Impact flash evolution of CO2 ice, water ice, and frozen Martian and lunar regolith simulant targets

Jon D Tandy,Mike J Cole,Mark C Price,Luke S Alesbrook,Penny J Wozniakiewicz,Chrysa Avdellidou

doi:10.1111/maps.13581

Abstract

AbstractThe wavelength dependence and temporal evolution of the hypervelocity impact self‐luminous plume (or “flash”) from CO2 ice, water ice, and frozen Martian and lunar regolith simulant targets have been investigated using the Kent two‐stage light‐gas gun. An array of 10 band‐pass filtered photodiodes and a digital camera monitored changes in the impact flash intensity during the different phases of the emitting ejecta. Early‐time emission spectra were also recorded to examine short‐lived chemical species within the ejecta. Analyses of the impact flash from the varied frozen targets show considerable differences in temporal behavior, with a strong wavelength dependence observed within monitored near‐UV to near‐IR spectral regions. Emission spectra showed molecular bands across the full spectral range observed, primarily due to AlO from the projectile, and with little or no contribution from vaporized metal oxides originating from frozen regolith simulant targets. Additional features within the impact flash decay profiles and emission spectra indicate an inhomogeneity in the impact ejecta composition. A strong correlation between the density of water ice‐containing targets and the impact flash rate of decay was shown for profiles uninfluenced by significant atomic/molecular emission, although the applicability to other target materials is currently unknown. Changes in impact speed resulted in considerable differences in the temporal evolution of the impact flash, with additional variations observed between recorded spectral regions. A strong correlation between the impact speed and the emission decay rate was also shown for CO2 ice targets. These results may have important implications for future analyses of impact flashes both on the lunar/Martian surface and on other frozen bodies within the solar system.

Highlights

Intense, short-lived light flashes are produced during hypervelocity impacts; flashes resulting from high-speed lunar impacts are so energetic that they are frequently observed by modest facilities (Dunham et al, 2000; Cudnik et al, 2003; Suggs et al, 2014; Avdellidou & Vaubaillon, 2019)
This study investigates the wavelength dependence and temporal evolution of hypervelocity impact flashes from CO2 ice, water ice and frozen Martian and lunar regolith-simulant targets
This study illustrates the considerable benefits of spectroscopically examining impact ejecta, which show a strong and varied wavelength dependence upon several impact parameters, with atomic/molecular emission influencing the temporal evolution of the ejecta flash

Summary

Introduction

Short-lived light flashes are produced during hypervelocity impacts; flashes resulting from high-speed lunar impacts are so energetic that they are frequently observed by modest facilities (Dunham et al, 2000; Cudnik et al, 2003; Suggs et al, 2014; Avdellidou & Vaubaillon, 2019). The temporal evolution of impact flashes are typically monitored in the laboratory using photodetectors (Eichhorn, 1976; Burchell et al, 1996; Ernst & Schultz, 2003, 2004, 2007; Bergeron et al, 2006; Lawrence et al, 2006; Tsembelis et al, 2008; Ernst et al, 2011; Goel et al, 2015; Yafei et al, 2019) or high-speed cameras (Kondo & Ahrens, 1983; Schultz, 1996; Ernst & Schultz, 2007; Schultz et al, 2007; Mihaly et al, 2013, 2015; Tandy et al, 2014; Schultz & Eberhardy, 2015), revealing multiple phases of the radiating impact ejecta. The temporal changes in the emission and the transient chemical species generated from these frozen targets warrant further investigation

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Conclusion