Rethinking the stratigraphy of the Moon’s regolith: A glimpse from Chang’E-3 Lunar Penetrating Radar

Most previous studies about near surface structure of the Moon utilized a two-layer scenario, i.e., a fine-grained regolith layer and the underlying bedrock. On 14 December, China’s Chang’E-3 spacecraft successfully landing on the east rim of a young crater (CE-3 crater) in Mare Imbrium. The lunar penetrating radar observations reveal four major stratigraphic zones from the surface to a depth of ~20 m: a layered reworked zone, an ejecta layer, a paleoregolith layer, and the underlying mare basalts. The reworked zone has two to five distinct layers and consists of newly formed regolith since the formation of the CE-3 crater. Thickness of the paleoregolith is about 4-11 m, which is consistent with the regolith thickness of the background geologic unit estimated from morphologies of small impact craters. Since CE-3 crater is very young, thickness of the reworked zone indicates a rapid regolith growth rate than previous thought. The four-layer stratigraphic structure at the landing site mainly results from the formation of the CE-3 crater and later surface modification. Preliminary analysis of the degradation of small craters over two other geologic units indicates that structure at the CE-3 landing site might be common, consisting more than 40% of the lunar surface. If this is true, then the two-layer scenario regolith stratigraphy should be revised for future study.