Facts about Mercury - Interesting Mercury Facts you should know

Mercury-Facts about the mercury

Mercury is the smallest of eight planets in our solar system. It completes its orbit around the sun in 87.97 days which makes it the fastest orbiting planet. Because it is the fastest planet, its name was placed on Roman God of Commerce, travel and thievery. With a diameter of 4,879.4 km, Mercury is almost the size of the continental United States, but it is 40% larger than our Moon. So far only two spacecraft have visited the Mercury from Earth, Mariner 10 in 1973 and MESSENGER in 2004. Check out these weird and interesting Facts about the Mercury.

Facts about Mercury

Planet Profile

Name   Mercury
Known Satellite   0
Distance from Sun (avg)   57.91 million km
Radius   2,439.7 km
Volume   6.083 × 1010 km3
Mass   3.285 × 1023 kg
Surface area   74.8 million km2
Gravity   3.7 m/s2
Max Temperature     + 840 °F (+ 449°C)
Min Temperature     - 275 °F (- 170°C)  
Length of day   58.646 Earth Days
Length of year   88 Earth years
Astronomical symbol   

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Quick Facts About Mercury

  1. From the mid-1800s to early 1900s, it was believed that a planet named "Vulcan" lies between the Sun and Mercury. But Einstein’s General Theory of Relativity Proved it wrong.
  2. Due to Mercury’s rapid orbit, Ancient Greeks thought that Mercury was two stars and gave the planet two names - Apollo, when it was visible in the morning and Hermes, at night.
  3. Between 2000 and 1001 BCE, the Babylonians named this planet, Nabu. 
  4. Mercury's has a magnetic field which is 1.1% of our earth field.
  5. The Gravitational force of Mercury is 38% of the earth gravity.
  6. If you weight 68 kg on Earth, you would weigh only 25.7 kg on Mercury.
  7. Jupiter's moon - Ganymede and Saturn's moon - Titan are more massive than Mercury.
  8. Despite its smallest size, Mercury is the second densest planet in our solar system (second only to our Earth), thanks to its large metallic core.
  9. Mercury is so close to the Sun that Hubble can't look at it. The solar light would overwhelm Hubble and damage its optics and electronics.
  10. In spite of rotating in 58 earth days on its axis, the time from sunrise to next sunrise is 176 days.
  11. Only Mercury's crust has no tectonic plate.

Detailed Facts about Mercury 

  • Nobody knows who discovered Mercury and when

Nicolaus Copernicus's Solar Model
Nicolaus Copernicus's Solar Model

It is impossible to pinpoint who has discovered it and when. Since Mercury is one of the 5 classical planets that can be seen with the naked eye. The ancient people know that these 5 are different from other stars. The five worlds are Mercury, Venus, Mars, Jupiter and Saturn.

The astronomers did not know that Mercury was a Planet until Nicolaus Copernicus modelled a solar system in 1543, which was prepared by keeping the Sun at the centre. From this, it turns out that the Sun is the centre of our solar system, not the Earth. This discovery was confirmed when Galileo Galilei and Thomas Harriot observed the planets through his telescope, which matched the model.

  • Mercury has a very thin atmosphere which keeps replenishing

Mercury’s small size and a weak gravitational pull make it nearly impossible to maintain a normal atmosphere. But Mercury has a very thin atmosphere, even more tenuous than Mars' atmosphere.  Scientists call it exosphere. It is made up of hydrogen, helium, oxygen, sodium, potassium, magnesium and calcium.

Because it is too close to the Sun, the solar wind and high sunlight blow its atmosphere gases constantly. But also, its atmosphere keeps continuously replenished too. Some of the hydrogen and helium gas comes from the same solar winds. Radioactive decay and Micrometeorites are other sources of the rest of the gases. That's why Mercury still has a thin atmosphere.

  • Mercury faces extreme temperature swing

Mercury passing in front of Sun.
Mercury is passing in front of the Sun.

During the daytime, Mercury is boiling and sizzling, with the temperature reaching over 449°C or 840 °F, but as soon as the sun goes down, the temperature drops down to 170°C or - 275 ° F. Despite being the closest planet to the sun, even Venus is hotter than Mercury with max temperature 870 °F or 465°C.

This is because Venus has a thick atmosphere and mainly contains carbon dioxide, which is a significant greenhouse gas. Thus its atmosphere traps heat from the sun and prevents it from escaping into space. Since Mercury has a very thin atmosphere, so its surface radiates most of the heat back into space.

  • Mercury has a very long tail

Mercury's Sodium tail
Mercury's Sodium tail

This bright yellow-orange like a comet tail is 1.6 million miles long and is made up of sodium. Since the gravitation of the Mercury is too week to hold its thin atmosphere. So when sodium atoms are evaporated from its surface then the solar radiation, which is coming from the Sun pushes back the sodium atoms, creating a long tail of sodium.

The time taken by the sodium atoms to reach its tails from its surface is almost 15 hours. Previously it is detected 15 times of the mercury radius, and now it is 100 times more than its radius.

  • Mercury’s has a huge core which occupies 85% of the planet's radius.

Internal Structure of Mercury
Internal Structure of Mercury

Mercury core's radius is about 1,100 to 1,200 mile or 1,800 to 1,900 km which occupies 85 per cent of the planet radius. While Earth's core holds only 17 per cent of the planet volume. Even then its core has more iron than other planets in our solar system.

