Mystery of the smallest planet in the Solar System

Mercury is the smallest planet in the Solar System family - Photo: Theosophy online

The planet with the most iron in the Solar System

Mercury is one of the four rocky planets like Earth, and is also the smallest planet with a diameter of only about 4,879.4 km.

This is 0.383 times the diameter of Earth and is even smaller than Jupiter's moon Ganymede and Saturn's moon Titan.

Iron makes up a large portion of Mercury's composition. It is also the most iron-rich planet in the Solar System.

Along with Venus, Mercury has no natural satellites, while the other planets all have satellites orbiting them.

Day and night temperature range is about 600 degrees Celsius

Mercury's atmosphere is extremely thin - Photo: NASA

Mercury is also the closest planet to the sun of the eight planets, at a distance of about 57.91 million km. This, along with its small mass, makes its atmosphere very thin, unable to retain heat.

Therefore, the temperature range between day and night on Mercury is the largest in the Solar System. At night it can drop to -173 degrees Celsius but during the day it can reach 427 degrees Celsius. The temperature range between day and night is up to 600 degrees Celsius.

Also because of the very thin atmosphere, Mercury does not have seasons like the four seasons on Earth.

Mercury's orbit is an extremely narrow ellipse with a major axis radius of 70 million km and a minor axis radius of only 46 million km. This is also a cause of the large temperature difference for Mercury.

A day is 2/3 of a year long.

A year on Mercury is only 88 days on Earth - Photo: NASA

Mercury orbits the sun very quickly, about 88 Earth days. Meanwhile, Mercury needs about 58 Earth days to rotate on its axis.

So, a year on Mercury is too fast, only 88 days compared to 365 days on our planet, and a day is incredibly long, equal to about 2 Earth months.

In other words, a Mercury day is about two-thirds of a year long.

Surface like the moon

Mercury's surface is as bumpy as the moon. Photo: NASA

Mercury's surface is full of large and small craters and is as jagged as the surface of the moon. Most of Mercury's surface is covered with dry lava.

On the surface of this planet, there are many cracks, or giant cliffs that stretch over a large area, looking like giant steps. Of which, the largest step is more than 1,000km long and up to 3km high.

Mercury has more craters on its surface than any other planet in the Solar System. What's unique is that most of these craters are named after famous writers and artists.

"Messenger God" of the Solar System

Hermes in Greek mythology

People have known about Mercury since very early times. In 3,000 BC, the Sumerians already knew about the presence of Mercury. Because Mercury is in the Earth's orbit, when viewed from Earth, it can only be seen at dawn or dusk, not at night.

The Romans named Mercury after the god Mercurius (the Greeks called him Hermes), the mythological god of communication and messenger. Perhaps the Romans named Mercury that way because they noticed its fast speed.

Very difficult to "get used to"

The Messenger satellite completed its mission in 2015. Photo: NASA

Knowledge about Mercury is still limited due to the difficulty in accessing this planet. Up to now, only two probes have "tried" to conquer Mercury: one is Mariner 10 in the period of 1974-1975, the other is Messenger launched into space on August 3, 2004.

As for the Messenger spacecraft, after arriving at Mercury's orbit on March 17, 2011, the spacecraft carried out the mission of observing and researching historical and geological information of the planet closest to the sun.

Messenger flew 7.8 billion kilometers in more than 6 years to reach Mercury and is the first space probe to enter Mercury's orbit.

Messenger orbited Mercury from 2011-2015 and sent back more than 280,000 images to Earth before ending its mission by crashing into the planet.