Laboratory Impact Splash Experiments to Simulate Asteroid Surfaces

TL;DR

This study uses laboratory impact experiments to simulate asteroid surface processes, revealing that impacts cause minimal ejecta and high energy dissipation, which influences surface evolution and grain distribution.

Contribution

It provides the first detailed laboratory characterization of impact ejecta and energy dissipation on granular beds simulating asteroid surfaces.

Findings

Impacts eject fewer than 10 particles, which rise less than one particle diameter.

Impacts significantly slow down the impactor, reducing its velocity to about 20%.

Impacts trap grains near the site, affecting surface morphology and grain size distribution.

Abstract

Granular material that is bound by the low gravity of a small asteroid is mobilized by slow velocity impacts. These splashes generated by impacts might play an important role in sculpting the asteroid's surface. In laboratory experiments we characterize the ejecta generated by spherical 150 $\rm \mu m$ diameter basalt grains impacting a granular bed at 0.8 m/s. We find that such an impact typically leads to less than 10 particles being ejected from the granular bed, with typical ejecta trajectories rising to less than one particle diameter above the surface. That is, the observed impacts are highly dissipative and only a small fraction of the impact energy is imparted onto the ejecta. While the impactor itself still rebounds, it typically slows down significantly to an average of about 20 % of its impact velocity. Scaled to asteroids, impactor and ejecta generated from impacts of sand sized grains are not able to spread over the asteroid's surface but will stay close to the impact site. Therefore these highly inelastic impacts into soft granular beds efficiently trap grains, in contrast to more elastic impacts on bare, rocky surfaces confirming suggestions by Shinbrot (2017). This is also in agreement to observed features on asteroids as this topological elasticity bias suggests that redistribution of grains leads to a size segregation.