Mercury Facts

Mercury is the smallest planet in the Solar system and as well as the closest to the Sun. Since, it’s nearest to the Sun, it takes only 87.97 days to revolve around the Sun. It’s named after the Roman God ‘Mercury’. It is visible to naked eyes from Earth.

Mercury Profile

Interesting Mercury Facts

  • Mercury is the closest to the sun out of all the planets in the solar system i.e. 57.91 million kilometers away.
  • It takes 87.97 Earth days to complete one revolution and 59 Earth days to complete a rotation.
  • Mercury is the innermost and smallest planet in the solar system.
  • Along with Venus, Earth, and Mars, Mercury is one of the terrestrial planets in the Solar System.
  • Mercury has no moons i.e. no natural satellites making it one of the only two planets with Venus to have no moons. Only other planet with no moon is Venus.
  • Mercury travels the fastest of all the planets traveling at the speed of 1,80,000 km/hr.
  • It is the second densest planet in the Solar System.
  • As it is closest to the sun, it is the least explored planet of the Solar System.
  • There are no rings around Mercury.
  • Mercury may have had volcanoes in the past.
  • The Sunrays hitting mercury are seven times stronger than the Sun rays hitting the Earth.
  • It spins anticlockwise i.e. from west to east.
  • Mercury is a naked eye planet. Some of the civilizations to observe and mention it were Sumerians and Assyrians. Copernicus also observed this planet in the 16th Century. This planet was first observed through a telescope by Galileo Galilei in the 17th Century.


It is believed that Mercury was formed more than 4.5 billion years ago as a result of the combination of gas and dust due to gravity. It is the closest to the sun out of all the planets and therefore has the shortest period of revolution. Hence, it has been named after the swift-footed Roman messenger of God.

It is believed that the Sumerians could have known about it for 5000 years and have associated it with the God of writing. Interestingly, its time of discovery is not known as it is one of the five naked planets which anyone can see. However, it was first observed from a telescope by Galileo Galilei and Thomas Harriot in the seventeenth century. Pierre Gassendi became the first man to observe a transit of the planet Mercury across the Sun in 1631.

Mercury has been visited by two spacecrafts, Mariner 10 (1974-1975) and MESSENGER (2004).


Mercury is known to be of a light-grey color with a big star-shaped crater towards the bottom of the globe. This star-shaped crater is known as Debussy. Crater rays are formed when an asteroid or a comet strikes the surface of a planet. A huge hole is created on the surface because of the tremendous amount of energy released in this process. Mercury is one of the five classical planets visible to the naked eye.

Standing on Mercury’s surface at its closest approach to the Sun, our star i.e. if a person was standing on the surface of Mercury, the sun would appear three times bigger than how it appears on the Earth.

Ancient people believed that there existed two distinct planets, instead of just one which was Mercury. This was because Mercury could be seen twice a day; once in the morning and the next time in the evening. Due to this, Greeks named the planet Apollo in the morning while they named it Hermes in the evening sky. In reality, Mercury orbits the sun very fast. This is why it’s seen twice a day.

Observers on Earth can watch Mercury pass across the face of the Sun 13 times every hundred years. This is called a transit. The next transit will take place on November 13, 2032.


Mercury is 57.91 million kilometers away from the sun. It has a radius of 2440 km and an equatorial circumference of 15,329 km. It has a surface temperature of -180°C to 440°C. In fact, Mercury has the largest range of surface temperatures than any other planet.

Its orbital speed is about 180,000 km/ h or 47 km/s which is 60% faster than the Earth’s speed. It is slightly larger than the Earth’s Moon and about 2.6 times smaller than the Earth. It has a surface area of 7.48×107 km2.  It weighs about 3.30 x 1023 kg. Mercury’s axis has the smallest tilt of all the other planets which is about 1/30°.


It is a rocky planet and is the smallest in the solar system. In 2012, NASA’s Messenger discovered water ice near it’s the North Pole where regions don’t receive the light of the sun. Scientists believe that meteorites and comets could have delivered ice to those areas, or water vapor from Mercury’s innards could have seeped out and frozen.

Like the moon, Mercury consists of several craters and rocks on its surface which are caused due to impacts of space rocks. In fact, it has more craters than any other planet of the solar system. Caloris Basin is the largest of these with a diameter of almost 1,550 km. Plains have also been found between these craters.

It is believed that dried lava could be covering most of the surface of mercury. Northern plains of the planet appear to be smooth because lava may have poured over the surface and smoothened. Even though volcanic activity is not seen on the surface of mercury anymore, many think it could be a good explanation for the appearance of the planet today.


Mercury’s core has iron content higher than that of any other planet in the Solar System and this has been explained by many proposed theories. The most widely accepted of which is that Mercury had a metal–silicate ratio similar to common chondrite meteorites, originally, and was thought to be typical of a mass approximately 2.25 times its current mass.

Mercury consists of around 70% metallic and the remaining 30% of silicate material. It is the second densest planet in the solar system after Earth. It has a density of 5.427 g/cm3 which is slightly less than the density of the Earth which is 5.515 g/cm3. This is due to the abundance of iron in its core.

Magnetic field

Mercury has a significant magnetic field. The field, however, is very weak, just about 1% of that of the Earth. Just like the earth, this field is dipolar. Scientists believe that this magnetic field may be caused by the dynamo effect.

This magnetic field sometimes interacts with the solar winds to form tornados. These tornados funnel solar wind plasma to the surface of the planet. It is also believed that about a billion years ago, Mercury had a strong magnetic field, almost as strong as that of the Earth.

