101 Facts About the Planet Mercury

Although Mercury is the closest planet to the Sun, surprisingly, it’s not the hottest planet in our solar system. It’s also the second densest, and the smallest of the eight planets. It’s so tiny that Mercury is just a little bigger than the Earth’s moon. Want to know more? Keep on reading to learn some fascinating facts about the planet Mercury. 

Fact 1: Mercury is exceptionally close to the Sun orbiting on average only 57.9 million km from the Sun’s surface.

Fact 2: Based on radius and diameter, Mercury, at only 4880 km, is the smallest planet in the Solar System.

Fact 3: It only takes Mercury 87.97 days to complete a full orbit around the Sun.

Fact 4: Mercury is the closest planet to the Sun.

Fact 5: In the 19 century, a French Mathematician called Urbain Le Verrier hypothesized that there was another planet orbiting between the Sun and Mercury. He called the planet Vulcan.

Fact 6: The planet’s proximity to the Sun means that it can only be seen near the western horizon after sunset, or eastern horizon before sunrise, usually in the twilight timezone. 

Fact 7: When seen through a telescope, Mercury, like Venus and the Moon, displays the full range of phases. 

Fact 8: Mercury moves in its inner orbit relative to Earth, which recurs over its synodic period of approximately 116 days. A synodic period is the time it takes for an object in space to return to the same angular position from the Sun as seen from the Earth. Take a look here for a deeper explanation.

Fact 9: Only two robotic spacecrafts have ever visited Mercury.

Fact 10: Mariner 10, a NASA spacecraft, made a flyby in 1974 and 1975.

Fact 11: MESSENGER, another NASA probe, orbited Mercury over 4,000 times in four years before exhausting its fuel and crashing into the planet’s surface on April 30, 2015.

Fact 12: The BepiColombo spacecraft is set to arrive on Mercury at 2025.  

Fact 13: Mercury is one of the five classical planets visible with the naked human eye.

Fact 14: It’s not known exactly when the planet was first discovered, although it was first observed, through telescopes, in the seventeenth century by astronomers Galileo Galilei and Thomas Harriot. 


Fact 15: The Mul.Apin tablets are the earliest known recorded observations of Mercury. The MUL.APIN is a collection of ancient Babylonian stone tablets that record aspects of Babylonian astronomy and astrology.

Fact 16: It takes sunlight 3.2 minutes to travel from the Sun to Mercury. 

Fact 17: When orbiting, Mercury’s closest approach to the Sun, perihelion, is only 46 Million Kilometers. That’s less than 1/3 of Earth’s orbital distance from the Sun which is 149.60 million km.

Fact 18: When orbiting, Mercury’s farthest distance from the Sun, aphelion, is only 69.8 Million Kilometers.

Fact 19: Despite being the smallest of all the 8 planets, Mercury is the second densest planet in the solar system.

Fact 20: Mercury has a density of 5.427 g/cm3, only slightly less than the Earth’s density of 5.515 g/cm3. The high density of the planet is attributed to its large iron-rich core.

Fact 21: Mercury’s core takes up 42% of Mercury’s overall volume.

Fact 22: Compared to all other planets in the solar system, Mercury has the largest core, relative to its overall size.

Fact 23: Mercury’s days are very long. It takes 59 Earth days to complete a full rotation on its axis. That’s compared to 24 hours for Earth to rotate once on its axis.

Fact 24: One Mercury solar day, or one full day-night cycle, is equal to 176 Earth days!

Fact 25: The planet Mercury has the most drastic changes in temperature out of all the planets in the entire solar system with a maximum temperature range, between the hottest and coldest temperature, of 1090℉ (607℃). Mercury has this massive temperature variance because it has no atmosphere to retain and transport heat around the planet.

Fact 26: The hottest temperatures recorded on Mercury reach up to 800℉ (427℃). For comparison, the hottest temperature recorded on Earth was 134.1 °F (56.7 °C)

Fact 27: The coldest temperatures on mercury can plummet to about -290℉ (-180℃). 

