As the smallest planet in the Solar System, and the closest planet to the sun, Mercury is just a little bigger than the moon that we see every day. Though it is the closest planet to the sun, it is not the hottest, which will be explored later. Along with Mars, Venus, and our own Earth, Mercury is a planet that is made out of the rock. The surface of Mercury is solid, and it is covered throughout with craters. The atmosphere is very thin, and Mercury does not have any moons to speak of.
Another interesting fact about Mercury is how slow it spins when compared to the spin of the Earth. Our planet makes a full rotation every 24 hours, but on Mercury, things are very different. It moves very slowly, so it actually takes 59 days to rotate fully! On the flip side, a year on Mercury goes by very quickly as it has a much shorter distance to travel when compared to Earth. It only takes 88 days for Mercury to travel around the Sun. Thanks to the slow rotation speed and the speed in which a year passes, it takes a really long time for the sun to rise and set on Mercury. So, oddly enough, there is only one sunrise every 180 days!
There are only a few of the amazing facts that we can tell you about Mercury, so you have to keep reading to find out more and to learn the top 10 facts about Mercury:
10Mercury Has Been Known of Since Ancient Times
Unlike most of the other planets in the Solar System, Mercury has been known of since ancient times. We don’t know who, if anyone, ever discovered Mercury, but we do know that it has been known of for at least 5,000 years, as the first records of the planet come from the Sumerians. The Babylonians also recorded their knowledge of Mercury in records that date back to around 1,000 BC. They called Mercury, Nabu, which was the name of their mythological messenger to their gods.
We also know that both the Greeks and Romans knew about Mercury, and in fact, we still use the Roman name for the planet, today. They must have known about the Babylonian name for Mercury, too, because Mercury was their own messenger to the gods.
“The Hour Star” was what the ancient Chinese called Mercury, and they associated it with the north. Additionally, we know that the ancient Koreans, Vietnamese, Japanese, Hindus, Mayans, and the Germanic people all knew that Mercury existed thanks to records. Many of these cultures associated Mercury with their mythology. However, and this is very interesting, the Mayan’s used an owl to represent Mercury, and this, too, was symbolic of a messenger, though in this case, it was a messenger to the underworld.
We can understand why the ancient Romans and Sumerians might have had the same meaning behind their version of Mercury. We know, thanks to records, that the Sumerians had a big influence on the Romans. However, it’s a mystery as to how the Mayans would have the same knowledge.
9Mercury is Not the Hottest Planet
Thanks to its close proximity to the Sun, most people believe that Mercury is the hottest planet…but it’s not! That actually goes to Venus, which is a full 31,248,757 miles away from Mercury! How can this be? Let’s take a look. First, let’s look at the average temperature on both planets. The average temperature on Mercury is a steamy 332 degrees F, but it can get up to 800 degrees when the surface is facing the Sun. Venus has an average temperature of 864 degrees F, day or night. But why?
It has to do with the atmosphere of Venus. We already mentioned that Mercury has a thin atmosphere, but the atmosphere of Venus is much thicker. Basically, it is like Venus has a blanket on, which keeps the heat in, and Mercury doesn’t. Both of these planets get a lot of heat from the sun, but since Mercury doesn’t have a “blanket,” in the form of a thick atmosphere, the heat escapes. Venus, however, keeps heat inside thanks to the thick atmosphere, thus, it is hotter.
This is similar to how a greenhouse works on Earth. The light and heat from the sun come into the greenhouse, but it can’t get out thanks to the windows, which make up the entire structure. So, we can say that Venus is like the greenhouse of the Solar System.
8Mercury is the Smallest Planet in the Solar System
When we look at our Solar System, there are planets of all sizes, and there are all types of possibilities in regard to how the planets form. We already noted that there are four planets made of rock, including Mercury. These are known as the Terrestrial Planets. The rest of the planets are made of gas and known as the “gas giants.” So, as you can imagine, the terrestrial planets are smaller than the rest.
You might think that it would be easy to say that Mercury is the smallest planet, but there is a bit of controversy around this. Until 2006, Mercury was not the smallest planet, it was the second smallest planet…so what happened? Up until then, Pluto was the smallest planet, but thanks to an IAU Resolution, which changed the definition of a planet, Pluto was no longer considered to be one. So, this meant that Mercury was now the smallest planet, not the second smallest, in the Solar System.
