Crustal Structural Layering and Regional Stratigraphic Variations on Mars

The layered architecture of the Martian crust, a central theme in exploration, holds crucial clues to the planet’s geological evolution and environmental history. Our current understanding of this layered structure and its properties stem primarily from in situ geophysical experiments—seismic investigations by NASA’s InSight mission and ground-penetrating radar (GPR) surveys by the Perseverance (NASA) and Zhurong (CNSA) rovers. Seismic data from InSight indicate that the crust at the landing site is approximately 40 km thick, with prominent velocity discontinuities at depths of around 10 km and 20 km, dividing it into distinct upper, middle, and lower layers. The upper crust exhibits finer-scale stratification, including detectable interfaces at about 2 km, 750 m, and within the top 100 m. These features likely record a complex history of alternating magmatic and sedimentary resurfacing processes in the region. At shallower depths, GPR observations highlight pronounced regional variability. In a landmark achievement, the Zhurong rover’s dual-frequency GPR has revealed multiscale layering—from centimeters to tens of meters—within the top 80 m. The smooth gradient in physical properties, together with the dielectric permittivity and attenuation characteristics of these strata, suggests prolonged yet episodic water-assisted sedimentation in the Zhurong landing area from about 3.5–3.2 Ga until as recently as a few hundred million years ago. In contrast, subsurface profiles at other sites bear a stronger signature of magmatic activity: Perseverance’s GPR detected coherent reflective interfaces within the top ~15 m, while a similar shallow structure is observed within the top 100 m at the InSight landing site. These contrasts underscore substantial regional heterogeneity in Martian stratigraphy and geological evolution. Marsquake relocation studies further indicate spatially variable tectonic activity across different regions of present-day Mars. Despite these advances, fundamental questions remain regarding the lateral variability of crustal structure, the relationship between layering and water distribution, deep interior (mantle and core) stratification, and the origin of the hemispheric dichotomy. Addressing these issues will help prioritize objectives for future Mars exploration.