What evidence do we have that the surface features on Mercury were not formed during recent geological history?

Mercury, often likened to Earth's moon due to its cratered appearance, provides a historical record of the solar system's past. The high density of impact craters on Mercury's surface is indicative of a turbulent early solar system, where frequent collisions were commonplace. These craters vary in size and complexity, from small, simple pits to larger, more complex structures with central peaks and terraced walls.

Over time, the rate of crater formation has slowed significantly, and the persistence of these ancient craters indicates a lack of recent resurfacing events that could erase or modify them. By studying the distribution and characteristics of impact craters, scientists can deduce the age of different planetary surfaces, with a more cratered landscape suggesting an older surface.

Moreover, Mercury displays a lack of large-scale tectonic features like mountains and plate boundaries, which are common on Earth. This suggests that internal geological processes that drive tectonics on Earth have been inactive on Mercury for billions of years.

The formation of impact craters is a violent process that begins when a meteoroid, asteroid, or comet collides with a planetary surface. The energy released during the impact excavates a hollow, typically circular, depression into the surface. The impact generates shock waves that can produce a variety of features, including central peaks that form from the rebound of the planet's crust, and ejecta blankets that are composed of the displaced material.

Mercury's craters are largely preserved due to the planet's lack of atmosphere, which on Earth, would cause erosion and weathering that could eventually remove the evidence of impacts. The size and number of craters on Mercury also help researchers to understand the environment of the early solar system and the potential bombardment frequency celestial bodies faced. Furthermore, the distribution of craters can reveal underlying crustal properties and past geological activity, such as volcanic flows that may fill and modify existing craters.

Intercrater plains are expansive, relatively flat regions found on Mercury, nestled between larger impact craters. Their smooth appearance suggests that they were formed by widespread volcanic activity early in Mercury's geological history. Since these plains cover large areas and often obscure the underlying terrain, they provide clues that suggest the occurrence of volcanic resurfacing after the original crust had formed and was subsequently cratered.

The absence of new plains or significant overlying craters implies that the volcanic activity that created them ceased long ago. The intercrater plains also allow scientists to infer that Mercury, despite its small size and proximity to the Sun, had a geologically active past. The presence of these plains offers a basis for understanding Mercury's volcanic history and its gradual transition to the geologically dormant state we observe today.