Impact-induced melting of materials with sparse thermodynamic data: The case of native sulfur on Mars

Sulfur is abundant on Mars and oxidized, resulting from massive early volcanism and aqueous activity as recorded by extensive sulfate-bearing terrains. Yet, a recent observation by NASA’s Curiosity rover indicates native sulfur is also preserved in the geological record and questions sources and mechanisms required to form such a deposit. A breached circular depression located within the light-toned Yardang unit upstream of the native sulfur deposit was proposed as a possible source. In this context, we test the possibility that a meteoritic impact on a sulfur-rich substrate can generate enough molten sulfur to account for the deposit. Given molten sulfur is expected to segregate from silicates, this process should lead to the formation of pure native sulfur accumulations. Here, we use the iSALE shock-physics code to estimate the amount of liquid sulfur segregating from the shocked material following vertical asteroid impacts on a sulfur-rich basaltic target. The impact parameters (mass, velocity) were varied and adjusted to match the diameter of the circular depression observed within the light-toned Yardang unit ( 390 m ). To overcome the lack of a high-pressure equation of state for sulfur, we model shock propagation in a basaltic matrix considering sulfur as a minor component. The amount of molten sulfur is then estimated in a second step using available thermodynamic constraints for the native element. Our simulations demonstrate that the meteoritic impact may produce an amount of molten sulfur consistent with Curiosity observations only for a significantly sulfur-enriched impact substrate (S > 10 wt % ). We find that impact velocity is an important factor: lower velocities favor the retention of a liquid melt pool, while higher velocities promote ejection and extensive vaporization. This study establishes meteoritic impact as a viable mechanism to produce deposits of pure native sulfur from sulfur-bearing soils on Mars.