Numerical Simulations of the Apollo S‐IVB Artificial Impacts on the Moon

A Rajšić,K Miljković,G S Collins,K Onodera,T Kawamura,N Wójcicka,P Lognonné,M A Wieczorek,I J Daubar

doi:10.1029/2021ea001887

Abstract

AbstractThe third stage of the Saturn IV rocket used in the five Apollo missions made craters on the Moon ∼30 m in diameter. Their initial impact conditions were known, so they can be considered controlled impacts. Here, we used the iSALE‐2D shock physics code to numerically simulate the formation of these craters, and to calculate the vertical component of seismic moment (∼4 × 1010 Nm) and seismic efficiency (∼10−6) associated with these impacts. The irregular booster shape likely caused the irregular crater morphology observed. To investigate this, we modeled six projectile geometries, with footprint area between 3 and 105 m2, keeping the mass and velocity of the impactor constant. We showed that the crater depth and diameter decreased as the footprint area increased. The central mound observed in lunar impact sites could be a result of layering of the target and/or low density of the projectile. Understanding seismic signatures from impact events is important for planetary seismology. Calculating seismic parameters and validating them against controlled experiments in a planetary setting will help us understand the seismic data received, not only from the Moon, but also from the InSight Mission on Mars and future seismic missions.

Highlights

The NASA InSight Mission has been recording seismic activity on the surface of Mars since late 2018 (e.g., Banerdt et al, 2020)
This work connected numerical impact simulations with seismic parameters related to the Apollo Saturn IV boosters (S-IVB) artificial impacts on the Moon that were recorded by the lunar seismic network
After confirming that our simulations are approximately consistent with observed crater dimensions, further simulations were performed to investigate the generation of the seismic source and calculate seismic properties associated with the impact event

Summary

Introduction

The NASA InSight Mission has been recording seismic activity on the surface of Mars since late 2018 (e.g., Banerdt et al, 2020). To date none of these signals have been unambiguously associated with an impact event (Daubar et al, 2020). This calls for further investigation of meteorite strikes and the relationship between impact parameters and the amplitude of the seismic signals they generate. The artificial craters that were made by the Saturn IV boosters (S-IVB) impacting the Moon (Wagner et al, 2017) represent large scale impact experiments (Figure 1). They provide a valuable link between known impact conditions and resulting crater size. The seismic signals generated by these impacts were recorded by the Apollo seismic network operating on the Moon at the time, which provided information about impact-induced seismicity on the Moon (e.g., Gudkova et al, 2015; Latham et al, 1970; Lognonné, 2005; Lognonné & Mosser, 1993; Lognonné et al, 2009; Onodera et al, 2021; Toksöz et al, 1974)

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