What characterizes the smooth plains on Mercury?

The smooth plains on Mercury are characterized by their relative lack of craters compared to other regions of the planet. These plains were formed by volcanic activity, which has filled in the older cratered surfaces over time, resulting in a smoother appearance. This process not only covered existing craters but also created a more uniform surface.

The lack of craters on these smooth plains indicates a younger geological age compared to the heavily cratered parts of Mercury, which shows that volcanic activity was more prominent in these areas. This relatively smoother and less cratered terrain provides important clues about the geological history of Mercury, illustrating the dynamics of surface processes on the planet.

Other options do not accurately describe the characteristics of the smooth plains. For instance, the presence of ice is not a defining feature of these plains, nor do they exhibit jagged features and ridges, as would be found in more geologically active or older terrains. Additionally, while the plains may not have as many craters, other regions of the planet are older, making the statement regarding their age incorrect.