There are currently 8 planets in the solar system. The closest to the Sun and the smallest is Mercury. It is customary to refer it to the terrestrial planets, which include Mars, Venus and Earth.
History and hypotheses
Astronomers discovered Mercury in antiquity, but they believed that in the evening and in the morning they observe two different "stars", and not the same one. Mercury got its name in honor of the ancient Roman god who was the patron saint of commerce, thieves and travelers.
Mercury can be seen with the naked eye in the morning just before sunrise and in the evening after sunset. Mercury is the closest planet to the Sun, so it is quite difficult to observe it. In the terrestrial sky from the Sun, it departs a maximum of 29 °.
Currently, there is an interesting hypothesis that Mercury is a very long-lost satellite of Venus. Mathematical modeling has shown that this option is not excluded, moreover, it can explain the rather strange "slowed down" axial rotation of both planets. Unfortunately, to confirm the hypothesis, detailed studies are required, which are currently impossible.
Mercury (after Pluto was stripped of planetary status) is the smallest planet in the solar system. Its radius is 2440 km, and the average distance from the Sun is 58 million km. The mass of this celestial body is actually 20 times less than that of the earth, it should be noted that Mercury is much smaller than some of the satellites of Saturn and Jupiter. He himself does not have companions.
The atmosphere of Mercury is created by the solar wind, it is very rarefied and consists of helium. At the very surface of Mercury, the pressure of this atmosphere is 500 billion times less than the normal air pressure on Earth. The maximum temperature on the illuminated side of Mercury reaches 430 ° C, while on the dark side of the planet, the temperature can drop to -170 ° C. Interestingly, such strong temperature changes do not penetrate deeply under the surface of the planet, since its outer layer is very highly crushed and works as an excellent thermal insulation. At a depth of only a few tens of centimeters, the temperature is constantly kept at 80 ° C.
Mercury has a very elongated orbit. For example, the distance from Mercury to Earth can range from 82 to 217 million km. At the same time, Mercury moves in its orbit faster than other planets, the average speed of this movement is 48 km / s, and it makes a complete revolution around the Sun in 88 usual Earth days. Surprisingly, Mercury's daily rotation is one of the slowest among all the planets. It turns around its axis in 2/3 of the Mercurian year or in 58.6 Earth days.