Impact-Induced Sulfur Melting on Mars: A Potential Source of Native Sulfur Detected by the NASA’s Curiosity Rover

NASA’s Curiosity rover recently discovered decimeter-sized clasts of nearly pure native sulfur within the Gediz Vallis channel in Gale crater, representing the first detection of elemental sulfur on Mars. The origin of this material remains uncertain, as native sulfur on Earth typically forms in volcanic, hydrothermal, or evaporitic environments. Here, we investigate a formation mechanism in which sulfur-rich material is melted by a meteoritic impact, producing molten sulfur that subsequently flows and solidifies at the surface. Geological mapping of the Gediz Vallis region reveals a partially breached crater (~390 m in diameter) located upstream of the sulfur-bearing deposits, within a light-toned yardangs unit. We interpret this structure as a candidate source crater, where impact-generated melt may have escaped through the breach and flowed a few kilometers downslope before solidifying. Production of melt in the context of such a small impact crater is qualitatively supported by the observations of impact melt pools associated with small craters on Lunar basaltic surfaces.

To assess whether the volume of melt produced could be comparable to the native sulfur deposit at Geidz Vallis, we performed numerical simulations using the iSALE shock-physics code. We modeled vertical impacts of dunite projectiles into a basaltic target at velocities of 5, 7, 10 km/s, the size of the asteroid being empirically adjusted to reproduce  the observed crater size. Because a dedicated high-pressure equation of state for sulfur is unavailable, sulfur was treated as a minor component of the target, and shock propagation was assumed to be controlled by the basaltic matrix. Sulfur melting was then evaluated a posteriori using reconstructed thermodynamic properties derived from experimental shock data and melting curves.

From tracer-based shock pressure histories, we estimated the total mass of sulfur melted (liquid plus vapor), the fraction retained within the crater as a melt pool, and the amount potentially lost to vaporization. Our results show that total melt production increases with impact velocity, while only about 20–25% of the melted sulfur is retained within the crater after excavation. For sulfur concentrations typical of minor components, the retained melt mass is insufficient to explain the volume inferred from Curiosity observations. However, extrapolation to sulfur-rich substrates (≥ 50% sulfur fraction) would yield melt pool masses comparable in order of magnitude to Curiosity’s inferred mass, even under conservative assumptions regarding vaporization and ejected melt.

These results suggest that impact-induced melting of sulfur-rich materials is a possible mechanism for producing native sulfur deposits on Mars, provided that the light-toned yardangs unit is significantly enriched in sulfur. However,  a model  incorporating a dedicated sulfur equation of state is critical to further test this hypothesis, whereas in situ rover observations as Curiosity approaches the yardangs unit shall reveal its nature and composition.