How do modern atmospheric processes continue surface rusting without significant standing liquid water?

UV radiation breaks down $ ext{H}_2 ext{O}$ and $ ext{CO}_2$ into reactive oxygen radicals

Because the modern Martian surface is extremely arid, ongoing oxidation must rely on mechanisms not dependent on standing liquid water. The current atmospheric composition, thin as it is, contains water vapor and carbon dioxide ($ ext{CO}_2$). A proposed mechanism involves intense ultraviolet radiation from the Sun striking the atmosphere. This radiation possesses enough energy to break apart water molecules ($ ext{H}_2 ext{O}$) and carbon dioxide, generating highly reactive components, specifically oxygen radicals. These radicals then chemically attack the exposed iron-bearing minerals on the surface, allowing for a slow, steady process of rusting to occur in place, known as *in situ* oxidation.