The smallest planet in the world

The smallest planet in the world is Mercury.

Mercury was called Mercury in ancient Europe because of its fast movement. In ancient Roman mythology, it means the messenger god running at full speed. China was called Chen Xing in ancient times, which was recorded in the history books of the Western Han Dynasty? Sima Qian, the author of Tian Guan Shu, found that Chen Xing was gray from practical observation, which was related to the theory of five elements. Black belongs to water and is named Mercury. Mercury is the smallest of the eight planets in the solar system and the closest planet to the sun. The orbital period is 87.969 1 day, and it meets the earth once every 6 days, and the revolution speed is far faster than other planets in the solar system.

Mercury is the planet with the largest temperature difference between day and night, and its atmosphere is extremely thin, so it can't effectively store heat. The temperature in the equatorial region can reach 437℃ during the day and drop to-172℃ at night ... The axis inclination of Mercury is the smallest among all planets in the solar system (about 1? 30 degrees), but it has the largest track eccentricity. The distance of Mercury at apohelion is about 1.5 times that of perihelion. The surface of mercury is covered with craters, similar to the moon and other satellites, and its geology has been inactive for billions of years.

Structure principle of mercury material density;

Mercury is one of the four terrestrial planets in the solar system, and it has the same rock body as the earth. With a radius of 2439.7 kilometers, the equator is the smallest planet in the solar system. Mercury is even smaller than some giant natural satellites, such as Ganymede and Titan, although it is heavier. Mercury consists of about 70% metal and 30% silicate material. The density of Mercury is 5.427g/cm3, which is the second highest density in the solar system, second only to the earth's 5.5 15g/cm3.

The density of mercury will be the highest if the influence of gravity compression on the density of matter is not considered. In the absence of gravity compression, the density of mercury is 5.3 g/cm3, while the density of earth material is 4.4 g/cm3. From the density of mercury, we can infer the details of its internal structure. The high density of the earth, especially the high density of the core, is caused by gravity compression. Mercury's mass and gravity are very small, there is no gravity squeezing effect inside, and its core contains a lot of iron with high density.

Geologists estimate that the core of Mercury occupies 42% of the volume; The core only accounts for 17% of the volume. Mercury's iron-rich core accounts for at least 60% of its total mass, and its radius is three-quarters of that of Mercury. Recent research strongly supports that Mercury has a molten core surrounded by a silicate mantle 500-700 km thick. Of the planets in the solar system, only Mercury and Earth have global magnetic fields. Astronomers believe that these magnetic fields are generated by the current in the outer layer of the earth's core.

According to Mariner 10 and the data observed from the earth, the crust of mercury is considered to be only 100-300 km thick. A major feature of the surface of Mercury is that there are numerous narrow ridges, which can extend to hundreds of kilometers. It is believed that after the shell of Mercury solidifies, the core and mantle will shrink due to cooling.

Reference to the above content: Baidu Encyclopedia-Mercury