How did the smooth plains on Mercury form?

The smooth plains on Mercury predominantly formed by lava flows that erupted following the Caloris Basin impact, one of the largest impact craters in the solar system. When the massive impact occurred, it created significant energy that melted the underlying rock and allowed magma to rise to the surface. This lava then spread out to fill in low-lying areas, creating the smooth plains we observe today. The result was extensive basaltic plains, similar to those found on the Moon, but distinct in their formation due to the influence of the Caloris event.

The formation of these plains is primarily linked to volcanic activity triggered by the immense forces of the impact, which contrasts with other processes such as sediment deposition, which involves layering over time and would not create the same smooth surface. The idea of repeated volcanic eruptions is less accurate as the primary formation event correlates specifically to the Caloris impact, rather than ongoing volcanic activity across an extended period. Additionally, processes like wind erosion play a negligible role on Mercury due to its thin atmosphere; therefore, it cannot account for the vast, smooth plains observed. This understanding emphasizes the impact of specific geological events on the morphology of planetary surfaces.