Reshaping and ejection processes on rubble-pile asteroids from impacts

Abstract

Context. Most small asteroids (< 50 km in diameter) are the result of the breakup of a larger parent body and are often considered to be rubble-pile objects. Similar structures are expected for the secondaries of small asteroid binaries, including Dimorphos, the smaller component of the 65 803 Didymos binary system and the target of NASA’s Double Asteroid Redirection Test (DART) and ESA’s Hera mission. The DART impact will occur on September 26, 2022, and will alter the orbital period of Dimorphos around Didymos. Aims. In this work we assume Dimorphos-like bodies with a rubble-pile structure and quantify the effects of boulder packing in its interior on the post-impact morphology, degree of shape change, and material ejection processes. Methods. We used the Bern smoothed particle hydrodynamics shock physics code to numerically model hypervelocity impacts on small, 160 m in diameter, rubble-pile asteroids with a variety of boulder distributions. Results. We find that the post-impact target morphology is most sensitive to the mass fraction of boulders comprising the target, while the asteroid deflection efficiency depends on both the mass fraction of boulders on the target and on the boulder size distribution close to the impact point. Our results may also have important implications for the structure of small asteroids.

Global Mapping of Fragmented Rocks on the Moon with a Neural Network: Implications for the Failure Mode of Rocks on Airless Surfaces

“…Interpretation: morphology resulting from an impact into a fine-grained target (i.e., regolith) containing large inclusions (i.e., preexisting boulders or fractured bedrock) and different from that of an impact into a target composed of only fine-grained or large particles (e.g., Güttler et al 2012). The spatially inhomogeneous distribution of boulders around the impact site, i.e., the rays and the pattern, are consistent with laboratory and numerical simulations of impact into a target with a wide range of particle sizes without a dominant particle size (e.g., Kadono et al 2019Kadono et al , 2020Raducan et al 2022b;Ormö et al 2022). The observed radial pattern is itself the result of filament structure in the ejecta curtain (e.g., Kadono et al 2022).…”

Successful kinetic impact into an asteroid for planetary defence

“…There is no evidence for expansive smooth deposits (grain size smaller than the image pixel scale) such as those seen on Itokawa 17 . The blocky nature of the impact site probably influenced crater formation, ejecta and momentum enhancement, as seen in impact experiments 28 , 32 – 34 , numerical simulations 25 , 35 and the Small Carry-on Impactor experiment on Hayabusa2 5 .…”

The Dimorphos Boulder Swarm

“…This is about 0.1% of the 4 × 10 9 kg mass of Dimorphos and about 10 4 times the mass of the DART impactor. The ejected mass is comparable to models of impact into a dense-packed field of 7 m sized boulders (Panel (c) from Raducan et al 2022) and of the same order as the nominal 1.5×10 6 kg mass loss predicted by Fahnestock et al (2022). A slightly larger mass, 0.3% to 0.5% of the mass of Didymos, was inferred from the diffuse material (Graykowski et al 2023) while a wider range, 0.2% to 1.2%, was determined from submillimeter wavelength observations (Roth et al 2023).…”

“…and with laboratory experiments showing only a weak dependence of speed on size(Nakamura & Fujiwara 1991;Nakamura et al 1992;Raducan et al 2022). …”