Fact 28: Mercury formed about 4.5 billion years ago when the solar system was born.

Fact 29: The small planet began to form when gravity pulled swirling gas and dust together to form planetesimals (small planets). then these planetesimals clumped together to form the larger planets such as Mercury.

Fact 30: Like its fellow terrestrial planets (Mars, Earth, and Venus), Mercury has a central core, a rocky mantle, and a solid crust.

Fact 31: Mercury’s surface is covered with sinuous cliffs called lobate scarp cliffs. These scarps appear to be the surface expression of thrust faults, where the crust is broken along an inclined plane and pushed upward.

Fact 32: Mercury’s interior dramatically shrunk after it formed billions of years ago due to cooling. Because of this, the already solid crust started to collapse in on itself creating the planet-wide lobate scrap cliffs. They are, in effect, wrinkles on the surface.

Fact 33: Mercury looks like the twin of our Moon. Both celestial bodies have many impact craters, but on Mercury, long, jagged cliffs split the crust.

Fact 34: In real light, the majority of Mercury’s surface appears to be a greyish-brown color to the human eye. 

Fact 35: Mercury’s extreme temperatures, and lack of an atmosphere, make it impossible for life to exist on the planet.

Fact 36: There are several science-fiction TV shows about the planet Mercury. Recurring themes include the dangers of being exposed to solar radiation and the possibility of escaping excessive radiation by staying within the planet’s slow-moving terminator. Some of these include “Kinvig” (1981) and “Collision Earth” (2011).

Fact 37: In the 2001 animated TV show “Invader Zim”, Mercury was turned into a giant spaceship created by an extinct Martian species. In the episode “Battle of the Planets”, Zim (piloting Mars, also made into a spaceship) and Dib (piloting Mercury) battle each other while flying through the solar system.

Fact 38: Mercury only has 38% of the Earth’s surface gravity.

Fact 39: Because of its low surface gravity Mercury has no atmosphere, no moons, and no ring systems.

Fact 40: Venus and Mercury are the only two planets that don’t have a single natural moon orbiting them either. 

Fact 41: Mercury is the most cratered planet in the solar system. Mercury lacks liquid water on its surface that would erode impact craters over time. It also lacks an atmosphere, which on planets like the Earth and Venus, an atmosphere could disintegrate meteoroids before they could impact the surface.

Fact 42: Measuring 1,550 km across, the Caloris Basin is the largest impact crater on Mercury. 

Fact 43: The Calorie Impact Basin was discovered in 1974 by the Mariner 10 probe.


Fact 44: Most Mercurian craters are named after famous writers and artists. 

Fact 45: Mercury is named after the Roman messenger god Mercury. 

Fact 46: The Romans knew of seven bright objects in the sky: the Sun, the Moon, and the five bright planets. They named them after their most important gods. Because Mercury was the fastest planet as it moved around the Sun, it was named after the Roman messenger god Mercury because of their speed.

Fact 47: Mercury has been geologically inactive for billions of years. The thousands of perfectly preserved impact craters are evidence of this fact.

Fact 48: With a tilt of just 0.03 degrees, Mercury’s axis has the smallest axial tilt of any of the Solar System’s planets. For comparison, Earth axial tilt is 23.5 degrees.

Fact 49: Mercury’s orbital eccentricity, how far from a perfect circle an orbit is, is the largest of all known planets in the Solar System. The difference between Mercury’s closest and farthest approach from the sun is nearly 51.7%.

Fact 50: at 47.362 km/s Mercury has the fastest orbital speed of all the planets in the solar system. to give you an idea of how quick this is, you could travel from London to New York, a distance of 5,567 km, in just 117 seconds! That’s less than two minutes.

Fact 51: Mercury’s diameter is only 4880 km. This makes it about 50% larger than the Moon which is itself 3,474.2 km in diameter.

Fact 52: The surface area of Mercury is 7.48×107 km2. Written out in full that number would be 74,800,000 km2. For comparison, Africa’s land area is about 30.37 million km².

