The role of target strength on the ejection of martian meteorites

Shock-recovered maskelynite indicates low-pressure ejection of shergottites from Mars

“…( 7 ) extracted pressure and velocity histories of multiple tracers in hydrocode spallation simulations and demonstrated that ejection from depth 1 to 2% of the impactor radius is most probable for achieving escape with a plateau-like P - t profile. Although their modeled impactor of 10-km radius corresponds to a very large crater, the same scaled depth in the case of a smaller impactor would still be consistent with the absolute depth needed to explain the differences noted between martian meteorites and surficial lithologies ( 48 ) and with the absence of 2π irradiation ( 49 ). By contrast, in previous scenarios requiring multistage P - t histories, ejecta likely originate at a depth of <0.5% of the impactor radius.…”

“…One remaining issue here is that peak pressure may still increase to >30 GPa in material ejected from greater depth but laterally close to the impact center. Elliot et al (48) applied a fragmentation model in their simulations and found that a 20-m layer of tuff on top of basalt enhances the overall ejection capability of a 1-km impactor, compared to pure basalt targets, potentially launching material from depth to escape at a lower peak pressure. In summary, somewhat counterintuitively, a decrease in the estimate of peak pressure recorded by the shergottites implies an increase in diameter of the crater from which they were ejected.…”

Constraining the formation and transport of lunar impact glasses using the ages and chemical compositions of Chang’e-5 glass beads

“…The likely explanation is that the estimated excavation depth for a crater of this size is 15 m (table S3), which provides a subequal sampling of the two layers (regolith and bedrock) for the assumed regolith thickness of 7 m. This indicates that the regolith composition and local structure can have substantial influence on ejecta behavior, and the set of model parameters explored here may not capture the full range of conditions in lunar impacts. Target and impact conditions (impact angle, size, and speed) would have a moderate effect on the ejection process ( 38 , 39 ); therefore, here, we limit the investigation to a combination of impact and target variations suitable for lunar regolith and small impacts on the Moon. Consequently, these models provide a baseline scenario in which the volume of melt produced in each crater and landing distance of ejecta would be the main factors that define the probability of glass from individual impact craters occurring in the Chang’e-5 soil sample ( Fig.…”

“…Glasses produced by impacts can be distinguished from those formed by volcanic eruptions using chemical and textural characteristics (1)(2)(3)(4). Previous studies of the 39 Ar- 40 Ar and U-Pb chronometric systems in lunar regolith glasses provide a foundation for investigating the volcanic and impact history of the Moon (3,(5)(6)(7)(8)(9)(10)(11)(12)(13). Volcanic glasses provide unique information about the lunar mantle (14,15), whereas impact glasses reflect the compositions of crustal target materials (16)(17)(18) and collisional dynamics of the inner solar system (4,9,19,20).…”