology（澳门科技大学月球与行星科学国家重点实验室）；School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；Key Laboratory of Modern Astronomy and Astrophysics in Ministry of Education, Nanjing University（南京大学现代天文学与天体物理教育部重点实验室）
Impacts of thrusting, extensional faulting, and glaciation on cratering records of Pluto's largest moon Charon: Implications for the evolution of Kuiper belt objects
Dynamical evolution and surface accretion of DART impact ejecta in the (65803) Didymos system
University of Liverpool（利物浦大学）；Politecnico di Milano（米兰理工大学）；IFAC-CNR（意大利国家研究委员会应用研究所）；Universidad de Alicante（阿利坎特大学）；European Space Agency (ESA)（欧洲空间局）
The Physics of Protoplanetesimal Dust Agglomerates. X. Mechanical properties of dust aggregates probed by a solid-projectile impact
尘埃聚集体力学性质的动力学表征一直是定量讨论原行星盘中尘埃生长的重要问题之一。实验研究了固体弹丸低速（$\lesssim 3.2$ m s $^{-1}$）撞击下粉尘聚集体的动力学特性。在真空条件下，将由玻璃、钢或铅制成的球形冲击器落在填充部分$ϕ=0.35$的粉尘聚集体上。撞击导致尘埃聚集体的成坑或碎裂，这取决于撞击能量。陨石坑的形状可以近似为球形，没有观察到喷出物。为了了解撞击尘埃聚集体的基本物理学，固体抛射体的运动由高速相机获得。利用获得的撞击器位置数据，分析了撞击产生的阻力规律和动压。我们发现，有两个特征优势。一个是由撞击能量和凹坑体积之间的比率定义的，并且是$\simeq 120$ kPa。另一个强度指示动态压力的碎裂阈值，并且是$\simeq 10$ kPa。前者表征了明显的塑性形变，并且与负责撞击器减速的拖曳力一致。后者对应于产生裂纹的动态拉伸强度。利用这些结果，提出了一个简单的模型的压实和破碎的粉尘聚集体的阈值。此外，还比较了粉尘团聚体和松散颗粒物质的拖曳力规律，揭示了两种物质的异同。