Fact 53: Mercury’s Volume is about 6.083×1010 km3 . Again, written out in full that number is 60,830,000,000. Or, 60.8 billion. That equals about 1/20th of Earth’s volume.

Fact 54: Mercury has a mass of roughly 3.3011×1023 kg. A huge number, that when written out, looks something like this: 330,110,000,000,000,000,000,000 kg. But even though that’s a massive number, it still only equals 1/20th of Earth’s mass.

Fact 55: Mercury’s escape velocity is 4.25 km/s. In comparison, Earth’s escape velocity is 11.186 km/s.

Fact 56: The apparent magnitude of mercury varies between −2.48 to +7.25. The dimmest apparent magnitude the naked eye can see +6.5. So Mercury can be easily spotted by the naked eye for most of its orbit.

Fact 57: Mercury has a triple-core configuration. The outer core is made of solid Iron-sulfide. The middle core layer is liquid, likely Iron-Sulfide and Nickel. Then there is the inner core, a solid sphere of Iron and Nickel.

Fact 58: Mercury is also smaller than the largest natural satellites, or moons, in the Solar System: Ganymede orbiting Jupiter and Titan orbiting Saturn.

Fact 59: Mercury is made of roughly 30% silicate material, such as rock, and 70% metallic material, such as Iron and Nickel.

Fact 60: Mercury’s core accounts for over 55% of the total planet’s volume. For comparison, Earth’s core only makes up 17% of Earth’s volume.

Fact 61: Mercury’s mantle is estimated to be between 500 and 700 km thick.

Fact 62: Mercury outer crust is thought to be no more than 35 km thick.

Fact 63: Data indicates that Mercury’s core has a higher iron content than any other planet in the Solar System.

Fact 64: When Mercury first formed, it would have likely had to endure temperatures from our early sun of more than 10,000°C or 18,000.1°F. This would have meant that Mercury would have had an atmosphere of vaporized rock.

Fact 65: The Caloris Basin was once filled with Lava. It would have resembled a giant molten rock filled lake that stretched for 1000s of kilometers.

Fact 66: Images taken by the Mercury MESSENGER probe have provided evidence to suggest that volcanic pyroclastic flows once regularly flowed over the surface of Mercury.

Fact 67: Observations strongly suggest that frozen water exists on Mercury in deep craters. The bottom of craters at both the south and north poles are never exposed to direct sunlight leading to constant very low temperatures.

Fact 68: The total amount of Ice mercury’s craters hold is thought to be in the region of 10,000,000,000,000 kg. Or 10 trillion kg of ice. That number may sound like a lot but it’s actually thousands of times less than the amount of ice held in Antarctica on Earth.

Fact 69: Though it commonly accepted Mercury doesn’t have an atmosphere, it does actually have a very thin exosphere. The surface pressure, of less than 0.005 picobars, is lower than many vacuum chambers on Earth.


Fact 70: Mercury’s extremely thin exosphere is not stable. Sometimes it disappears for months, lost to the solar winds, only for it to be replenished again from atoms leaking out of the crust.

Fact 71: The Mercury MESSENGER Probe’s principal investigator was Sean Solomon, a Professor of Earth and Planetary Science.

Fact 72: Mercury has a global magnetic field that about 1.1% the strength of Earth’s magnetic field.

Fact 73: Mercury’s magnetic field is dipolar and is nearly perfectly aligned with the planet’s axis of rotation.

Fact 74: Mercury’s rotating liquid outer core gives rise to a phenomenon known as the dynamo effect. This creates Mercury’s magnetic field.

Fact 75: Mercury’s liquid outer core is kept in a liquid state by the heat generated from the compression and decompression of the planet as it orbits close then far away from the Sun. To get an idea of how this effect works, grab your thumb with the other hand and squeeze your thumb with your other hand then relax. Repeat this 10 times and both your thumb and your hand will warm up. This heat is generated from compression and decompression.

Fact 76: Mercury’s magnetic field is strong enough to create a magnetosphere around the planet that helps to deflect some of the incoming solar wind.

