Mercury — the Smallest Planet in the Solar System

So, let’s start our journey through the Solar System with Mercury — the closest planet to the Sun. It’s also the smallest planet in the Solar System, but it isn’t the tiniest in the Universe. What are Mercury’s features? Let’s find out!

The Basic Features

Let’s quickly discuss its fundamental specialties first. We already know something from the introduction, but how close is it to the Sun? How big is it?

In reality, Mercury is about 60 million kilometers from the Sun, meaning it’s 0.4 astronomical units from our star. It’s also insanely small compared to the exoplanets we’ve discovered because its diameter is 4,880 kilometers.

Moreover, it’s orbital period is 88 days, and its velocity is about 47 km/s. Meanwhile, it rotates once every 59 days, producing a 2:3 ratio between its day and year. Therefore, Mercury experiences a sunrise-sunset cycle only once every 176 Earth days, approximately 2 years on that planet.

Additionally, the planet has no seasons because its rotational axis is about 2 degrees.

Mercury’s Surface and Atmosphere

The planet has a weird structure and surface that no one who isn’t familiar with astronomy will expect.

Firstly, it has a very rough surface with many craters since it has no atmosphere. The planet contains an exosphere (a molecular cloud surrounding an object due to gravity). It’s made of hydrogen, helium, sodium, oxygen, and potassium. Because of the lack of air, temperatures on Mercury vary greatly. It can be as hot as 430 Celsius in the daytime, while it’s -180ºC at night.

Note: Mercury is NOT the hottest planet in the Solar System. Venus is hotter than that, clocking at around 471ºC. (NASA Solar System Exploration, 2019).

Amazingly, Mercury is still shrinking although all other planets is in an almost fixed size. The MESSENGER spacecraft detected scarps on Mercury’s surface, which are some “cliff-like landforms” (Bill Keeter, 2016). The features of these landscapes make scientists believe that the planet is still getting smaller. In short, Mercury is tectonically active like Earth.

Mercury’s Composition and Structure

According to National Geographic, the planet has a strangely colossal core: It accounts for 85% of its radius. This exceptionally large core may cause the planet to contract. (National Geographic, 2018). As a result, the planet may even be a piece of wreckage of a broken planet in a planetary collision.

As mentioned, the planet’s atmosphere is made of common gases and unusual alkali metals. But, how about its enormous core?

The planet has an iron core that generates its magnetic field that is only 1% as powerful as Earth’s. Like Uranus’s and Neptune’s, Mercury’s magnetic field is also off course, misaligning with the equator.

Mystery: Ice Inside Mercury?

There is some water ice on this extreme world. One of the sources is in the poles, where sunlight cannot shine on these locations well. Pretty simple, right?

However, there is a more complicated algorithm, and they involve some mysterious chemistry. First of all, the solar wind is too strong for Mercury to withstand, so they absorb some protons, which are positively charged particles.

After that, the hydrogen ions (protons) collide with the hydroxyl groups, which are ions with one oxygen atom and one hydrogen atom. Voila! Water particles (H2O) are formed. Some water molecules land on the dark places mentioned before and can neither melt nor decompose.

Mercury’s Explorations

Finally, we head to the exploration of the smallest planet in the Solar System. It’s burdensome for any space probes to arrive in that scorching spot. So far, only two spacecraft have visited Mercury. They are Mariner 10 and MESSENGER, respectively.

What’s more, Mariner 10 is a flyby mission. Therefore, it was not staying around the planet for long. However, both probes returned valuable information about Mercury.

Moreover, the closest planet to the Sun is tough to observe from Earth. Thus, our knowledge of that planet isn’t rich relative to other planets in the Solar System.

Conclusion

So, here’s a brief introduction to Mercury — the smallest planet in the Solar System. We hope you’re also interested and want to learn more from the references.

References and Credits

1. (2020, January 21). In Depth | Mercury – NASA Solar System Exploration. Retrieved December 25, 2020, from https://solarsystem.nasa.gov/planets/mercury/in-depth/
2. National Geographic. (2018, September 7). Mercury 101 | National Geographic – YouTube. Retrieved December 25, 2020, from https://www.youtube.com/watch?v=0KBjnNuhRHs
3. Bill Keeter. (2016, September 26). The Incredible Shrinking Mercury is Active After All | NASA. Retrieved December 25, 2020, from https://www.nasa.gov/feature/the-incredible-shrinking-mercury-is-active-after-all
4. Nola Taylor Redd. (2016, October 14). What is Mercury Made Of? | Space. Retrieved December 25, 2020, from https://www.space.com/18643-mercury-composition.html
5. (2019, December 19). In Depth | Venus – NASA Solar System Exploration. Retrieved December 25, 2020, from https://solarsystem.nasa.gov/planets/venus/in-depth/

Image Credits: NASA’s Eyes, Canva