Craters: Craters are the most prominent surface feature on Mercury, as they are on the Moon. Furthermore, all craters on Mercury exhibit the same morphological properties as those on the Moon. In fact, many have suggested that most of the craters on Mercury were created by impacts from space. An exception to this is the large number of apparently fresh craters in the Amazonian region of the planet's southern hemisphere.
Rivers: Many scientists believe that much of Mercury was once covered in water. Analysis of the data returned by MESSENGER has confirmed that parts of the planet's surface were indeed under water for at least several hundred thousand years ago. Studies of the distribution of these ancient shorelines have revealed a very different picture to the one seen on Earth or Mars. On Mercury, floodwaters did not cause global erosion but instead carved valleys and left behind a thick crust of rock that preserved evidence of what had been under the surface.
So, rivers can be expected to play an important role in the dynamics of Mercury's surface. The MESSENGER spacecraft has provided new information about two large systems on the planet's surface: Mariner Valley and Syrtis Major. These river systems are thought to have been flowing long ago because their valleys contain a high concentration of rock debris that was probably carried there by water.
Mercury's surface is similar to that of Earth's moon, with many impact craters caused by impacts with meteoroids and comets. The most prominent feature on Mercury's surface is Marius Hills, a group of large hills approximately 50 miles (80 km) across. They are formed from a mixture of rock types, including some that appear to be basalt and others that seem to be granite.
Like the Moon, Mercury has a thin veneer of earth-like materials called regolith that was once covered by ice. But while the Moon's surface has been altered by time and gravity, making some areas more useful for astronomy than others, Mercury's surface is still relatively unchanged by human activity or natural processes. The only exception may be some changes induced by the formation of its central peak, which may have involved volcanic activity.
The best known feature on Mercury is probably Calvario Hill, one of the highest points in the planet's orbit. It is 2,560 feet (790 m) high and has a base diameter of about 10 miles (16 km). Because it is taller than any other hill on Mercury, scientists think it may have been exposed to less erosion than other parts of the planet's surface.
It has several impact craters. Mercury is virtually completely devoid of atmosphere. Mercury's dark side is that it is extremely cold since it has practically no atmosphere to hold in heat and keep the surface warm.
There are two different types of craters on Mercury: high-latitude and low-latitude. High-latitude craters are found at the highest latitudes, where the sun always shines directly over the pole. Low-latitude craters are found at lower latitudes, where the sun sometimes shines directly over the equator. The reason for this difference is that near the north and south poles, the planet turns upside down relative to Earth-based observers; therefore, high-latitude objects appear as low-latitude features from their perspective. Objects at the same latitude but at different longitudes do not show this effect because they are moving away from or toward the observer at different speeds. Thus, both high- and low-latitude objects appear equally bright from Earth.
Crater shapes on Mercury can tell us a lot about how it was formed. On Earth, glaciers carve out wide, flat-bottomed valleys when they flow over rocks such as granite. As they move farther and faster, they can cut deeper and more dramatic gorges. This is what happened with the last major ice age, which ended about 10,000 years ago.