Transmission of a Seismic Wave generated by impacts on Granular Asteroids

TL;DR

This study uses discrete element simulations to analyze seismic wave transmission and attenuation in granular asteroids, revealing high energy dissipation and impact-dependent wave speeds relevant for space missions and asteroid surface processes.

Contribution

It provides new insights into seismic wave behavior in granular asteroids, including wave speed dependence on pressure and impact velocity, with implications for interpreting surface phenomena.

Findings

Seismic wave speed can reach hundreds of m/s at low pressures.

Wave velocity depends on pressure as P^{1/6}.

Energy dissipation during wave transmission is extremely high.

Abstract

In this paper we use a Soft-Sphere Discrete Element method code to simulate the transmission and study the attenuation of a seismic wave. Then, we apply our findings to the different space missions that have had to touch the surface of different small bodies. Additionally, we do the same in regards to the seismic wave generated by the hypervelocity impacts produced by the DART and Hayabusa2 missions once the shock wave transforms into a seismic wave. We find that even at very low pressures, such as those present in the interior of asteroids, the seismic wave speed can still be on the order of hundreds of m/s depending on the velocity of the impact that produces the wave. As expected from experimental measurements, our results show that wave velocity is directly dependent on $P^{1/6}$, where $P$ is the total pressure (confining pressure plus wave induced pressure). Regardless of the pressure of the system and the velocity of the impact (in the investigated range), energy dissipation is extremely high. These results provide us with a way to anticipate the extent to which a seismic wave could have been capable of moving some small particles on the surface of a small body upon contact with a spacecraft. Additionally, this rapid energy dissipation would imply that even hypervelocity impacts should perturb only the external layer of a self-gravitating aggregate on which segregation and other phenomena could take place. This would in turn produce a layered structure of which some evidence has been observed