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11 Facts About Mercury (the planet)

Last Reviewed and Updated on June 14, 2022

The planet Mercury is the smallest and innermost planet in our solar system. It moves faster around the sun than any other planet, completing its orbit about every 88 days. These are just some of the quick facts about Mercury, read the rest and get to know this planet a little better.

1. Mercury is the smallest planet in our Solar System

Since Pluto was demoted to a dwarf planet, Mercury became the smallest planet in our solar system.

Mercury has a radius of 1,516 miles / 2,440km, which makes it about a third of the size of the Earth. Pluto, the former champion, is about half the size of Mercury.

2. It is the closest planet to the Sun

Mercury is the closest planet to the Sun, on average being only about 36 million miles / 58 million kilometers away from the Sun.

It takes light about 3 minutes to reach the planet.

3. It has the most extreme temperature fluctuations of all planets in our solar system

Days get extremely hot on this planet, and maybe surprisingly the nights get extremely cold.

Temperatures on Mercury can jump to 800 degrees Fahrenheit / 430 degrees Celsius by day and be as low as minus 290 degrees Fahrenheit / minus 180 degrees Celsius by night.

4. Mercury orbits the sun with the greatest speed

The closer the planets are to the Sun, the faster they orbit it.

If you are wondering why you might want to give read this explanation of why planets orbit the Sun.

As Mercury is the closest to the Sun, the speed at which it moves is the fastest of all planets in our Solar system.

This speed at which the planet moves is called orbital speed or orbital velocity. Mercury has an orbital velocity of 47.9 km/s. Earth for example has an orbital velocity of 29.8 km/s, and Neptune the planet furthest to the sun only maintains a speed of 5.4 km/s.

5. Mercury has no moons

Mercury is one of the two planets in our solar system that has no moons.

This little planet is just too close to the Sun, so having moons is not possible. The Sun’s strong gravity would pull them away from the planet.

6. Mercury is a terrestrial planet like Earth

Terrestrial. planets are planets that are primarily composed of rocks or metals. Mercury, Venus, Earth, and Mars are all terrestrial planets.

Other planets in our solar system are giant planets. Giant planets are defined by their much larger than Earth-size as well as their composition, which is usually volatile and not solid.

7. It is named after the Roman messenger god

Mercury was a Roman god of financial gain, commerce, eloquence, messages, communication, travelers, boundaries, luck, trickery, merchants, and thieves. Mercury was a good that was viewed as swift-footed (fast), the same as the Greek god Hermes, and because Mercury, the planet that moves the fastest, it was granted this name.

8. You could sometimes see the sun rise twice per day on Mercury

One of the coolest facts about Mercury? Absolutely! Mercury has a unique rotation as far as our Solar system goes. If you were on Mercury you would be able to sometimes see the sunrise, stop, reverse its course back towards the rising horizon, stops again, and then rise again and move all the way across the horizon where it sets.

This happens just prior to when Mercury is closest to the sun.

9. It once had active volcanoes

There is evidence of past volcanic activity on Mercury. Evidence of pyroclastic flows from low-profile shield volcanoes was observed.

10. A solar day on Mercury lasts longer than one Mercury year

This has to be one of the most interesting facts about Mercury! A day on Mercury is technically longer than a year. While it takes “only” 58.6 Earth days for Mercury to spin around its axis, it takes a lot more for the day – from one sunrise to the next sunrise to happen.

The sunrise to sunrise would be called a solar day, and it takes Mercury 176 Earth days to complete one solar day.

One Mercury year, the time it takes Mercury to orbit the Sun, lasts for 88 days.

11. It’s closest to the sun but isn’t the hottest planet

You would think being the closest to the Sun would guarantee you having the highest temperature. This isn’t the case. With the mean temperatures of 333°F / 167°C, Mercury is only the second hottest planet, with Venus (867°F / 464°C) taking the first place.

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