Effects of Moon's Thermal State on the Impact Basin Ejecta Distribution

Abstract

We investigate how different temperature gradients of the Moon affect the ejection of lithic and molten materials for impact basin several hundred kilometers in diameter to quantify the thickness and melt content of ejecta blanket as a function of radial distance. We find, by means of numerical modeling, that the ejecta thickness and melt content, similar to the basin formation, is sensitive to the thermal properties of the target. For two similar impact scenarios, the ejecta thickness with radial distance is proportional to a power law, but for a “warm” target, it declines faster than for a “cold” target. In addition, the impact on the warm target produces more molten ejecta than in the case of the cold target. The thermal effects on the ejecta thickness distribution can be testified by the topographic variations around Imbrium and Orientale basins, which were thought to be formed on a warm and cold Moon, respectively. Our study demonstrates that the thermal effect needs to be taken into account to estimate the ejecta thickness distribution for large‐scale impact basins on airless planetary surfaces.

Effect of target properties and impact velocity on ejection dynamics and ejecta deposition

“…Also in large‐scale cratering processes, iSALE is capable of producing ejection data that agrees with observable constraints as shown for the Orientale basin on the Moon, where the simulated ejecta deposit (for different lunar thermal conditions) was compared with LOLA observations (Zhu et al. , ).…”

“…Detailed comparison between model outputs and NASA Ames experimental data for impacts into quartz sand from the 1970s have shown that the iSALE shock physics code can accurately simulate the ejection process (W€ unnemann et al 2016). Also in large-scale cratering processes, iSALE is capable of producing ejection data that agrees with observable constraints as shown for the Orientale basin on the Moon, where the simulated ejecta deposit (for different lunar thermal conditions) was compared with LOLA observations (Zhu et al 2015(Zhu et al , 2017.…”

“…Zhu et al. ). However, further laboratory and modeling studies on this topic are needed to test this hypothesis including varying thermal profiles and using more complex rheological target setups.…”

Topographic Evolution of Von Kármán Crater Revealed by the Lunar Rover Yutu‐2

“…We assumed a vertical impact with a typical impact velocity of 15 km/s (Le Feuvre & Wieczorek, ) on a gabbroic target (Hurwitz & Kring, ; Potter et al, ). We tracked the ejecta trajectories during the impact cratering process and estimated the ejecta thickness at any given distance from the impact site (see Wünnemann et al, ; Zhu et al, , , ).…”

“…The three 360°image mosaics (left is north, clockwise) produced from the Pancam's left-eye images taken at the locations marked as black dots in Figure 2 labeled by S1, S2, and S3. tracked the ejecta trajectories during the impact cratering process and estimated the ejecta thickness at any given distance from the impact site (see Wünnemann et al, 2016;Zhu et al, 2015Zhu et al, , 2017Zhu et al, , 2019.…”