Dark material on Vesta may consist of carbonaceous chondrite-like material delivered by impact events.
This study uses hypervelocity impact experiments to assess the viability of the impact delivery hypothesis.
Experiments reveal that impact events deliver significant fractions of the projectile to the target
during impacts at average vestan speeds. Hence, dark material can plausibly be delivered to Vesta by
impacts, with the projectile component accumulating in the regolith with time. Projectile retention is
sensitive to impact angle, ranging from 7% for 30 impacts (measured from horizontal) to 72% for vertical
impacts. Averaged over the probability distribution of impact angles, 17% of the projectile’s mass remains
in or near the crater. Projectile-contaminated breccias largely remain inside the crater for vertical
impacts. In oblique impacts, projectile-contaminated pieces concentrate downrange beyond the crater
rim. Based on experiments, projectile delivery is expected for typical vestan impact conditions, not only
for extraordinary events such as low-probability and very low-speed (e.g., <2 km s1) impacts. These
experiments indicate that other (non-dark) impactors contaminate the vestan regolith. Regolith-laden
bodies in environments with similar impact speeds also may accrete significant amounts of foreign
debris.
