As a child, I loved astronomy. It fascinated me that I could look up at the night sky and see Venus, Mars, Jupiter and Saturn moving across the heavens. I was always frustrated that I could never see Mercury, though.
For some reason, I believed that it was as remote as Pluto. It must be, I thought, equally unknowable without a telescope.
As an adult, I learned that this isn’t the case at all. The closest planet to our sun – the star we call Sol – is actually visible on many clear nights. Glowing like a blazing red star, it is often mistaken for Mars. (At least, it was by this amateur astronomer!)
A bit of chatroom surfing makes clear that many people feel the same. Mercury is nearly twice as close to us as Mars, but you’d never know it. Perhaps its barren nature makes it seem so alien. Or perhaps it just hasn’t gotten enough love.
Well, let’s change that. Read on for 15 fascinating Mercury facts that everyone should know!
1. The Romans Named Mercury After a God
Okay, this fact is true of all the planets. The word “planet” comes from the Ancient Greek planētēs, meaning “wanderer.” The ancients noticed that the planets moved strangely across the background of the stars. Hence, they earned the name.
This became the Latin word planeta. The Romans then named them after their gods. In addition to deities of war, love, time and so forth, Mercury was the winged messenger of the heavens.
2. It Orbits Faster Than Any Other Planet
Its name doesn’t come out of nowhere. Mercury moves very fleetly through the heavens, circling the sun faster than any other planet. According to NASA, it only takes 88 days to make a full rotation.
Additionally, it travels through space at 29 miles or 47 kilometers per second. That’s faster than any other planet. For reference, compare that to Earth. It moves at a relatively stately 18.5 miles or 28 kilometers per second.
3. Mercury Is the Smallest Planet
Mercury used to carry the title of second-smallest planet. However, the International Astronomical Union downgraded Pluto from planet to dwarf planet in 2006. (Fun fact: renowned astrophysicist Neil deGrasse Tyson gets hate mail from third-graders about his role in Pluto’s fall from grace.)
There’s one dubious winner of this development, though. It’s Mercury. Now the littlest planet in our solar system, it is still large compared to Pluto.
4. … But It’s Not as Small as You Think
Despite its relative tininess, Mercury isn’t as small as most people think. If you compare it to a nickel representing the Earth, it is blueberry-sized.
That’s pretty chonky for the smallest planet. It helps partially explain that it is indeed visible against the night sky. (One wonders how certain amateur astronomers could ever have missed it.) That, and the fact that it’s not that far from Earth.
5. It’s Not That Far From Earth
Oh, um, did we mention it’s not that far from Earth? Most of us are used to hearing about Mars, probably because it is the most colonizable planet. Because of its geologic composition and distance from the sun, Mars is ripe for terraforming.
This sometimes leads people to wrongly associate Mars with proximity. However, the Red Planet is an average of 140 million miles from Earth. This translates to roughly 225 million kilometers. On the other hand, Mercury’s average distance is only 48 million miles or 77 million kilometers.
Sure, we’re not going to colonize it any time soon. It’s a total hellhole, after all (more on that below). But that still makes it a pretty close neighbor!
Related: Earth vs Mercury (similarities and differences)
5. Mercury Has an Egg-Shaped Orbit
We think of planetary orbits as circular. However, most take the form of an ellipse. This is an elongated circle. Some are more elongated than others. In Mercury’s case, its orbit is so squished that it is egg-shaped. Plus, one side of its orbit is closer to the sun than the other.
This has to do with the sun’s closeness and the effect of its magnetic fields. The result is that it is sometimes much farther away from the sun than other times. It comes as close as 29 million miles (47 million kilometers) and gets as far as 43 million miles (69 million kilometers).
6. It’s One Hot Tamale
Mercury has no almost atmosphere. That means it is incapable of keeping in warmth or keeping out heat. This makes it a planet of extremes.
According to the National Weather Service (NWS), Mercury gets up to 800 degrees Fahrenheit on its day side. That’s 426 degrees Celsius, meaning that during daylight, Mercury is more than twice as hot as needed to cook a chicken.
The nighttime side is different. It’s colder than any desert on Earth by far. Due to the lack of atmosphere, it plummets to -330 Fahrenheit or -200 Celsius. That’s nearly as cold as the densest gas clouds that inhabit the space between stars. Visitors, bring your parkas!
7. … But It’s Not the Hottest Planet
You’d think, given its nearness to the sun, that Mercury would be the hottest planet. Yet that honor goes to Venus. The surface ranges from 820 to 900 degrees Fahrenheit, says the NWS. The average temp is 847 Fahrenheit, or around 453 Celsius. That’s hot enough to turn lead into a liquid.