Mercury only has a radius of 1,516 miles and is only about 0.38 the size of Earth. When you consider that the distance from New York City to Denver, Colorado is about 1,700 miles, you can really get a picture of how small Mercury actually is. In fact, Mercury is smaller than some of the moons in our Solar System including Titan, a moon of Saturn, and Ganymede, a moon of Jupiter. Thanks to the fact that Mercury is almost a perfect sphere, we can get great measurements of this planet, as it is almost the same no matter where you measure.
7Mercury Has Only Been Visited by Us, Twice
You might be surprised to learn that there have only been two missions to Mercury, and there is a good reason for that. First, for some reason, we haven’t been very interested in the planet. There is nothing really special about it, like the Big Eye of Jupiter or the red surface of Mars, so we haven’t had a lot of reason to go. Second, it is so close to the Sun that it’s difficult to get something like a satellite into orbit, as the Sun would suck it right in. There have, however, been two missions, and one, which was launched in 2018, which is on the way.
The first mission, Mariner 10, was launched in 1973 and the focus of the mission was to take photos of Venus and Mercury. The data from this probe showed that there was a magnetic field around the planet and that approximately 80 percent of the mass of Mercury is made of a metal core.
The second mission, MESSENGER, was sent towards Mercury in 2004, and it finally entered the orbit of the planet in 2011. This mission was able to get images of the entire surface and was further able to get information on the core and atmosphere. The newest mission, BepiColombo, is scheduled to get to Mercury in 2024 and is a mission sent by the Japan Aerospace Exploration Agency and the European Space Agency.
6Mercury Has Almost No Atmosphere
We have already mentioned that Mercury doesn’t have a very thick atmosphere, which is why it is cooler than Venus. But the actual atmosphere is so thin that it almost doesn’t even exist! Because of this, it is 10,000,000,000,000,000 times less dense than the atmosphere on Earth, and it is almost a true vacuum. There is, however, an explanation…
The main reason for the lack of an atmosphere has to do with both gravity and the close proximity to the Sun. The gravity on Mercury is only about 38 percent of the gravity that we are used to. So, on Mercury, a 200-pound person would only weigh 76 pounds. Because of this lack of gravity, however, the planet is just unable to keep an atmosphere in the place. The other reason, the close proximity to the Sun, makes it difficult for Mercury to even accumulate an atmosphere because the planet is almost always being hit by the solar winds of the sun, which removes almost all of the atmosphere that it is able to gather.
Even though the atmosphere is a bit on the thin side, the planet does, indeed, have one. It is mostly made of oxygen, which makes up 42 percent of it. Other chemicals found in the Mercurian atmosphere include sodium, hydrogen, helium, potassium, and trace chemicals. It is the hope that the upcoming BepiColombo mission can learn more about the atmosphere of Mercury.
5Mercury Has More Craters Than Any Other Planet
If you look at pictures of Mercury, you will definitely notice all of the craters on its surface. In fact, many people say that it looks very similar to the surface of our moon. So, why are there so many craters on Mercury but not as many on the other planets? It all goes back to that Mercurian atmosphere.
The first thing that you have to know about this is that the gas giants, Saturn, Jupiter, Uranus, and Neptune, are made of gas, so they do not have any craters because there is no surface. The other planets, Venus, Earth, and Mars, do have craters and have in the past, but very few when compared to the craters on Mercury and the Moon. Why is this the case? Well, it’s because Venus, Earth, and Mars all have atmospheres, and within those atmospheres, there is the weather. If you think about what you know about the Earth’s atmosphere, it snows, rains, gets windy, etc, and all of that, over time, changes the surface. So, when a crater appeared, the Earth’s weather took care of it. It is the same with Mars and Venus.
Mercury and the Moon do not have weather. So, there is nothing to “erase” the craters that have formed. It is believed that there are thousands of craters on Mercury, and they are still in the process of being categorized…and here’s another bonus fact…many of the craters that have been categorized are named after famous composers from Earth.
4The Core of Mercury is Absolutely Huge!
If you know anything about the Earth, you might know that it has a core or a center. It is a little over 1,800 miles below the surface, and it is extremely hot, reaching temperatures of more than 10,000 degrees F. However, it makes up only about 17 percent of the total volume of the plant. Mercury is very different.
For many years, scientists believed that the core of Mercury was made of solid iron. But, thanks to research, they now believe that it’s possible that the core could be molten, just like the core of the Earth. Generally, the core of a small planet cools quickly, but now, after a lot of research into it, scientists do not believe that the core is as cold as they first thought. Today, the researchers believe that the core is not made of iron, at all. Instead, it is probably an element that is lighter, like sulfur. This would mean the melting temperature is lower, thus a molten core.