Fact 77: The Mercury MESSENGER discovered magnetic tornadoes in the magnetic field that surrounds the planet. These twisted bundles of magnetic fields can be up to 800 km wide and funnel down from outer space.

Fact 78: Compared to the ecliptic plane, Mercury’s orbit is inclined by 7 degrees. More than any other planet.

Fact 79: Along with other planets and some stars, Mercury can be easily observed during a total solar eclipse.

Fact 80: Due to safety procedures that prevent the Hubble Space Telescope from pointing too close to the Sun, Mercury can’t be observed by it as the sunlight would instantly burn out the delicate instruments.

Fact 81: Mercury and Venus occult, pass in front of each other, every two to three hundred years. The only time this has ever been observed was on May 28, 1737, by John Bevis at the Royal Greenwich Observatory in London, UK.

Fact 82: Mercury has been studied far less than the other planets because it is so hard to observe.

Fact 83: In 1800, Johann Schröter, a German astronomer, claiming he had observed 20-kilometer-high mountains on Mercury’s surface.

Fact 84: It was originally thought that Mercury was tidally locked to the Sun. This means the Mercury orbit at the same speed that it rotates on its axis, so it always shows the Sun the same face. The same way the moon always shows the same face to Earth. However, this was later proved to be wrong.

Fact 85: In June 1962, Vladimir Kotelnikov and his team at the Institute of Radio-engineering and Electronics in the USSR became the first to bounce a radar signal off Mercury.

Fact 86: Sending probes to Mercury is extremely difficult. This is because Mercury’s orbital velocity is 18 km/s faster than Earth’s. This means that when a Probe leaves Earth, it somehow has to gain 18 km/s to “catch up” with Mercury. Building up this speed is very difficult just with rockets. So a complex collection of slingshot maneuvers around other planets are used to give Mercury bound probes the speed boost they need to slot into orbit around Mercury.

Fact 87: A probe traveling to Mercury requires more rocket fuel than the fuel needed to escape the Solar System completely.

Fact 88: Mariner 10 used the gravity of Venus to gravitationally slingshot into Mercury’s path.


Fact 89: Mariner 10, the first mercury probe, was the first NASA probe to visit multiple planets in a single mission.

Fact 90: Mariner 10 was the first probe to take close-up images of Mercury’s surface.

Fact 91: Mariner 10 only took photos of one face of Mercury as only one side of the planet was lit for each of Mariner 10’s fly-bys.

Fact 92: Only around 45% of Mercury’s surface was mapped by Mariner 10.

Fact 93: Mariner 10 made 3 close approaches to Mercury coming within 327 km of its surface.

Fact 94: On March 24, 1975, Mariner 10 ran out of fuel. That was just eight days after its final close approach to the planet.

Fact 95: After Mariner 10 ran out of fuel, NASA Instructed the probe to shut itself down. The probe still lives today in orbit around the Sun and makes a close approach to Mercury every 12 or so weeks.

Fact 96: The Second Probe to visit Mercury was NASA’s MESSENGER probe. MESSENGER is an acronym for MErcury Surface, Space ENvironment, GEochemistry, and Ranging.

Fact 97: Like Mariner 10 Before it, the MESSENGER probe also used a slingshot maneuver around venus to slot into Mercury orbit. However, it also got a second slingshot by revisiting Earth.

Fact 98: MESSENGER’s first fly-by of Mercury was on January 14, 2008.

Fact 99: On March 18, 2011, MESSENGER final entered an elliptical orbit around the planet after multiple fly-bys.


Fact 100: MESSENGER’s main mission was to examine the following:

  • The nature of Mercury’s magnetic field
  • What causes the planet’s high density
  • Where does Mercury’s tenuous atmosphere come from
  • What is the planet’s geological history
  • Was there/is there ice at its poles
  • What is the structure of its core

Fact 101: On April 30, 2015, after running out of fuel, MESSENGER‘s final act was to crash into Mercury’s surface. It gouged out a crater over 16 m (52 ft) in diameter.


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