Mercury's Hidden Past: Revealing a Volatile-dominated Layer through Glacier-like Features and Chaotic Terrains

The discovery of global elemental volatile compositions, sublimation hollows, and chaotic terrains has significantly reshaped our understanding of Mercury's geology. These findings suggest the existence of volatile-rich layers (VRLs) extending several kilometers in depth, challenging the traditionally held view of a predominantly volatile-devoid Mercury crust. However, the precise nature and origin of these VRLs remain to be elucidated. The Raditladi basin exhibits morphologies analogous to terrestrial and Martian glaciers. These geomorphological features are potentially derived from impact-exposed VRLs, likely constituted of halite, other semivolatile salts, or organic volatiles. The distinctive rheological traits of substances such as halite substantiate this hypothesis. The inference posits a potential ubiquity of VRLs on a planetary scale, albeit potentially ensconced at considerable depth in specific regions. North polar chaotic terrains elucidate the VRLs' genesis and temporal evolution. The intense fragmentation of heavily cratered landscapes during their formation indicates a composition dominated by volatiles. This finding postulates a phase of volatile-enriched crustal accretion predating the Late Heavy Bombardment (similar to 3.9 Ga). Regardless of lost mass, the unaltered basal elevation post-collapse signals a transition to a volatile-free stratum. The exposure of an exhumed lithological substrate within Mercury's stratigraphy, identifiable in gravimetry as an impacted paleosurface, contests the magma ocean differentiation concept for VRL formation. It infers a grand-scale construct originating from depositional processes, possibly due to the collapse of a transient, hot primordial atmosphere.