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 fun facts proving that Mercury is a trickster indeed.
Mercury in number
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.
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 is Mercury 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 you will see why.
The 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 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.
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.
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?
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.
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.
Future of 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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