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Facts About Mercury

1 Orbit of Sun
87.969 Days
1 Rotation
58.6461 Days
5% of Earth
5% of Earth
Escape Velocity
15,450 km/h (9,600 mph)
Distance From Sun
57 million kilometers (36 million miles)
Max Temperature
465°C (870°F)
Min Temperature
-184°C (-300°F)
Hydrogen, Helium
4,876 kilometers (3,030 miles)

Did you know?

Mercury’s orbit is not a perfect circle like most of the other planets. It’s actually egg-shaped. At times, Mercury’s orbit brings it closer to the Sun than other times, while all the other planets that have circular orbits are always the same distance from the Sun.

The planet Mercury is the closest to the sun and the quickest to revolve around it. It’s a very dense planet with a solid iron core and a thick crust. That said, Mercury is small overall and so has weak gravity. It can’t even hold onto an atmosphere! This makes it unable to regulate its temperature such that it fluctuates dramatically.A telescope image of Mercury.

Here are Some Facts About Mercury

How Did Mercury Get its Name?

In Roman mythology, Mercury was the messenger of the Gods. He was super quick, often depicted wearing winged sandals. Likewise, Mercury is the fastest of the planets. Its orbit of 88 days is the shortest in our Solar System.

An image of the foot of a statue of the god mercury, wearing his winged sandals.

Mercury’s winged sandal. Fast, but by no means fashionable.

A Dense Planet

Despite its speed, Mercury is awfully dense. The inside of the planet is almost entirely iron, either solid or in the form of magma. The earth’s core has a similar makeup, but it also has a large mantle which Mercury does not. Instead, it has only two very thin layers above the core.

This imbalanced structure has to do with how the Solar System is arranged. Planets on the inside, like Mercury and Venus, are metallic and rocky. That’s because, long ago, the sun pushed away or destroyed anything lighter. Gas got thrown outwards, and any ice close to the center melted. Mercury, the closest planet to the sun, has none of these things. It’s pretty much just metal.


Rocky asteroids, full of metal. Mercury was built by their constant collision.

Mercury has a Wrinkle!

Like the layers of the Earth, Mercury’s layers interact with each other. Yet, as Mercury’s core is by far the largest and most powerful layer, these interactions aren’t what we might expect.
The most significant of them is core shrinkage. Mercury’s outer core is liquid, similar to the earth’s. But, it’s also cooling slowly. As solids are denser than liquids, this means that the planet’s core is getting smaller over time.
In fact, the whole planet is shrinking as compression of Mercury’s inner layers pulls the top ones down. Of course, its crust is a solid and can’t just ‘shrink.’ Rather, it gets crushed up as it descends. This has lead to the creation of what we call lobate scarps on the planet’s surface. These odd landforms are basically just wrinkles in the crust.

An image of a wrinkle, or scarp, on Mercury's surface.

The wrinkle in the center of this photo is a lobate scarp.

Mercury Has No Atmosphere

Another notable feature about Mercury is that it has no atmosphere. That means it doesn’t trap gas around it; it has no air.’ This is the result of two things. The first is pretty simple. Although mercury is dense, it doesn’t have a lot of mass overall. As a result, it has weak gravity and can’t hold things down very well. In fact, if you went there, you would only weight about ⅓ as much as you do on earth.
The second reason Mercury has no atmosphere has to do with the sun. The sun emits lots of radiation as part of what’s called solar wind. On earth, our atmosphere protects us from these winds in a sacrificial manner. The wind destroys our atmosphere instead of hitting us.
 An image of beams of sunlight filtering through clouds.
Although light gets through our atmosphere, solar wind does not. This filtering saves our lives every day!

Temperature Extremes

For many planets, having an atmosphere allows them to trap heat. This keeps them within a certain temperature range. But of course, Mercury doesn’t have an atmosphere. Its temperature depends upon its exposure to the sun. 
On the side that’s facing the sun, things can get really hot. The surface climbs to temperatures of up to 870 degrees Fahrenheit! Oppositely, Mercury’s dark receives very little heat. It can become as cold as -300 degrees Fahrenheit. 

Other Great Resources:

NASA’s Space Place on Mercury:

(Video) Overview of the Planet Mercury:

(Video) Crash Course on Mercury:

NASA Probe Crashes into Mercury:

Written by: Noah Louis-Ferdinand