Mercury’s most exterior layer is crust, falling somewhere within a thickness of 60 to 185 miles or 100 to 300 kilometres. Making Earth’s puny 20 to 30 mile or 30 to 50-kilometre crust seem flimsy.

Beneath that, though, the mantle of Mercury is considerably smaller than our home planet. The mantle is 310-430 miles or 500-600 kilometres thick compared to Earth’s 1,802-mile or 2,900-kilometer thickness.

  • The smallest Planet Mercury is shrinking

Wrinkle ridges on Mercury's surface
Wrinkle ridges on Mercury's surface

Mercury has a partially molten core that is gradually cooling down over time. Since the molten core is cooling and is turning into solid, thus it causes the surface of Mercury to stretch inwards, reducing its volume. As a result, from 4.5 years till now, mercury has been reduced to 7 km or 4.4 miles in radius.

The evidence is the data from MESSENGER shows that Mercury's surface contracted. Since this contraction causes large scarp and ridges on the surface. There are almost 5,934 scarp and elevations ranging from 9 to 900 kilometres or 5 to 560 km long.

  • Mercury surface has many craters which make it similar to our Moon

Mighty Caloris basin
Mighty Caloris basin

Due to continuous bombardment with meteorites and asteroids, there are many craters. They are ranging from 100 meters to 1,300 km in diameter. Any crater is larger than 250m then it is known as a basin. There are 397 named craters and most craters have been named after famous artists, writers, artists and composers.

The most massive crater on the surface of Mercury is the Caloris Basin. When it was discovered by Mariner 10 in 1974, its diameter is about 1,300 km or 810 mi. But the images taken by the MESSENGER probe shows that the crater increased to 1,540 km or 960 miles in diameter. This crater was formed 3.8 years ago, due to the collision of an asteroid whose diameter is at least 100 meters.

  • There is ice on poles of the Mercury

Ice (yellow areas) on Mercury's North pole

It sounds unbelievable when you find out that there is water ice on the Mercury, even though this is so close to the Sun. Since the axis of the Mercury is slightly tilted, hence the direct sunlight never reaches the floors of deep craters on its poles. It keeps the temperature of the deep crater below -171° C or -275° F.

According to researchers, water enriched comets and asteroids have brought water on its craters. A second idea is that the hydrogen with oxygen is supplied by the solar wind on the surface that make water.

  • Mercury's orbit is the most eccentric in our solar system

After 1 orbit, mercury has rotated 1.5 times and after completing 2 orbits the same side is again illuminated
After one orbit, Mercury has rotated 1.5 times, and after completing two orbits, the same side is again illuminates
 © Wikimedia

Now the Pluto is no longer a planet. The Mercury takes the record of the most eccentric orbit in the solar system. Its orbit is ranging from 46 million km or 28.58 million mi (perihelion) to 70 million km or 43.49 million mi (aphelion). At 170,500 km/h or 105,945 mph orbital velocity, it takes 87.96 earth days to complete its one orbit and 58.65 earth days to rotate on its axis.

Though it was initially believed that Mercury had a 1:1 ratio of rotations per orbit, Einstein’s General Theory of Relativity showed a different light. Mercury is now known to have a spin-orbit resonance or direct correlation between orbital and rotational periods. It experiences three rotations per 2 orbits around the Sun.

  • There are double Sunrises and noon on Mercury

As Mercury comes near the Sun (perihelion), the Sun becomes three times bigger than as viewed from the earth and its speed increases. As it goes away from the sun (aphelion), the sun becomes almost half in size and its speed decreases. This causes the Sun to rise, and when it comes in the overhead position, it pauses for some time, then it temporarily moves backwards, and again continue its motion towards sunset.

If you are in that position where the sunrise occurs in the time of perihelion, then you will see the Sun to rise, slows, stop, hides almost where it comes and then rise again..

  • We have visited the Mercury twice and are preparing to visit again


Mercury’s proximity to the sun is direct reasons why only two missions were performed. On November 3, 1973, Mariner 10 launches, for the first time to visit Mercury. On March 29, 1974, it made its closest approach to Mercury. Flying by two more times over the next year, it mapped approximately 45% of Mercury's surface.

In 2004, NASA sent MESSENGER probe to take higher resolution photos of the surface. It orbited around Mercury over 4,000 times between March 2011 and April 2015. It collected 100,000 images and mapped the entire Mercury. In 2025, the ESA and JAXA will be launching BepiColombo to continue monitoring the tiniest planet. 

  • Here is the most massive Man-made Crater

MESSENGER impact site on Mercury
MESSENGER impact site on Mercury

It looks as if humans can't resist but dig holes even in space! On April 2015, the 10 foot wide NASA’s MESSENGER probe exhausted its supply of fuel and crashed on to the surface of Mercury at the speed of over 8,500 mph or 13,500 km/h. The crash resulted in a massive crater over 50 ft or 16 m wide, the size of a basketball court. It is the biggest human-made craters ever created in the universe.

Besides severely injuring the surface of Mercury, NASA's MESSENGER probe successfully mapped the entire surface of the planet. It had been orbiting Mercury since 2011 and recorded several gorgeous images.

How about these Mercury Facts?

Those are the interesting facts about Mercury. How about you?  Want to know more information and facts about Mercury? Check out these links:

  1. https://en.m.wikipedia.org/wiki/Mercury_(planet)
  2. https://solarsystem.nasa.gov/planets/mercury/overview/
  3. https://solarsystem.nasa.gov/planets/mercury/in-depth/

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