Cratering Experiments on Granular Targets With a Variety of Particle Sizes: Implications for Craters on Rubble‐Pile Asteroids

Abstract

We performed cratering experiments on targets composed of glass beads with a power‐law size distribution that simulated the surface of rubble‐pile asteroids, and we improved the previously studied reduction factor on the crater size scaling relationship including the armoring effect using the momentum transfer efficiency. Cratering experiments were conducted using light gas guns at Kobe University and ISAS/JAXA to control the impact velocity, vi ${v}_{\mathrm{i}}$, from 50 to 4,400 m s−1. Two kinds of mixed targets were prepared by mixing glass beads with diameters of 0.1, 1, 3, and 10 mm—one with the smallest diameter beads, and one without. The size ratio of the target bead to the projectile (diameter of 1–3 mm), ϕ $\phi $, changed from 0.03 to 10. The crater size scaling relationships for the mixed targets were found to depend on the first contacted bead size. Notably, first contact with a 10 mm‐sized bead reduced the crater radius by 35% in maximum. The reduction factor due to this armoring effect on the crater size scaling relationship is written as follows: f(ϕ)=1+8.99×10−3vnormali0.630.34ϕ−0.19 $f(\phi )={\left[1+\left(8.99\times {10}^{-3}\right){v}_{\mathrm{i}}^{0.63}\right]}^{0.34}{\phi }^{-0.19}$; it decreased with the increase of the size ratio of the target bead to the projectile, while it increased with the increase of the impact velocity and approached unity. Our improved crater size scaling relationship that includes the reduction factor could be used to reconstruct the crater size frequency distribution on rubble‐pile asteroids such as Ryugu, and it may lead to a revision of the crater chronology of asteroids.

Recent results of stellar occultations by (60558) Echeclus

“…An assumed range of densities was used to investigate Echeclus interior properties to obtain meaningful results. The For a global density between 500 and 2,500 kg m −3 , a reasonable range of densities for Centaurs and TNOs (Sicardy et al 2011), Echeclus must have internal friction between 8.5 • > 𝜙 > 10.5 • (Figure 3), compatible with what is expected for a mixture of ice and rock (Barucci et al 2004;Yasui & Arakawa 2009). For comparison, Ortiz et al (2017) determined a friction angle for Haumea between 10 • and 15 • , considering the c/a = 0.4 ratio.…”

“…Hence, it is likely that Echeclus has a heterogeneous internal structure. Given its small size and the consequent unlikeliness that it had sufficient internal heat to experience any significant degree of differentiation (Shchuko et al 2014), it is possible that it has a heterogeneous distribution of mass, a rubble-pile structure or similar, with significant internal porosity may be as high as 20-30% in total volume (Yasui & Arakawa 2009).…”

The Relative Effects of Surface and Subsurface Morphology on the Deflection Efficiency of Kinetic Impactors: Implications for the DART Mission

“…However, we note that a 3D validation study is ongoing for iSALE (Ormö et al 2023). Future work may investigate code validation against experimental data, like recent laboratory impact experiments conducted on targets consisting of various sizes of boulders (Barnouin et al 2019;Kadono et al 2020;Okawa et al 2022;Yasui et al 2022). iSALE-2D simulations were performed where the projectile was modeled as three 63% porous aluminum spheres aligned in series impacting a rubble-pile target with an assembly of multiple boulders at the impact site embedded in a matrix material (Figure A1).…”