It, like our Moon, has a solid surface covered with craters. It has no moons and has a scant atmosphere. Mercury prefers to keep things as simple as possible. Because Mercury rotates slowly in comparison to Earth, one day lasts a long time. 884 Earth days, to be precise.
Its orbit is almost exactly between Earth's and Sun's, which means it gets too hot for life as we know it and there is no water on its surface. But it's also very close to Earth, which helps to mitigate some of the problems with its orbit.
Mercury has one of the most eccentric orbits among the planets. It crosses paths with Earth about twice a year. The last time this happened was 2008, when an American spacecraft called MESSENGER flew by and took pictures from within 25 miles (40 km) of the planet's surface.
These images revealed great details about the planet's history of bombardment by objects from outside Earth's solar system. They showed that much of Mercury is still hidden beneath ancient layers of rock and soil. In fact, the entire visible surface was exposed only 10 million years ago!
Most of the rocks on Mercury are basaltic in nature, but there are also deposits of sulfur that formed under the influence of sunlight.
Mercury, along with Venus, Earth, and Mars, is a rocky planet. 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 more quickly. The impact of meteorites also adds to the destruction of the planet's surface.
Yes, Mercury has many craters. In fact, it is most heavily cratered body in the Solar System after the Moon. Because they are so deep and wide, some craters on Mercury are even visible from Earth with the naked eye! Although most of these features are obscured by solar radiation, several large peaks still rise above the surface. One of these is called Marius Hills, after the first person who identified it in 1609. He named it for his employer, King Louis XIII of France.
The best places to see these hills with the Earth's atmosphere are from within: They're invisible without the aid of telescopes.
However, there are a few spots where smaller features can be seen with the unaided eye. One such area is called the Lockyer Valley, which is centered around 75 degrees west longitude and 28 degrees south latitude.
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 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 gravity from any number of planets over time. The most recent addition to Mercury's body of knowledge was made possible by NASA's Mariner 10 spacecraft, which passed by Mercury in 1974 and 1992. Scientists were able to determine from Mariner 10 data that much of Mercury has changed color over time due to exposure to sunlight, similar to how Earth's moon changes hue during lunar eclipses.
The similarity between Mercury and our Moon isn't surprising considering they're both small, terrestrial bodies that used to be members of larger planetary systems. But even though they share many similarities, there are still important differences between them. For example, while the Moon always shows the same face to the Earth, Mercury can appear either side-on or upside-down when viewed from far away. Also, the Moon's orbit around Earth is almost exactly half of Earth's radius, but Mercury's orbit is only 43% as wide.
Another interesting fact about Mercury is that it moves closer to the Sun than does Earth.
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.
The Earth's moon is another planet that shows us how different they can be. The moon has been very important for understanding planets outside our own and also about gravity. It has been used as a training tool for astronauts going to Mars or other planetary bodies.
As well as being useful for space travelers, the moon is also responsible for many natural disasters here on Earth. Areas where the moon's influence is strong will have more meteorites hits and earthquakes than places where it is weak. But the moon's power to cause havoc is also its greatest gift because it gives us a window into other worlds.
Another example is Venus. This planet is almost exactly like Mercury but much hotter. As you might expect from such high temperatures, there is no water nor life as we know it on Venus. However, studies have shown that at one time probably not long after the solar system was formed, Venus may have had an oceanic world called Venus Island. This island would have been destroyed when the sun heated up Venus so dramatically that the sea evaporated.
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 mountains over 20 miles (30 km) across. These features were formed when portions of the surface were uplifted and then collapsed, like the hills after an earthquake on Earth.
Like Earth, Mercury has a thin atmosphere made up of gases such as sulfur dioxide and chlorine. However, because Mercury is so much closer to the Sun than Earth, its atmosphere gets evaporated every day. Only about 10% of the planet is covered by water, but it contains more iron than Earth's oceans. Iron-rich rocks are found everywhere on Mercury's surface, even in areas apparently far from any source of iron. The cause of this distribution is still not known with certainty, but it may have something to do with the early history of the Solar System.
The first evidence for water on Mercury came from observations by Mariner 9 in 1974. Although the spacecraft did not arrive at Mercury until three years later, scientists had already concluded that the observed features must be lakes or some other kind of body of water.
This image of Mercury's surface depicts the eroding process on the innermost planet. Mercury lacks these agents, and its atmosphere is far too thin to shield it from cosmic collisions.... An average-size asteroid impacts Earth every 100 years or so, but because Mercury is three times closer to the Sun, it experiences a large impact every 59 days or so.
The photo was taken by the MESSENGER spacecraft, which was launched in 2004 to study the planet Mercury. It entered orbit around Mercury on April 30, 2011, and will remain there until May 25, 2015, when it will begin its first extended mission. After that, it will use its remaining fuel to go into an elliptical orbit that will take it as close as 4 million miles (6 million kilometers) to the sun and as far away as 35 million miles (56 million kilometers).
As MESSENGER orbits Mercury, it takes pictures such as this one, which shows an area about the size of California near the planet's north pole.
The bright spots are craters, some of which are marked by lava flows from deep within the planet. The image was taken just before 3:00 a.m. on April 18, 2012, at a distance of approximately 485,000 miles (800,000 kilometers) from Earth.