Planet Mercury interesting facts

What is planet Mercury? Is it something like your quiet neighbour, or is it something more than that. Today we will have a trip on Mercury, thus go through everything that can be called Fun facts Mercury.

Mercury is the first planet of the Solar System and also the smallest. The planet is named after Mercury, the messenger of the gods. Even though it is not known who discovered Mercury, the planet is mentioned for the first time in old Assyrian scripts that date back to the 14th century BC. For many years Mercury seemed to be “forgotten”, with the only mission visiting the planet being Mariner 10 in the 70s. But the recent MESSENGER probe has revealed many interesting facts about Mercury.   

Mercury planet profile – Interesting facts about Mercury

Mercury is located around 58 million km from the Sun. Initially, astronomers believed that Mercury due to its proximity to the Sun, is landlocked, just like the Moon. But, we know now that Mercury orbits around its axis and it takes 58.5 Earth days to complete an orbit with respect to the star, while one year is 88 days. But if you consider a Solar day (the amount of time that it needs for the Sun to appear at the same position in the sky), then one day in Mercury is 176 days.

At first glance, Mercury resembles the Moon. Note though that Mercury’s surface is much darker.

Just like Earth, Mercury is a terrestrial planet, made out of 70% metallic and 30% silicate material. Due to this Mercury is the second most dense planet in the Solar System at 5.427 g/cm3 (Earth  5.515 g/cm3). The radius of Mercury is 2440 km (40% of Earth’s radius), which means that Mercury is the smallest planet in the Solar System. The mass of Mercury is around 3.3×1023 kg (6% of Earth’s mass), while gravity is also around 38% of Earth (3.7 m/s2). Thus, Mercury is larger that our Moon, but is smaller than Jupiter’s satellite Ganymede. The surface of Mercury is highly bombarded by comets and asteroids  and at first glance you consider it looks like the Moon. Finally, Mercury has no natural satellites (just like Venus.)

Why Mercury is not the hottest planet?

Plenty of people may think that Mercury is the hottest planet in the Solar System, since it lies closest to the Sun. The truth though is different, since Venus is the hottest planet and there is a reason for this.

The surface temperature in Mercury varies between -180°C (-300°F) at night, to 430°C (800°F) during the day. The rotation axis of the planet is not tilted, thus the temperature in the polar regions is around −93 °C (−136 °F). Responsible for these temperature extremes is not only the slow rotation of the planet, but also the lack of an atmosphere (actually Mercury has a hint of atmosphere). Atmospheres can trap heat, something that we know from our Earth.Thus, the side of the planet that does not look at the Sun cools down rapidly.

To understand this better consider the following. You are sitting on a campfire wearing a coat. Here the fire is the Sun, while your coat is the atmosphere. If you sit close to the fire and remove your coat, the front part of your body still receives heat from the fire, but you feel that your back feels colder and colder. 

Does Mercury have ice?

If someone asks you to name a planet that you are really sure that does not have ice, for sure Mercury it will be a popular reply.

But what if you are told that water in the form of ice exists on Mercury? It sounds indeed unlikely, but observations from MESSENGER have confirmed this. The water on Mercury most likely came from comets, or even asteroids. The ice has been found in the polar caps of the planet, inside the craters, which are regions that Sunlight cannot reach.

Observations with MESSENGER have reveal the presence of ice on Mercury. These deposits are within the craters on the North and South poles of the planet, thus sunlight cannot reach there.

On Earth we can also have similar effects. Imagine that you are in a place that during winter snows a lot. During the summer most likely due to heat the snow melts, but if you check an Earth fissure, most likely you will come across ice deposits.

What is the structure of Mercury?

Observations on the interior of Mercury have revealed interesting things about the history of the planet. The composition of Mercury’s core is not similar to that of the Earth, but this is nothing compared to the planet’s history. The core of Mercury is overwhelmingly large with respect to the planet and there is practically no mantle like Earth.

Interior structure comparison between Mercury and Earth. Note the size of Mercury’s core and the fact that the planet has almost no mantle.

