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What Is the Planet Mercury?
March 30, 2011
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Mercury is a planet in our solar system. It is the smallest of the eight planets. It is also the closest to the sun. Mercury goes around the sun the fastest of all the planets. Mercury has no moons.

How Did Mercury Get Its Name?
The Romans believed that gods and goddesses were in charge of everything on Earth. Mercury is named after the messenger for their gods. The Roman Mercury had wings on his helmet and shoes. He could travel very quickly from place to place. The planet Mercury moves quickly around the sun. That is how it got its name.

How Big Is Mercury?
Mercury is a little bigger than Earth's moon. It is made of heavier materials, like iron. But if you could weigh Mercury and the moon, Mercury would weigh a lot more. Mercury is heavy, but it is small. It would take more than 18 Mercurys to be as big as Earth.

Where Is Mercury?
Mercury is the closest planet to the sun. Mercury goes around the sun once every 88 Earth days. A day on Mercury lasts a lot longer than a day on Earth. One day on Mercury lasts 59 Earth days.
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What Is Mercury Like?
The surface of Mercury looks like Earth's moon. It is covered with holes. The holes are called impact craters. The craters were made by rocks falling from space. The rocks are going very fast when they hit Mercury. A hole is made where the rock hits. Earth has a blanket of air around it. Mercury does not. The blanket is what helps keep Earth from getting too hot or cold. Because it is so close to the sun, Mercury can be very hot. At night, Mercury gets very cold. We could not live on Mercury!

How Has NASA Studied Mercury?
Mercury is hard to study because it is so close to the sun. People have never gone to Mercury. Spacecraft without people have gone. Mariner 10 was the first to visit Mercury. It flew by in 1974 and 1975. Not even half of Mercury was seen then. After that, nothing was sent to Mercury for more than 30 years. NASA's MESSENGER spacecraft flew by Mercury in 2008 and 2009. In March 2011, it began to orbit Mercury. MESSENGER will study parts of Mercury that have not been seen before. It will let scientists learn many new things about the planet.

More About Mercury:
› Space Place in a Snap: The Solar System's Formation   →
› Solar System Kids: Mercury   →
› MESSENGER


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David Hitt/NASA Educational Technology Services

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The planet Mercury
This picture of Mercury was taken by NASA's MESSENGER spacecraft.
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NASA
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Artist's drawing of MESSENGER in front of Mercury
MESSENGER has given scientists a better look at Mercury than they've ever had.
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NASA
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Page Last Updated: January 27th, 2014
Page Editor: NASA Administrator