Subsurface stratigraphy suggested by the layered ejecta craters in the Martian northern planitiae

Abstract

The formation of layered ejecta craters (LECs) is generally thought to be related to the subsurface water-ice. The distribution of LECs in the northern regions of Mars (0 to 70° N) features both local and latitudinal variations, e.g., there are generally few LECs within volcanic areas, and the observed minimum and median diameters of the LECs decreases with increasing latitude. The observed minimum diameters of the LECs in the six planitiae within the northern lowlands suggest the roof depth of the LECs-forming layer has clear lateral variability, ranging between ∼90 m in the Arcadia Planitia and ∼280 m in the Isidis Planitia. The observed LECs are suggested to mainly form during the Amazonian, implying that the LEC-forming water-ice-bearing strata might be still present. The variation might reflect the comprehensive influence on the subsurface water-ice by the climate conditions and geologic events during the Amazonian period. The proposed subsurface stratigraphies in the six planitiae suggest that the total thickness of the LECs-related strata in the Chryse Planitia is the largest (∼4.6 km) and in the Arcadia Planitia is the smallest (∼1.6 km). There could be as much as ∼3.5–16 million km3 subsurface water stored in these strata, resulting in a ∼24–110 m global equivalent layer (GEL) of water. Given that water is a fundamental ingredient to life, its migration from surface to subsurface shifts the focus of its exploration. Both Arcadia and Utopia Planitiae represent ideal candidates as locations where both shallow and deep subsurface water-ice might be abundant, they represent high-priority targets for future missions at mid-latitudes for biosignature searching and in-situ resource utilization.