Now, for the most interesting fact of all. It is believed that the core of Mercury makes up over 40 percent of its volume! That’s a huge amount, and it tells us that Mercury could be made up of half a molten mess that is found right below the surface.
3Mercury is a Survivor
We have already talked about all of the craters on Mercury. These are caused by asteroids and meteorites. So, you can tell how large the asteroid or meteorite that hit the planet was based on the size of the crater. Now, consider this…one of the craters on Mercury is absolutely huge. It is approximately 960 miles across, in fact. How big is that? If you took the state of Texas, it would fit right inside that crater. This means that the asteroid that hit Mercury had to be a least 60 miles wide. Since Mercury is such a small planet, an impact like this could have been devastating.
The crater that was created by this huge impact is known as the Caloris Basin. It is believed that lava flows through the basin and that it is between 3.8 and 3.9 billion years old. Researchers also believe that when the impact happened, one of two things could have happened:
First, it could have caused seismic waves, which were so powerful that it created hills and groves on the opposite side of Mercury. The second thing that could have happened is that the impact could have been the cause of volcanic activity, which created the plains around the crater. We may not ever figure it out, but again, one of the objectives of the BepiColombo mission is to examine these craters, including this one, so hopefully, we will get more information on it in the future.
2Mercury Might Have Water
According to NASA, Mercury has the most extreme temperature fluctuations in the entire solar system. The side of Mercury that is facing the sun, can get up to 800 degrees F. However, on the other side of the planet, it’s a very different story. This is pretty shocking, but on the side of Mercury that does not face the sun, it can get very, very cold. In fact, it can get as cold as – 290 F, and these variations can last a long time. Why is this the case, though?
Here on Earth, we have seasonal temperature shifts, which are caused by the tilt of the Earth’s axis. When the Southern Hemisphere is closer to the Sun than the Normal Hemisphere, for instance, it is spring and summer. At the same time, up north, it is fall and winter. Mercury does not have a tilt, though. So, there is no difference in one hemisphere to another, which means there is no difference in temperature in the north and south.
Because of this, Mercury might have ice on the surface around the north and south poles of the planet. This is because the poles never face the sun since there is no tilt. We know, thanks to telescopic observations, that there are also bright patches inside of the craters, which were mapped in the 70s by Mariner 10. When MESSENGER studied the surface of Mercury, again, we could see the bright spots, which looked very similar to the spots at the poles. In 2012, there was further research, and MESSENGER used neutron spectroscopy to find out that there were concentrations of hydrogen in these bright areas, which makes the case for water even more plausible.
1Mercury Isn’t Easy to See from Earth, but It’s Possible
Many people believe that Mercury shouldn’t be too difficult to see with the naked eye. After all, if we can easily see planets like Jupiter without a telescope, which is 365 million miles from Earth at its closest, we should easily see Mercury, which is only 48 million miles from Earth. This, however, isn’t true. In fact, Mercury is the most difficult planet to see, but there is a good reason for this.
Unlike the other planets, Mercury doesn’t ever appear too far from the horizon. This is because of its close proximity to the Sun. In general, this isn’t a huge deal, but you have to think of how far out we are when compared to Mercury. When you calculate everything, Mercury is just 28 degrees from the Sun as we can see it from Earth. Since Mercury is so close to the Sun, and at this weird angle, it makes it almost impossible to see it from Earth…but there is a chance if you do it the right way.
Basically, you have to watch the movements of the planets, and you have to be outside and looking up at the exact right time. You can usually only see it as the sun is setting or rising, and you have to look just below the horizon. Mercury usually looks a little pink or rosy in color, but it is bright. These windows don’t happen very often, so if you have the chance to see it, take advantage of it.
Mercury is the smallest planet in the Solar System, and it is the closest planet to the Sun. It is also one of the most mysterious planets, which makes it so fascinating. Though we don’t know much about the planet right now, we are hoping for more information on Mercury in the next few decades thanks to new exploration opportunities.
One of the things that could be really significant about Mercury is the possibility of water on the planet. Though human life couldn’t exist on Mercury due to the temperature and atmosphere, it’s possible that other forms of like could have evolved. There are actually living things here on Earth that can live in high heat, such are microbes, so it isn’t out of the question that there could be, or could have been, life on Mercury.
With BepiColumbo on its way to Mercury, and scheduled to arrive in 2025, we are only a few years from getting more information on what is really happening there. In the meantime, we can continue to rely on research we can do from Earth, including using things like high-powered telescopes and satellite images in addition to data from previous missions.