Orbit & Rotation

As the planet rotates very slowly, days on Mercury are quite long. One day on Mercury is equal to 59 days on planet earth. However, the speed of revolution is very small because mercury is the closest to the sun and hence has the smallest orbit.

One year on Mercury lasts for 88 earth days. Mercury’s orbit is elongated, and its rotation is slow. This results in Mercury having an unusual sunrise. In some places on the planet, the sun appears to rise briefly before setting and rising again. The exact reverse happens at the time of the setting.

One day on Mercury (sunrise to sunrise) is longer than one year on Mercury (one orbit around the Sun).

The planet’s spin around its axis is almost vertical. Hence, its poles don’t get enough sunlight. The axis of rotation of the planet is tilted just 2°. That means it spins nearly perfectly upright without experiencing seasonal variations like most planets do.


Mercury has a very thin or almost no atmosphere. The planet’s atmosphere is so thin that scientists also call it an exosphere. The atmosphere consists mostly of hydrogen, helium, and oxygen with small amounts of sodium, potassium, calcium, and magnesium. Atmospheric pressure is about one trillionth of that of the earth i.e. approximately one nano pascal or 10-14 bar.

As it is very small in size, it has a very weak force of gravity (38% the gravity of Earth) which is too weak to hold on to its atmosphere, as a result, this causes it to be blown away by solar winds.


Mercury has no moons. This is because of its proximity to the sun as the presence of such a huge body with a strong gravitational pull is likely to cause the body to pull the moon out of the orbit of its parent planet.

Mercury moves with a tail behind it which is similar to that of a comet. This is a recent discovery. This tail is made up of sodium atoms, which are influenced by the intense pressure of the Sun’s radiation.


Two spacecrafts have visited Mercury namely Mariner 10 and MESSENGER, both by NASA.

  1. Mariner 10: NASA’s Mariner 10 was the first spacecraft to visit Mercury. Its main objective was to observe and record Mercury’s environment, atmosphere surface and body characteristics. It was able to take pictures of less than half of the surface of Mercury. It flew by Mercury three times.
  2. MESSENGER: MESSENGER stands for Mercury Surface, Space Environment, Geochemistry, and Ranging. It was launched aboard a Delta II rocket in August 2004 and orbited Mercury from 2011 to 2015. Its main objective was to study characteristics like the surface, body, magnetic field, etc. Scientists have used the images sent by MESSENGER to create the first-ever complete map of Mercury’s surface. The mission came to an end in 2014 when MESSENGER crashed onto the surface of Mercury after running out of propellant.
Mariner 10 was an USA robotic space probe launched by NASA on November 3, 1973, to fly by the planets Mercury and Venus.
MESSENGER: MESSENGER was a NASA robotic spacecraft that orbited the planet Mercury between 2011 and 2015, studying Mercury's chemical composition, geology, and magnetic field.

The European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA) have planned a joint mission called BepiColombo, proposed to be launched in 2018 and expected to reach mercury in December 2025. This will be the first expedition on Mercury for both space agencies.

Shrinking Mercury

The planet is made up of a single continental plate covering the entire planet. Mercury has a large iron core (4040 km) and very thin skin with only 420 km of the mantle and crust. This means that it does not have an internal source to renew heat and because of this, the iron in its core is cooling.

As a result, the surface of the planet is contracting. Hence, it is shrinking in volume. This phenomenon has been taking place for billions of years.

Potential for Life in Mercury

Its proximity towards the sun and the radiations received by it make the conditions too extreme for the presence of life. As of now, no evidence of life has been found on Mercury.

Mercury in Pop Culture

A number of science-fiction writers have been inspired by the planet Mercury and have included it in their stories. Some of these writers include Isaac Asimov, C. S. Lewis, Ray Bradbury, Arthur C. Clarke, and H. P. Lovecraft.

Mercury has also found a place in the film and television industry. In ‘Invader Zim’, an animated television show, the extinct Martians turn Mercury into a prototype giant spaceship.

In the 2007 film ‘Sunshine’ a spacecraft called the Icarus II goes into orbit around Mercury to meet Icarus I, another spacecraft.


  1. 5 Billion BC: Mercury is formed.
  2. 5000 BC: Earliest evidence of knowledge about Mercury.
  3. 1631: Observation of Mercury by Galileo Galilei and Thomas Harriot with the help of their newly invented telescope.
  4. 1631: Pierre Gassendi uses a telescope to watch from Earth as Mercury crosses the face of the Sun.
  5. 1965: Astronomers using radar find that the planet rotates three times for every two orbits, contradictory to the ancient belief that the same side of Mercury always faces the sun.
  6. 1971: Boing receives a contract for Mariner 10 for the exploration of Mercury.
  7. 1974-1975: NASA’s Mariner 10 is launched and sends ten photographs of less than half of the surface of planet Mercury.
  8. 1991: Scientists find signs of ice locked in permanently shadowed areas of craters in Mercury’s Polar Regions using Earth-based radar.
  9. 1993: Transit of Mercury.
  10. 2004: NASA’s MESSENGER (Mercury Surface, Space Environment, Geochemistry, and Ranging) is launched.
  11. 2008-2009: MESSENGER observes Mercury during three flybys.
  12. 2011: MESSENGER begins its orbital mission at Mercury, yielding a significant number of quality images, compositional data, and scientific discoveries.
  13. 2015: MESSENGER crashes into the surface of Mercury after expending all its propellant, ending its mission at its expected time.
  14. 2018: BepiColombo is proposed to be launched.


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