Cool Facts About Mercury

tl;dr: check out our 10 Facts About Mercury Infographic

Everybody loves Mercury, it’s one of the planets we’ve known very little about for a very long time, yet held it near and dear to our hearts. Due to the lack of information about Mercury, we’ve relied on our imaginations and speculations, for a long time.

Today, we can imagine Mercury in a much different sense, based on facts, rather than myths. After the fly by in the 1970’s by the Mariner 10 spacecraft and the arrival of NASA’s Messenger spacecraft back in 2008 – we know a lot more today than we once knew about Mercury.



“PIA19450-PlanetMercury-CalorisBasin-20150501” by NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington – Licensed under Public Domain via Commons –


In this post, we’re going to learn about some very Cool Facts About Mercury and see why people love this very enchanting and dangerous place. But first, a little about Mercury and what makes it, well, Mercury.

Mercury’s Planetary Profile:

  • Planetary Mass: 330,104,000,000,000 billion kg (0.055 x Earth)
  • Planetary Diameter: 3,032 miles
  • Planetary Radius: 1,516 miles
  • Planetary Circumference: 9,525.1 miles
  • Planetary Moons: None
  • Average Solar Orbital Distance: 36,800,000 miles
  • Solar Orbit Period: 87.97 Earth days
  • Planetary Surface Temperature: -279.4 to 800.6 degrees Fahrenheit
  • First Record of Mercury: ~3,000 BC
  • Recorded By: Sumerians
  • Distance From Earth: 48 – 137 Million Miles

Cool Facts About Mercury – Fact #1:

Mercury is the smallest of all the 8 planets in our Solar System.

Now this wasn’t always the case, but after the announcement by the International Astronomical Union (IAU) on September 13, 2006, Pluto was classified as a dwarf planet.



“Mercury, Earth size comparison” by NASAMercury image: NASA / APL (from MESSENGER) – The Earth seen from Apollo 17.jpgMercury Globe-MESSENGER mosaic centered at 0degN-0degE.jpg. Licensed under Public Domain via Commons –


While this didn’t change the physical size of Pluto or Mercury, classifying Pluto as a dwarf planet enabled Mercury to take the title as the smallest (regular) planet in our Solar System. Interested in 10 awesome facts about Pluto?

Cool Facts About Mercury – Fact #2:

One day on Mercury is equal to 176 Earth days.

Mercury is basically locked (tidally) to the Sun and over the millions and millions and billions of years rotating around the Sun, it has slowed its rotation of the planet to match its solar orbit around the Sun.



“Mercury transit 1” by I, Brocken Inaglory. Licensed under CC BY-SA 3.0 via Commons –


In the picture above, you can see Mercury’s Transit. Mercury is the tiny little black dot in the lower right quadrant. Don’t be fooled by the larger black dot on the left center side of the Sun, that’s a sunspot. For more information about how Astronomers use the Transit Method to detect planets, check out this article and video.

Cool Facts About Mercury – Fact #3:

Mercury is the second densest planet.

Second only to yours truly, the Earth. If you were to scoop up a cubic centimeter of material on Mercury, it would weight 5.427 grams. If you were to do the same thing on Earth, it would weigh 5.515 grams. Pretty darn similar. Imagine the density of a gas giant planet like Saturn, with 0.687 grams per cubic centimeter.

A cubic centimeter is roughly the size of a sugar cube.

A U.S. 5¢ Nickel weighs 1 gram.

Cool Facts About Mercury – Fact #4:

Mercury is the second hottest planet.

Many would think that because Mercury is the closest planet to the Sun that it would be the hottest. However, even though Venus is further from the Sun than Mercury, the planet Venus actually has higher temperatures than Mercury.

The reason Mercury has lower surface temperatures than Venus is largely because Mercury has no atmosphere to trap in the heat, like Venus does.

Ok, you’re probably rolling your eyes thinking to yourself, “umm… hello? Mercury does have an atmosphere. What’s wrong with you?”. Well, you’re right, sort of. So let’s check that out now in the next cool fact about Mercury.

Cool Facts About Mercury – Fact #5:

Mercury has no atmosphere and Mercury kind of has an atmosphere.

