What is the Planet Mercury? | Types, Definition, Structure, Function & Facts
What is Mercury like?
Now that Pluto is no longer classified as a planet, Mercury is the smallest planet in the solar system. Mercury has a rocky surface and an iron core. Mercury’s iron core is huge compared to other rocky planets like Earth and Mars. This makes Mercury’s mass very high for its size. Mercury is a barren planet covered in craters caused by asteroid impacts and other objects. It looks a lot like Earth’s moon.
Mercury has almost no atmosphere and rotates very slowly relative to the sun. One day on Mercury is equivalent to almost 60 days on Earth. Due to its long days and small atmosphere, Mercury has extreme temperatures. The side facing the sun is extremely hot (800 degrees F), while the side away from the sun is super cold (-300 degrees F).
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Highlights of Planet Mercury:
| Moons | 0 |
| Mass | 5.5% of Earth |
| Diameter | 3031 miles (4879 km) |
| Year | 88 Earth days |
| Day | 58.7 Earth days |
| Average Temperature | 800°F (430°C) during the day, -290°F (-180°C) at night |
| Distance from the Sun | 1st planet from the sun, 36 million miles (57.9 million km) |
| Type of Planet | Terrestrial (has a hard rocky surface) |
How does Mercury compare to Earth?
Mercury is much smaller than Earth. It’s actually much closer to the size of Earth’s moon. He has a shorter year, but a much longer day. There is no air to breathe and the temperature varies greatly every day (even if the day is very long!). Mercury is similar in that it has a hard rocky surface like Earth. You can walk on Mercury if you have a spacesuit and can withstand extreme temperatures.
How do we know about Mercury?
There is evidence that the planet Mercury was known as far back as 3000 BC by civilizations such as the Sumerians and Babylonians. Galileo was the first to observe Mercury through a telescope in the early 1600s. Since then, a number of other astronomers have added to our knowledge of the planet.
Since Mercury is so close to the Sun, it is difficult to send spacecraft to explore the planet. The sun’s gravity is constantly pulling the spacecraft, making it need a lot of fuel to stop or slow down at Mercury. Two space probes have been sent to Mercury. The first was Mariner 10 in 1975. Mariner 10 gave us our first close-up images of Mercury and discovered that the planet has a magnetic field. The second space probe is MESSENGER. MESSENGER orbited Mercury from 2011 to 2015 before crashing into Mercury’s surface on April 30, 2015.
Mercury is difficult to study from Earth because it lies inside Earth’s orbit. This means that when you try to look at Mercury, you are also looking at the Sun. The bright sunlight makes it almost impossible to see Mercury. For this reason, Mercury is best seen right after sunset or just before it rises.
Interesting Facts about the Planet Mercury
Mercury has a huge crater called the Caloris Basin. The impact that caused this crater was so great that it formed hills on the other side of the planet!
The element mercury is named after the planet. Alchemists used to think they could make gold out of mercury.
This planet is named after the Roman god Mercury. Mercury is the messenger of the gods and the god of travelers and merchants.
Mercury orbits the Sun faster than any other planet.
Greek astronomers initially thought they were two planets. They called the person they saw at sunrise Apollo and the person they saw at sunset Hermes.
It has the most eccentric (least circular) orbit of all the planets.