Mercury's surface resembles that of the Earth's moon. It's riddled with holes. The holes are referred to as "impact craters." The craters were formed by rocks that fell from space. These impacts have been damaging Earth's closest companion for most of its history.
Over time, solar wind particles and cosmic rays have penetrated the thin veneer that covers Mercury's surface. This has exposed many rock layers that can be found just beneath the surface. These layers were created over millions of years by volcanic activity and the deposition of sediment.
The depth of these layers on Mercury is hard to estimate because most of them are buried under hundreds of feet of lava. However, scientists think they may reach depths of up to 14,000 feet (4,270 m).
The image you see here was taken in 1990 by one of NASA's two MESSENGER spacecrafts. You can see parts of the American Midwest and Rocky Mountains. The image has been colorized using data from MESSENGER's EDGE spectrometer to reveal details invisible to the human eye.
MESSENGER is currently in orbit around Mercury taking measurements of the planet's internal structure and environment.
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. These features were formed when portions of Mars' atmosphere or earth's atmosphere collapsed into their surfaces with great force.
Like the Moon, Mercury has a thin veneer of soil over rock that may be as old as 4 billion years but was probably created much more recently by impacting objects. The best example of this is the famous Schooner Horatio Nelson, which traveled 200 miles after being launched from its home port in England in 1770. It now lies on its side more than 300 miles from any land mass, having been blown off course while traveling west with the wind.
The core of Mercury is extremely dense: 3.5 times that of iron. This is because most of the mass of the planet is made up of hydrogen and helium, which are both light and abundant. The only other element that accounts for more than 1% of Mercury's mass is nickel, which makes up 0.4%. All the other elements account for less than 1% each.
Mercury resembles Earth's moon in appearance. Mercury's surface, like our moon's, is riddled with craters created by space rock strikes. Mercury has a strong iron core and a thinner rocky crust on the outside. Like Earth, Mercury has two almost equal sides turned toward the Sun (equal temperatures) and two that are cold (toward the center of the planet).
The Earth's moon is always dark because of lack of sunlight, but mercury has a very thin atmosphere to allow some light from behind to reach it. Most of the time, it is completely darkened by nightfall.
The only place on Mercury where you might see stars is in the sky around Meridional Meridian East, where there are few clouds and no darkness due to daytime sunrises and sunsets.
You can watch videos of Mercury here: https://www.youtube.com/watch?v=1qohy0VZUQ8. The first video is from the Messenger spacecraft which was sent to orbit Mercury from 2004-2011. The second video is from the MESSENGER Reentry Mission in 2018.
Mercury has a thin atmosphere of atoms that have been blasted off its surface by solar radiation. This atmosphere swiftly escapes into space and is renewed on a regular basis. The composition of this atmosphere is unknown but it probably contains hydrogen, helium, and traces of other elements.
Like the Moon, Mercury has been altered by water ice which lies beneath its crust. The evidence for this comes from data collected by NASA's Mariner 9 spacecraft, which revealed that parts of Mercury have a higher density than others. These regions include many of the large volcanoes, which must be rich in silicon dioxide (silica) because they are so dense.
The most famous feature of Mercury is its orbit around the Sun. Because it is such a small body orbiting so far away from the rest of the planets, its orbit is significantly affected by the gravitational pull of Mars, Jupiter, and Saturn. As a result, Mercury's eccentric orbit varies between about 55 million km to 63 million km from the Sun. This is much closer than Earth's orbit, which ranges from approximately 149 million km to 575 million km from the Sun!
Mercury was once thought to be a completely different planet from Earth, but this view changed after data were collected by several missions over several decades.
Mercury's surface resembles that of the moon, and the planet is most likely composed of the same kind of rocks and dust. Both worlds have impact craters on their surfaces, but Mercury's Caloris Basin is one of the largest in the solar system. It measures 5500 miles across and was created when a large object, probably a rock from outside the solar system, hit the planet about 3 billion years ago.
Like the moon, Mercury has no magnetic field, which means it can be affected by Earth's atmosphere and weather. So any exposed surface material on Mercury that has air above it (such as that in crater walls) will be slowly eroded over time by wind gusts that blow through the atmosphere. The direction of these winds varies by location, but they usually come from the west. Crater floors also collect water vapor from the atmosphere, which condenses into liquid rain or snow that flows into those same craters.
Some craters may contain small lakes within them. If so, they might be able to preserve biological materials such as pollen or DNA from ancient organisms. So far, no such bodies have been found on Mercury. However, many scientists believe that life may have arisen on Mercury at some point in the past.
Images taken by Mariner 10 during its last flight over the planet in 1974 revealed that there are several large smooth areas on Mercury's surface.
Mercury, along with Venus, Earth, and Mars, is a rocky planet. It, like our Moon, has a solid surface covered with craters. However, because Mercury is so much closer to the Sun than we are, it experiences much more intense heat and pressure, which causes its surface to change quickly. The most recent impact site we know about was created only 400,000 years ago.
Like the Moon, Mercury has many old crater walls that were formed when parts of its surface broke off and was later lost from view. These include broad, flat-topped formations called mare surfaces, which are found mainly in the far side of the planet from where we observe it. They may be as large as 500 km across. There are also several small crater groups called arcae that appear as dark spots on some images of Mercury's surface. They are thought to be collapsed volcanic tubes.
We know about most major features on Mercury from studies by the Mariner 10 spacecraft, which made three flights by NASA between 1974 and 1991. On each flight, the spacecraft flew over most of the planet at an altitude of 100 miles (160 kilometers). Data from these missions have helped scientists understand more about how planets are formed and evolved.