So, it is believed that the planet was much larger in the early Solar System. During that period loads of large bodies were floating around the Sun colliding with each other. So somehow, Mercury lost a significant amount of its mass.

The first model suggests that Mercury collided head-on with a planet the size of the Moon. But once again the MESSENGER probe had a different opinion. A head-on collision will practically set the whole planet on fire. The surface of Mercury is rich in chemical elements like potassium. A head-on collision will practically set the whole planet on fire. Thus, like potassium will evaporate, which is not the case in Mercury.

This led to an even more interesting scenario. A planet the size of the Earth (it could be Earth actually), had an overlap collision with Mercury, from which the planet lost a significant amount of mass, but was able to retain elements like potassium. So, you may actually walk on Mercurian soil.

Why is Mercury shrinking? – The smallest planet is getting smaller.

It may sound strange, but Mercury is shrinking. Until 2004, the only probe that has given detailed observations of Mercury was Mariner 10. Surface photos have revealed the presence of fault scarps, which can extend up to 1000 km in length and around 3 km in terms of height. Similar faults are present on Earth and their formation is due to tectonic plates activity. Mercury’s crust does not have tectonic plates, thus these faults are due to the shrinkage of the planet.

New small scale scarps on the surface of Mercury. These structures suggests that the planet is still shrinking.

This happens due to the cooling of the  planet’s core and from basic physics we know that when metals cool down they shrink. To understand this better just imagine the following. You have a balloon, which you cover with mud. Once the mud dries, you let air out of the balloon. The balloon will shrink, but the mud (Mercury’s crust here) cannot shrink since it is solid, thus as the balloon shrinks fault scarps will be formed. But these large-scale faults are old, since they show evidence of comet bombardment.

In 2012 observations with MESSENGER revealed the presence of new small fault scarps (around 100 meters in length), providing evidence that the planet is still shrinking. The fact that they are indeed young, comes from the fact that they are not bombarded by comets. This makes Mercury, the only planet in the Solar system apart from Earth, that shows geologic activity. The current estimate is that since its formation, Mercury has shrunk around 10-15 km. So it seems that the smallest planet in our Solar system is getting smaller.

Future missions to Mercury

Mercury is a planet that has an interesting story to tell. The planet most likely has been reformed by a spectacular collision, and it seems that it is still shrinking. Finally, prior to MESSENGER’S discovery no one would have thought that there is ice, on the closest planet to the Sun. At the moment, BepiColombo, a joint mission of the European Space Agency and the Japan Aerospace Exploration Agency, is on its way to Mercury. The probe will conduct further studies on the surface and structure of the planet. So it is a matter of time to see whether, or not, Mercury has any further surprises.


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16 thoughts on “Planet Mercury interesting facts”

  1. Hi Anestis,

    Great post. Thank you for the fun adventure I had while reading. I always feel so small when reading about these topics. I am looking forward to what you are posting next.

    • Hi Dwayne,

      I would like to thank you for visiting my webpage and your positive comments. In a way it is true, if you try picture our location in our galaxy and consider only this, you get to see that we are not even a dot there. The Universe is huge and we cover no special area, but according to the strong anthropic principle of cosmology according to Barrow and Tipler: “The Universe must have those properties which allow life to develop within it at some stage in its history.” So perhaps, there is a reason, why we exist.



  2. Thanks for this article. Mercury is not one of the most talked about planets in our solar system, so few people know much about it. I learned stuff about Mercury here that I did not know before, and I enjoyed reading it.

    More articles like this and I’m sure to come back.

    Any idea how much longer before the BepiColombo mission reaches Mercury?

    • Hi Frank,

      Thank you for your positive comments and for visiting my webpage. It is true that Mercury was forgotten for many years and it was good that NASA sent MESSENGER there. BepiColombo will arrive on Mercury around 2025. I wonder if this mission will reveal any new interested things about Mercury.



  3. I really like the format and the content on your website. From reading only one blog post I can tell that you are passionate and educated in your chosen niche. You have done a great job loading your website up with tons of content (blog posts) that consumers can read. I really liked how you put captions on your pictures. This is a little detail that makes blog posts more professional and helps bring clarity to your posts. All the pictures you chose to present were relevant.