So… how can you not have something, but kind of have something? I don’t know, but Mercury pulled it off, apparently Mercury is able to have its cake and eat it, too. So put that down as another cool fact about mercury in the appendix.

Mercury’s gravity is only 38% of what the gravity is on Earth. Because of this, there isn’t enough gravity for what is needed to create and retain an atmosphere.



“PIA19285-Mercury-GravityAnomalies-Messenger-20150415” by NASA/Goddard Space Flight Center Science Visualization Studio/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington – Licensed under Public Domain via Commons –


The atmosphere which does get produced is basically blown away by solar winds. Even though the gases on Mercury are constantly and annoyingly being blown away by solar winds, they’re also constantly being replenished.

So basically, Mercury doesn’t have an atmosphere, as we’d define it here on Earth, but it does have what’s known as an exosphere, which is what the Earth’s Moon has.

Detection of sodium, magnesium and calcium have been found in Mercury’s exosphere. The current theory is that these elements experience changes to their levels of concentration based on the levels of solar radiation Mercury experiences.

The solar radiation changes based on Mercury’s distance to the Sun in its very elliptical orbit. This leads us to our next cool fact about Mercury; its awesome orbit.

Cool Facts About Mercury – Fact #6:

Mercury has a very elliptical orbit, versus a circular orbit.

Mercury moves around the Sun in a very elliptical shape, which is pretty interesting. Think about that like this, even though it takes Mercury roughly 88 Earth days to make a full rotation around the Sun, from the vantage point on Earth – Mercury appears to move around the Sun in a full rotation every 116 Earth days.

The reason Mercury appears to have a longer orbit than it actually does it due to its orbital eccentricity. Mercury is about 1.5 times further away from the Sun at the aphelion of Mercury’s orbit, than it is at the perihelion of Mercury’s orbit.

A quick and simple definition to the aphelion and perihelion, in case you’re unfamiliar with these astronomical terms.



“Aphelion (PSF)” by Pearson Scott Foresman – Archives of Pearson Scott Foresman, donated to the Wikimedia Foundation→This file has been extracted from another file: Aphelion (PSF).png.. Licensed under Public Domain via Commons –


The Aphelion: the point at which an object is farthest from the (star) object it is orbiting around. The Perihelion: the point at which an object is closest to the (star) object it is orbiting around.

Cool Facts About Mercury – Fact #7:

Mercury has the greatest amount of craters of any planet.

Because Mercury has been dormant for so long, it no longer possesses the natural geological functions needed to heal itself when its surface is hit by asteroids or comets. Much like our Moon, which also has a lot of craters and most of which are still predominantly observable given its inability to heal itself.



“PIA19420-Mercury-NorthHem-Topography-MLA-Messenger-20150416” by NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington – Licensed under Public Domain via Commons –


Most of the craters on Mercury are named after famous writers and artists.

If a crater is greater than 155 miles in diameter, it’s referred to as a basin.

Mercury’s craters and basins are also cool for another reason. Let’s check out the next cool fact about Mercury and see what it is.

Cool Facts About Mercury – Fact #8:

Mercury has water ice. Say what?

You’re probably thinking, how in the hell can Mercury have water ice on it, if it’s the closest planet to the Sun and the second hottest planet in our Solar System. Well it does, so believe it.

Here’s how. Mercury’s craters and basins are so deep, they actually shield the area inside of themselves from the heat of the Sun. So while surface temperatures facing the Sun can be extremely hot, the depths of the craters and basins near the planet’s poles keep the temperature low and the water frozen as ice.



“PIA19247-Mercury-NPolarRegion-Messenger20150316” by NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington – Licensed under Public Domain via Commons –


So where did this frozen water come from? Well, it’s not entirely known and currently under investigation by super smart scientists. However, the two leading theories are that either (1) the ice came about from what’s known as outgassing from the interior of the planet or (2) the water ice was brought there from any number of impacts from countless comets.

Cool Facts About Mercury – Fact #9:

We’ve only sent visitors to Mercury, twice.

First of all, by visitors I don’t mean astronauts, I mean any sort of spacecraft, satellites or any orbiters. Mercury isn’t’ that far away, you say, so why have we only sent two spacecrafts to visit Mercury?

