Facts About Planet Mercury - The Closest Planet To The Sun


Mercury-Facts about the mercury
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. Since 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 and about 40% larger than our Moon. So far only two spacecraft have visited the Mercury from Earth, Mariner 10 in 1973 and MESSENGER in 2004.

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 has a magnetic field which is 1.1% of our earth's field.
  5. The Gravitational force of Mercury is only 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. The model was prepared by keeping the Sun at the centre and orbiting planets. From this model, it turns out that the Sun is the centre of our solar system and all eight planets including earth orbits the Sun. 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.

Since it is so close to the Sun, the solar wind and intense sunlight blow its atmosphere gases constantly. However, 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. This great temperature fluctuation is because Mercury has a thin atmosphere. Despite being the closest planet to the sun, 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. In case of Mercury, the atmosphere is very thin. So, instead of trapping heat, its surface radiates most of the heat back into space.
  • Mercury has a very long tail

Mercury's Sodium tail
Mercury's Sodium tail

Mercury has a bright and yellow-orange comet-like long tail. Its length is estimated about 1.6 million miles or 2.5 million kilometres. Researches have shown that it is made up of evaporated sodium atoms. Previously its length was detected 15 times of the mercury radius, and now it is 100 times more than its radius. 

The sodium atoms are blasted off from the surface by meteors action and intense solar radiation. When the sodium atoms evaporates from the surface then the solar radiation coming from the Sun, pushes back the sodium atoms, creating a long tail of sodium. The sodium atoms takes almost 15 hours to reach its tails from the surface.
  • Mercury's most of the mass in its core

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 crust falls 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.

However, the mantle of Mercury is considerably smaller than our home planet. Mercury's 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. The solidification of its molten causes the surface of Mercury to stretch inwards, reducing its volume. As a result, Since 4.5 years till now, Mercury has been reduced 7 km or 4.4 miles in radius.

The data from Messenger shown various ridges on Mercury's surface. These scrap and ridges are caused due to the contraction of the surface. There are almost 5,934 scarp and elevations ranging from 9 to 900 kilometres or 5 to 560 km long.
  • Mercury surface is similar to our Moon's

Mighty Caloris basin
Mighty Caloris basin

Due to continuous bombardment with meteorites and asteroids, there are many craters on the mercury's floor. They are ranging from 100 meters to 1,300 km in diameter. The craters are named according its length. 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. This crater was formed 3.8 years ago, due to the collision of an asteroid whose diameter was at least 100 meters. When it was discovered by Mariner 10 in 1974, its diameter was calculated to 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.
  • 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 it is the closeat planet to the Sun. But there are some spots where water is found in form of ice. The water ice are deposited in the deep craters on its poles. The axial tilt of Mercury prevents the direct sunlight to reach the surface. Hence, making suitable condition to form ice by keeping the temperature of the deep poles' crater below -171°C or -275° F.

According to some 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 made the 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

There are times when Mercury experiences two sunrises. 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 from where it comes and then rise again.
  • We have visited the Mercury twice and are preparing to visit again

MESSENGER Probe
MESSENGER Probe

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. It made its closest approach to Mercury on March 29, 1974. Flying by two more times over the next year, it mapped approximately 45% of Mercury's surface.

In 2004, NASA again sent another probe named MESSENGER probe to take higher resolution photos of the surface. It orbited around Mercury over 4,000 times between March 2011 and April 2015. On this course, it collected 100,000 images and mapped the entire Mercury's surface. 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 about 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.

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