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Mercury Facts For Kids

The planet Mercury is a bit larger than the Earth’s moon. It is the smallest planet in our solar system and the closest planet to the sun.

It is a terrestrial planet, which means it is an Earth-like planet made up of rocks or metals and has a hard surface. Other planets like Saturn are made of gas.

Like Venus, it has no moons and no rings around it.


Who Discovered Mercury?

No one knows exactly but the Romans named Mercury after their messenger god who was their fastest god and the one they prayed to for success in business.

Related: Why is Mercury not the hottest planet?

Because it is the closest planet to the sun, it looks as if it’s moving quickly from one night to the next and it has a funny way of orbiting that looks like it’s travelling backwards and forwards in the sky.

This is called an elliptical orbit, and is similar in shape to an egg.

egg cup

It takes 88 days for Mercury to orbit the sun and it moves at 31 miles (50 kilometers) per second faster than the other planets.

The Earth rotates every 24 hours and Mercury takes 59 Earth days to rotate. On Mercury, one solar day equals 175.97 Earth days. Wow, that would be one seriously long day!


Temperatures on Mercury

Because it is the closest planet to the sun it was thought to be the hottest planet but this isn’t actually true surprisingly.

It has no way of retaining its heat as it doesn’t have a large atmosphere, so in fact Venus is the hottest planet in our solar system.

During the day Mercury is super-heated by the sun but at night the temperature drops to below freezing.

Temperatures can reach 800 degrees Fahrenheit (430 degrees Celsius) in the day and drop to -290 degrees Fahrenheit (-180 degrees Celsius) at night. Well we won’t be going there then will we?

thermometer invention

Mercury has an inner metallic core about 1,240 miles (2,000 kilometers) wide which is about 80 percent of its radius.

Researchers used radars to study the core in 2007 and found it is partly liquid and has an outer crust about 250 miles (400 kilometers) wide.

The Atmosphere on Mercury

Its atmosphere is made of mostly oxygen (O²), sodium (Nª), potassium (K) and helium (He). Helium is the funny gas that makes you sound like Donald Duck if you suck it from a party balloon. 

It is a dangerous gas and you could die from lack of oxygen if you breathe too much helium in.

helium party balloons

Who has Visited Mercury?

One of the first spacecraft to visit Mercury was Mariner 10 in 1974-5 which took pictures of nearly half the surface.

It looks a bit like the Earth’s moon with a lot of craters from meteoroids and comets crashing into it.

There is a huge crater called the Caloris Basin, about 960 miles (1,550 kilometers) wide, which is the length of more than 16,000 football fields put end to end.

That’s seriously big. This was made by asteroids hitting Mercury a very long time ago.  There are also some very long cliffs and large areas of smooth land, as well as volcanic damage.

volcanic eruption

Radar used in 1991 showed Mercury may have water and ice at the north and south poles, deep inside craters and kept frozen by a permanent shadow.

This is in spite of the high temperatures of the sunlit parts of the planet.

Other missions have flown past Mercury between the years of 2008-2009 to continue taking pictures of the surface before going into orbit in 2011.

water and ice on Mercury

Can we see Mercury from Earth?

Mercury is not easy to see except at dawn and twilight because of its closeness to the sun. It can be seen more easily when it passes across the face of the sun, 13 times each century. 

These transits occur between 7 May and 10 November. So the next transit this century will be on 9 May 2016 and 11 November 2019.


Interesting Facts about Mercury

The famous Hubble Space Telescope can never be used to investigate Mercury as the planet is so close to the sun that the sun’s light could destroy the telescope’s mechanism.

Mercury is obviously getting old as it has wrinkles. As the iron ore of the planet cooled and then contracted it became all wrinkly. How weird.

Scientists have named these wrinkles Lobate Scarps. The scarps can be massive!

Half of Mercury has never been seen, so there’s a whole lot more to discover.


Now finally, this is weird! A year on Mercury is only 88 days long, but a full day as we know is about 176 days, even though the planet takes 58 days to rotate on its axis. That is seriously strange.

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