Well, pretty simple. It’s tough to get to. Because Mercury is so close to the Sun, it makes sending objects to Mercury difficult and it makes keeping those objects in Mercury’s orbit from Mercury’s weak gravitational pull even more difficult.

Nonetheless, we humans are awesome and have achieved this difficult task… twice.



“PIA19419-Mercury-Messenger-MASCS-20150416” by NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington – Licensed under Public Domain via Commons –


The first spacecraft we sent to Mercury was the Mariner 10, which flew by Mercury 3 times in 1974 and 1975. Even though the Mariner 10 flew by Mercury 3 times, it was only able to map a little less than 50% of Mercury’s surface.



“Mariner10” by NASA / Jet Propulsion Laboratory – Licensed under Public Domain via Commons –


The second time we sent a spacecraft to Mercury was back in August of 2004 when the Messenger spacecraft was launched to Mercury. It arrived in April of 2011 and was the first craft to enter Mercury’s orbit.

The Messenger spacecraft took over 100,000 images and mapped 100% of Mercury’s surface. The Messenger spacecraft ran out of fuel and crashed into Mercury April 30, 2015 after a very successful mission.



“MESSENGER – spacecraft at mercury – atmercury lg” by NASA / JHU/APL – link. Licensed under Public Domain via Commons –


There are plans in the near future to visit Mercury again; BepiColombo. The European Space Agency and the Japan Aerospace eXploration Agency plan to launch two satellites to orbit around Mercury. The expected launch date is January 27, 2017 and will arrive at Mercury in 2020 and enter Mercury’s orbit in 2024.

Cool Facts About Mercury – Fact #10:

Mercury’s core is hella big! In relation to its total volume.

Ok, well Mercury is the smallest planet, so its core isn’t actually “big” by planetary measurements. However, relative to its total volume, it’s pretty big.

Mercury’s core is made of iron and is believed to be roughly 40% of the planet’s total volume. To put it into perspective, the Earth’s core is only about 17% of its volume.



“Internal Structure of Mercury” by Jcpag2012Mercury image: NASA-APL – Own worksource from Mercury Globe-MESSENGER mosaic centered at 0degN-0degE.jpg. Licensed under Public Domain via Commons –


As of 2007, Scientists believe that Mercury’s core is made of molten iron and has a radius of roughly 1,100 to 1,200 miles. This surrounds roughly a 310 to 435 miles thick radius of mantle made of mostly silicates. It’s believed that Mercury’s crust is 62 to 186 miles thick, which is pretty cool.

Other Random Cool Facts About Mercury:

  • Mercury orbits around the Sun at nearly 30 miles per second. That’d be the equivalent of traveling in your car at 108,000 miles per hour.
  • Mercury is named after the Roman messenger god, also known as Hermes in Greek mythology.
  • The closest Mercury comes to Earth is a measly 48 million miles away. Pretty far!
  • Astronomers didn’t realize Mercury was a planet until 1542 when Copernicus published his works proving the Sun was the center of the Solar System.
  • Mercury is made up of 70% metals and 30% silicates.
  • Diet tip: If you weigh 150 lbs on Earth, you’d only weigh 57 lbs on Mercury.
  • We can’t observe Mercury using the Hubble Telescope. Since Mercury is so close to the Sun, the brightness from the Sun would ruin the sensitive electrical components on the Hubble Telescope.
  • Astronomers once believed there was a planet which orbited the Sun between the Sun and Mercury, named Vulcan. However, such planet has never been found. Sorry Mr. Spock.
  • Mercury doesn’t experience any seasons. It’s just always hot as hell or cold as an Eskimo’s freezer.
  • Mercury rotates 1.5 times for each 1 orbit around the Sun. That’s because of the tight tidal lock the Sun has on Mercury due to its proximity to the Sun.
  • Mercury’s orbit was critical in helping scientists prove Albert Einstein’s theory of General Relativity.
  • Mercury has a very, very, very weak magnetic field. About 1% the strength of Earth’s magnetic field.



Featured image by “281521main flyby2 20081007 226” by NASA – NASA [1]. Licensed under Public Domain via Commons –

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