    Keep on rockin

    • Dear Jacobus,

      I would like to thank you for your time and visiting my page. My plan is to continue with such posts. I hope that with time my knowledge on webpage hosting will also improve, thus I can make my page look better.



  4. Hey Anestis, some very interesting facts here about Mercury. Anything to do with our solar system interests me and whether life existed or maybe still does?

    If there were life on any of the planets, we would be the last to know with so much secrecy that goes on in Governments and Government agencies.

    Although when you look on a map the distance to the sun seems very close but it really isn’t.

    I wonder with the size of the planet and distance from the sun that it would get pulled in?

    Thank you for sharing


    • Dear Mick,

      Once again thank you for visiting my webpage. In terms of life existence in other planets in our Solar system, we are only certain that there is no life in Mercury, Venus, and Mars. What plenty of Solar system scientists would like to do, is to check if there is life in Europa (satellite of Jupiter) and Titan (satellite of Saturn). Even we find life in the form of bacteria will be something more than incredible.

      If a probe visits Europa, or Titan for checking if there is life and finds something, it will be impossible for this to be hidden. There are a lot of people involved into a probe-mission, thus someone, if not all of them together, will come out and announce it.



  5. Hi Anestis,

    I must admit that I’m pretty confused about the positioning of the planets. What’s really surprising in your article is that Mercury isn’t the hottest, despite being closest to the sun.

    Seems to defy the law of nature but I guess that’s what makes the universe mysterious and wonderful. Thanks for the lovely read.

    • Dear Kenny,

      First of all I would like to thank you for visiting my page and your comments. Regarding now the hottest planet of the Solar System, it is simple why Venus is the one and not Mercury. Venus has a very thick atmosphere. Venus’ atmospheric pressure is 92 times higher than Earth’s. Thus, the atmosphere of Venus will trap much more heat than Mercury (Mercury has just a hint of an atmosphere). Also Venus’ atmosphere is composed mostly from carbon dioxide that enhances the greenhouse effect. Finally, if the Earth didn’t have an atmosphere, the mean temperature would be -15C, or around 5F.

      Thus, it is not only the distance from the host star that will provide evidence from the surface temperature of a planet, but also the atmosphere of the planet, together with its composition (rocky or gaseous).

      Regards, Anestis

  6. Wow very interesting, before reading this post I only knew Mercury as a planet, after reading your post I have come to realize some cool facts about Mercury. The examples of Campfire and Balloon were apt…I would love to hear from such cool facts on other planets. This was truly informative for me.

    • Dear Satz

      Thank you for visiting my page. I believe that sometimes you have to bring the simplest possible example in order to explain something. My plan at the moment is to make a series for the whole Solar system. I hope that you find it useful.

  7. Hi Anestis,
    Really informative article.

    I am fascinated by the fact that mercury is shrinking and learning that since its formation it has shrunk between 10 and 15 km. This is huge! I am curious to know if it continues shrinking, if it were to be hit by a comet, could it totally disintegrate at some point in time?

    By the way, I love your images of Mercury.

    • Hi Ceci,

      I would like to thank you for visiting my webpage and for your comments. Mercury will continue shrinking as long as the core continues to cool down. Comets are small, thus they can cause only small scales damages*. But if an asteroid (their size can be up to a couple of hundreds of km) hits Mercury, then the damage will be more devastating. But none of these can destroy the planet.

      The small scale has to do only with the planet. If a comet with radius around 10 km hits the Earth, I don’t think we will have many witnesses!



  8. This is an amazing and extremely interesting article on Mercury, and I was one of those who thought Mercury was the hottest planet being the closes to the sun. I really found your website unique and interesting, so you can be sure I will be returning frequently


    • Dear Jeff,

      I would like to thank you for visiting my webpage and for your review. Indeed Mercury seems to confuse a lot of people, scientists included. I wonder if BebiColombo, will reveal any new interesting facts about Mercury, in 2025. Only time will show.




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