Mercury Facts for Kids

Are you fascinated by our solar system? Do you have a favorite planet? Maybe you like the planet Earth since that is the planet we live on or maybe you like Saturn for its beautiful rings, but have you ever stopped to think about the planet Mercury. Mercury has been the smallest planet in our solar system since 2006, when Pluto was re-classified as a dwarf planet. Although Mercury is closest to the sun, it is the second hottest planet, beat out by it’s neighbor, Venus. Mercury is known for having extremely high temperatures and a crazy long day! If any of that interests you, Mercury may be the planet for you! But, before you relocate keep reading these Mercury facts for kids to find out just how hot the surface is and how long a day lasts because you might just reconsider.

The Size of Mercury

1. Mercury is the smallest planet in our solar system. It has a radius of only 2440 kilometers (1,516 miles). That seems like a lot, but in comparison to other planets, it’s really not. For example, the size of Earth is about three times the size of Mercury with a radius of 3,958 miles and that’s not even the biggest planet! Can you imagine how large Jupiter’s radius is? Almost 45,000 miles! Compare that to the size of Mercury.

2. Mercury is the second densest planet, second only to Earth. It has mass of 3.3 x 10^23 kilograms (7.3 x 10^22 pounds) and a radius of about 1,500 miles.

Mercury Facts for Kids – The Surface of Mercury

3. Mercury is a terrestrial planet, also known as a rocky planet. The four other terrestrial planets include Earth, Venus, and Mars. These are the four planets closest to the Sun.

4. Mercury’s surface is covered in a thin layer of dust and rocks called the “regolith.” The regolith is thought to be made up of material that was blasted off Mercury’s surface by comets and asteroids hitting the planet.

5. Did you know you can see the rocky surface of Mercury using a telescope? That’s right! Mercury is easiest to spot in the morning sky between October 3rd and October 17th and is easiest to see in the night sky between April 18th and May 10th. Have you ever seen Mercury?

Mercury’s Atmosphere

6. Mercury has a very thin atmosphere. Because of it’s thin atmosphere, mercury experiences a range of extreme temperatures. The surface temperature at night can drop to -173 degrees Celsius, or -279 degrees Fahrenheit! On average, the daytime temperature of Mercury is 427 degrees Celsius, or 800 degrees Fahrenheit. That’s over a 1000 degree jump in just one day, according to the Fahrenheit scale. Wow!

7. Mercury has the most cratered surface of any planet in our solar system. It is thought to have been hit by over 100,000 comets and asteroids!

8. Mercury has very thin clouds of vaporized metals, including sodium and potassium, which are thought to form when Mercury is hit by the solar wind – a stream of particles ejected from the sun.

Mercury Facts for Kids – Where is Mercury?

9. Mercury is the closest planet to the Sun with just 40 million miles separating the planet from the star.

10. Since Mercury is so close to the Sun, we cannot see it with the naked eye. You need a telescope to see the small planet from Earth.

Mercury’s Orbit

11. Mercury has a very elliptical orbit, meaning that it is often closer to the sun than it is at other times. When it is closest to the sun, it is said to be in “perihelion.” When it is furthest away from the sun, it is in “aphelion.” Fun fact: Mercury has the longest perihelion of any planet in our solar system!

12. Mercury’s day is longer than its year! One day on Mercury lasts for 176 Earth days, while one year on Mercury only lasts for 88 Earth days.

Mercury Facts for Kids – Characteristics of Mercury

13. Despite being so close to the sun, Mercury is actually quite dark. Its surface reflectivity (or “albedo”) is only 0.11, meaning that it reflects less than 12% of the light that hits it.

14. Mercury has a very weak magnetic field, only about 1% as strong as Earth’s.

15. Mercury has the smallest amount of water of any planet in our solar system – just 0.0001% by volume!

16. Did you know Mercury has no moons? This is different from the planet Earth, where we see our moon each night.

Mercury’s Core and Compounds

17. Despite its small size, Mercury has the second largest molten core of any planet in our solar system, after Earth. The core of Mercury is mostly iron and it makes up about 42% of its total volume!

18. Some mercury compounds were once used in things like mercury lamps, mercury thermometers and mercury fever thermometers. However, these uses have now been banned in many countries because mercury is poisonous.

More Fun Facts About Mercury!

19. Mercury is named after the Roman god of commerce, travel and thieves.

20. The symbol for mercury is a cross with two curved lines on top. This is called a caduceus and is also the symbol for medicine and doctors.

21. In ancient times, mercury was used in a process called “gold amalgamation” to extract gold from ore.

Mercury Facts for Kids – Expeditions to Mercury

22. Mercury is not an easy planet to visit! There have only been two successful missions to mercury – Mariner 10 in 1974 and Messenger in 2004.

23. Mariner 10 was the first spacecraft to visit mercury, and it sent back over 7200 images of the planet!

24. The Messenger spacecraft became the first spacecraft to orbit mercury when it arrived in 2011. It sent back over 250,000 images of mercury before crashing into the surface of the planet in 2015.

There are currently no plans for another mission to mercury, but scientists hope that one day we will be able to send a spacecraft to land on mercury and study it in more detail. Would you ever want to be aboard one of those rocket ships?


Check out these fun facts for kids here and browse all the other topics at the bottom of the post.

Read Solar System Facts for Kids and download a FREE printable packet.