Do you know that Mercury has almost no atmosphere? This explains why so many meteorites crash into Mercury’s surface. With all this crashing activity, it is surprising that Mercury remains in one piece and continues to be part of our solar system.

How Did Mercury Get Its Name?

Mercury orbits around the sun very quickly (in 88 Earth days), so the ancient Romans named it after the Roman God of speed, Mercury.

A Thin Atmosphere

Mercury has a thin atmosphere. Most of the gases it once had became so hot that the gas particles moved so fast, they escaped the planet’s gravitational pull and moved into outer space.

Mercury’s atmosphere is very different than Earth’s. While Earth’s atmosphere is very thick and is mostly nitrogen and oxygen, Mercury’s atmosphere is very thin and made up of mostly sodium. Humans could not survive by breathing sodium gas. They require both oxygen and nitrogen to survive. Although the atmosphere on Mercury contains a small amount of oxygen, without the presence of nitrogen, human life cannot exist. Nitrogen contains amino acids, which are the building blocks of protein. Without protein, a human body cannot repair itself, grow, move, reproduce, digest, and age.

On the side of Mercury that is facing the Sun, the surface is baked by the Sun’s extreme heat. As a result, the hottest temperature on Mercury reaches up to 800 degrees Fahrenheit. Because of the thin atmosphere, most of this heat can escape into space at night. Therefore, the temperature goes down to –300 degrees Fahrenheit on the side of the planet facing away from the Sun. Because of its thin atmosphere and lack of water, Mercury has no clouds or wind.

Chances are, humans will never live on Mercury. The sun’s heat and lack of oxygen and nitrogen prevent man from ever living on this planet. Even if man were to find a way to live there, he would need to transport water, oxygen, and food from Earth, and this would be very expensive.

Inside and Out

Mercury is made up of three main layers - the crust, the mantle, and the large iron core. The crust is full of craters and cliffs. Like Earth, the mantle is made up of thick layers of lava rock. The core is a large ball of iron.

Mercury’s surface is mainly covered with craters, tall cliffs, and large flat plain areas. The craters were created by meteorites that crashed into its surface. These chunks of rock have been 

crashing into Mercury for billions of years. It is believed that many of these craters were created 4 billion years ago, around the time our solar system was formed. Back then, the solar system was full of meteorites varying in size from tiny pebbles to massive boulders having a diameter of 1,000 feet. In contrast, Earth’s surface does not have nearly as many craters as Mercury because it has such a thick atmosphere. The heat and the friction in the Earth’s atmosphere destroyed most of the meteorites before they hit the Earth. With all of the craters on its surface, Mercury looks a lot like the surface of Earth’s moon.

Large craters on Mercury’s surface are called basins. The Caloris Basin is the largest and most well known geographical feature on Mercury. This huge basin is one of the largest craters in our solar system.

Did you know that around 60 percent of Mercury’s surface is covered with large, flat plains? These plains are known as planitia, or seas as they are called on the moon. It is unknown how these were formed. Many scientists believe they were formed when lava from the mantle forced its way to the surface through cracks or holes and was somehow smoothed and dried.

Many steep cliffs, called scarps, are also located on Mercury’s surface. Scarps are large, long, rounded cliffs that range from 1,000 feet to 2 miles high. The length of scarps are from 10 to 300 miles long, or about the distance from Detroit to the Mackinac Bridge. This feature is unique to Mercury, since no other planet or moon in the solar system has these types of formations. Although there are cliffs on Earth, they are nothing compared to the cliffs on Mercury.

Mercury’s extremely large core is made up of iron. For its small size, this planet contains a large amount of iron. No one really knows how this large iron core could have formed. Many scientists think that when Mercury was in its early stages of formation, it crashed into another planet whose core contained a large amount of iron.

Exploration

In 1973, Mariner 10 was the first spacecraft to explore Mercury up close. Its mission revealed many interesting facts about Mercury. Mariner 10 took many pictures of Mercury’s craters, basins, scarps, and plains. Scientists also learned much about these landforms by sending radar waves to Mercury’s surface. The equipment used by Mariner 10 allowed them to figure out the characteristics of these landforms by measuring the amount of time it took for the radar waves to bounce back to the spacecraft.

Mariner 10 was also the first spacecraft to use gravity from another planet to get to another destination. It also used the Sun’s solar-powered wind to gain speed. When Mariner 10 was running low on fuel, it opened up its large solar panels to catch the Sun’s solar wind. This is similar to a sailboat opening up its sails to catch the wind and pick up speed.

Mariner 10 turned out to be a very important mission. Mankind learned more about Mercury’s characteristics and geographical features in one year than it had in the past 5,000 years!

Transit

From time to time, the orbit of Mercury will pass directly between the Earth and the Sun. When this happens, you can see Mercury pass in front of the surface of our enormous Sun.  This is called a transit.

A Short Orbit

Mercury is the fastest orbiting planet in our solar system. It only takes 88 Earth days to travel around the sun. This is quite fast compared to Earth and the other planets in our solar system.

A Long Rotation

Like all planets, Mercury spins around on its axis. An axis is an imaginary line that runs directly through the planet. It takes Mercury 58.7 Earth-days to rotate once on its axis. This is very slow compared to Earth, which rotates once in 24 hours or one day.

Showing Phases

As Mercury makes its way around the Sun, it appears to change in shape and size. When this happens, it is called a showing phase. Its size, as it appears from Earth, is always changing because its distance from Earth is always changing. Although the shape of Mercury appears as if it is constantly changing, it really is not. It only appears to change because of the way the Sun’s light hits Mercury. It is important to note that Mercury does not give off any of its own light. It only reflects light from the Sun. This is another reason for Mercury’s changing shapes. Because this planet is so small and so far away, its showing phases cannot be seen with the naked eye, but only through a telescope.

To Sum It Up…

Although Mercury is one of the smallest planets in our solar system, its geographical characteristics make it very interesting. It has a very thin atmosphere and temperatures that can range from 800 degrees during the day to -300 degrees Fahrenheit at night. Almost everything we know about this small planet is from the Mariner 10 mission. Hopefully, as technology improves, more spacecraft will be sent to Mercury so mankind can learn more about the many still unanswered questions.

Basic Facts

Kerrod, Robin. Mercury and Venus. Minneapolis: Leener Publications, 2000.

Space: Everything You Need to Know and Beyond! <http://library. thinkquest.org/J0112388/> Last visited: December 2001.

Space: Today, Tomorrow, and Always.</J0112188/> Last visited: December, 2001.

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