Contemporaneous formation of self-secondaries and layered ejecta deposits on Mars

Self-secondaries are secondary craters formed in cogenetic ejecta deposits. Bearing important information on cratering mechanics and the applicability of remote age-determination technique using crater statistics, the spatial distribution of self-secondaries on Mars and their potential effect on martian crater chronology remain uncharacterized. Here, we show that self-secondaries are scarce on Mars, possessing minor effect on crater chronology. Recognized self-secondaries primarily occur on rim deposits and are largely absent on layered ejecta deposits, suggesting that the emplacement of self-secondaries and layered ejecta deposits occurred in a narrow time window. Comparison with model-predicted distributions of self-secondaries suggests that fragments forming self-secondaries did not uniformly have near-vertical ejection angles and may have slightly larger angles than those of normal excavation flows, explaining their common occurrence on airless planetary bodies. The double-layered ejecta of Steinheim ceased emplacement earlier than single- and multiple-layered ejecta, possibly due to the higher volatile content in pre-impact target materials. Self-secondary impact craters are rare on Mars relative to airless bodies and are almost absent in layered ejecta deposits, according to satellite observations of Martian surface geology which suggest the two deposit types form largely contemporaneously.