Effect of impact velocity and acoustic fluidization on the simple-to-complex transition of lunar craters

TL;DR

This study uses numerical modeling to explore how impact velocity and acoustic fluidization influence the transition from simple to complex lunar craters, highlighting the importance of impact conditions and fluidization parameters.

Contribution

It demonstrates that impact velocity and acoustic fluidization parameters critically affect crater morphology and supports scaling impactor size for modeling lunar crater transitions.

Findings

Transition is sensitive to fluidization decay and viscosity constants.

Impact velocity and size combination significantly influences crater morphology.

Scaling block size by impactor size aligns better with observed lunar craters.

Abstract

We use numerical modeling to investigate the combined effects of impact velocity and acoustic fluidization on lunar craters in the simple-to-complex transition regime. To investigate the full scope of the problem, we employed the two widely adopted Block-Model of acoustic fluidization scaling assumptions (scaling block size by impactor size and scaling by coupling parameter) and compared their outcomes. Impactor size and velocity were varied, such that large/slow and small/fast impactors would produce craters of the same diameter within a suite of simulations, ranging in diameter from 10-26 km, which straddles the simple-to-complex crater transition on Moon. Our study suggests that the transition from simple to complex structures is highly sensitive to the choice of the time decay and viscosity constants in the Block-Model of acoustic fluidization. Moreover, the combination of impactor size and velocity plays a greater role than previously thought in the morphology of craters in the simple-to-complex size range. We propose that scaling of block size by impactor size is an appropriate choice for modeling simple-to-complex craters on planetary surfaces, including both varying and constant impact velocities, as the modeling results are more consistent with the observed morphology of lunar craters. This scaling suggests that the simple-to-complex transition occurs at a larger crater size, if higher impact velocities are considered, and is consistent with the observation that the simple-to-complex transition occurs at larger sizes on Mercury than Mars.