We find evidence that crater ejecta play an important role in the small crater populations on the Saturnian satellites, and more broadly, on cratered surfaces throughout the Solar System. We measure crater populations in Cassini images of Enceladus, Rhea, and Mimas, focusing on image data with scales less than 500 m/pixel. We use recent updates to crater scaling laws and their constants to estimate the amount of mass ejected in three different velocity ranges: (i) greater than escape velocity, (ii) less than escape velocity and faster than the minimum velocity required to make a secondary crater (v_min), and (iii) velocities less than v_min. Although the vast majority of mass on each satellite is ejected at speeds less than v_min, our calculations demonstrate that the differences in mass available in the other two categories should lead to observable differences in the small crater populations; the predictions are borne out by the measurements we have made to date. Rhea, Tethys, and Dione have sufficient surface gravities to retain ejecta moving fast enough to make secondary crater populations. The smaller satellites, such as Enceladus but especially Mimas, are expected to have little or no traditional secondary populations because their escape velocities are near the threshold velocity necessary to make a secondary crater. Our work clarifies why the Galilean satellites have extensive secondary crater populations relative to the Saturnian satellites. The presence, extent, and sizes of sesquinary craters (craters formed by ejecta that escape into temporary orbits around Saturn before re-impacting the surface) is not yet well understood. Finally, our work provides further evidence for a "shallow" size-frequency distribution (slope index of ~2 for a differential power-law) for comets a few km diameter and smaller. [slightly abbreviated]
Origin of asteroid (469219) Kamo`oalewa: the main asteroid belt or the Giordano Bruno crater on the Moon?
ESA ESRIN / PDO / NEO Coordination Centre（欧洲空间局地球观测站近地天体协调中心）；Deimos Italia s.r.l.（德伊莫斯意大利有限公司）；Department of Astronomy, Faculty of Mathematics, University of Belgrade（贝尔格莱德大学数学学院天文学系）；Centro de Estudios de Física del Cosmos de Aragón (CEFCA)（阿拉贡宇宙物理研究中心）；Department of Physics, University of Helsinki（赫尔辛基大学物理系）；Asteroid Engineering Laboratory, Luleå University of Technology（鲁勒理工大学小行星工程实验室）；Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences（中国科学院地球化学研究所地外行星科学中心）
Impact Ejecta near the Impact Point Observed using Ultra-high-speed Imaging and SPH Simulations, and a Comparison of the Two Methods
预计与撞击速度相当的高速撞击喷出物将有助于行星体之间的物质运输和喷出物远离撞击坑的沉积。我们研究了高速喷出物的行为产生的角度为45和90度，使用实验和数值方法。千叶工业大学行星探索研究中心（日本）开发的实验系统使我们能够观察喷出物的初始生长。我们成功地成像高速喷出物在0.2 $\mathrm{μ}$ s的时间间隔为4.8 mm直径的聚碳酸酯弹丸到聚碳酸酯板上的影响，在约4 km s $^{-1}$的冲击速度。光滑粒子流体动力学（SPH）模拟的各种数值分辨率进行了相同的影响条件有关的实验。我们比较了实验和模拟的喷出物的形态和速度，我们证实了高分辨率模拟的密切匹配（$\geq10^6$ SPH粒子代表抛射体）。根据高分辨率模拟得到的喷出物速度分布，斜撞击的高速喷出物的喷出速度远大于垂直撞击的喷出速度。在斜撞击中，平行于目标表面的穿透射弹的平移运动可能在喷出物的根部造成长期、持续的加速。
Tracking low-velocity ejecta from the DART impact on Dimorphos
Centro de Astrobiologia CSIC-INTA（西班牙国家航空航天技术研究所天体生物学中心）；Universidad Carlos III de Madrid（马德里卡洛斯三世大学）；Université Paris Cité, Institut de Physique du Globe de Paris, CNRS（巴黎西岱大学，巴黎地球物理研究所，法国国家科学研究中心）