This is a powerful demonstration of the difference between having an atmosphere and not. Because Mercury lacks one, it has almost no surface pressure. Lower pressure = lower temperature. Plus, it can’t trap heat.
Because Venus’s atmosphere is so thick, however, its surface pressure is extreme. It also traps tons of heat. That leads to much higher temperatures.
8. The Daytime Sky From Mercury Is Awesome
We think of “daytime” and “blue sky” as synonymous. But that’s only because the molecules in Earth’s atmosphere affect sunlight in a specific way. This creates the blue color. Additionally, the thickness of our atmosphere means we cannot see space beyond, like we can at night.
On Mercury, that’s not the case. You can see all the stars glimmering in the daytime sky, just as at night. However, you would also see the sun. And on Mercury, it appears more than three times as large and seven times brighter. Bring your shades too!
9. Mercury Isn’t Impossible to Terraform
Arthur C. Clarke, the famous science fiction writer, once remarked that “Any sufficiently advanced technology is indistinguishable from magic.” In other words, until a technology is real, it seems impossible. Just take a look at the history of the airplane.
Today, it’s hard to envision living on Mercury. How could we make it habitable? How could even the most cutting-edge science deal with temperature and radiation problems? Is terraforming even possible? Surprisingly, the answer is yes.
The answer is, scientists and colonists would face extreme challenges. However, Mercury is rich in minerals. It has a thin crust, so those minerals are relatively easy-access for people on the surface.
It also has hollows, which may indicate lava tubes that could shield people from radiation and heat. It may even have ice at its relatively cool poles.
Could we one day move to Mercury? Maybe so.
10. People on Mercury Would Be Known as “Hermians”
Earthlings who move to a terraformed Mercury are still human, but they’re no longer Earthlings. Instead, we’d become “Hermians.”
If you know your Greek mythology, chances are you already know why. The Roman god Mercury is actually an adaptation of an older god, Hermes. He too had winged sandals on his feet and was the fastest of all the gods in the Greek pantheon. (A pantheon is a collection of the gods of a specific culture.)
Thus, people living on The Swift Planet would bear the hallmark of their home world in their names.
11. You Can See Mercury Against the Sun
A transit is when a planet moves across the surface of the sun from the viewpoint of another planet. From Earth’s vantage point, Mercury crosses the sun 13 times per century.
When it does, it appears as a small black dot moving across the surface of the massive sun. A transit takes several hours and is a pretty neat experience.
The most recent Mercury transits took place in 2003, 2006, 2016 and 2019. Because they are unpredictable, you have to know when to expect them. The next won’t happen until November 13, 2032. Looks like you have plenty of time to prepare!
12. We’ve Known About Mercury for a While
Despite its small size, Mercury made itself known early in the pioneering days of telescope invention and observation, first coming to the attention of famed astronomer Galileo Galilei. (Incidentally, he also invented the telescope, so he had a front-row seat if anyone did.)
Thomas Harriot observed it at the same time in 1631.
For centuries after that, scientists believed that Mercury was tidally locked, which is when an orbiting body always faced the same side of its parent body. This occurs when its rotations are synced up with the parent body’s revolutions. Think of the moon, which only ever shows us one side.
However, we now know that Mercury is not tidally locked. It actually rotates three times for every two revolutions of the sun.
13. Mercury Is a Sci-Fi Setting
Despite its general hellishness of today, Mercury isn’t unknown to sci-fi buffs.
As early as 1905, William Wallace Cook’ wrote Adrift in the Unknown, or Adventures in a Queer Realm, a novel that takes place on Mercury. The short story “The Lord of Death” by Homer Eon Flint imagines what it would be like if an advanced civilization, now extinct, were to have lived there.
Other potential readings for the lover of vintage sci-fi include:
- The Immortals of Mercury by Clark Ashton Smith
- Runaround by Isaac Asimov
- Tama of the Light Country by Ray Cummings
14. Learn to View Mercury
Mercury is visible to the naked eye at dawn and dusk. The best time to look for it is just before sunrise in the morning, or you can also search for it about an hour after the sun sets. Here’s a quick guide to finding planets in the sky, including The Swift Planet.
A good trick for telling the difference between a planet and a star is whether it twinkles. While stars seem to glimmer and blink, planets do not. This has to do with their distance from Earth: starlight is so far away that the beam of light is much smaller. This allows the atmosphere to bend it.
However, a planet’s light beam is comparatively huge. That allows it to maintain its shape as the light moves through the atmosphere. Mercury will look like a bright yellow or ochre star, minus the twinkle.
If you’ve made it to the bottom of the page, kudos! Hopefully, you feel a little closer to Mercury now. So next time you look up at the night sky, see if you can spot our winged friend.