What is the true face of Mercury?

Usually, it is difficult for people to see mercury, which is mainly related to the angle between mercury and the sun. Mercury is 69 million kilometers farthest from the sun and 45 million kilometers nearest. Seen from the earth, its included angle with the sun does not exceed 28 degrees, and Mercury always seems to swing on both sides of the sun. Therefore, Mercury is almost always "submerged" in the brilliance of the sun at dusk or dawn. You can only see it near 28 degrees.

Mercury was called the "morning star" in ancient China. Mercury travels very fast around the sun, about 48 kilometers per second. It only takes 88 days to go around the sun. Astronomers have long believed that its rotation period is 88 days, which is as long as that of period of revolution.

Although some people have doubted the rotation period of Mercury, people still don't know the exact rotation period of Mercury because of instruments and technology. With the improvement of astronomical observation level and instrument accuracy, the rotation period of Mercury was finally measured. 1965, American astronomers used the radio telescope of Arecibo Observatory to emit radar waves to detect Mercury. This is the largest radio telescope in the world (305 meters in diameter). It measured the exact rotation period of Mercury as 58.646 days. It turns out that Mercury revolves around the sun twice and rotates around the earth's axis three times, so the rotation period of Mercury is exactly two-thirds of that of period of revolution.

Since then, scientists have carried out more in-depth exploration and research on Mercury, but even the best telescope on the earth at that time, it is difficult for people to see the surface of Shimizu. As a result, scientists adopted the high-end tool of planetary probe. The United States launched the "mariner 10" planetary probe on June 3, 18. This is the only spacecraft that has visited Mercury so far. The main mission of this launch is to explore Mercury and visit Venus. The total weight of "Mariner 10" is about 528kg, and the width from the top of the magnetometer to the outer edge of the parabolic antenna is 9.8m m. After more than three months of flight, the spacecraft flew over Venus on February 5, 1974, only 5,000 kilometers away from Venus. When inspecting Venus, the spacecraft changed its speed and direction under the "support" of Venus' gravity, entered an orbit flying to Mercury, and finally reached the sky above Mercury on March 29th.

Space scientists carefully designed the orbit of the spacecraft. When it reaches the sky above Mercury and observes it, it becomes an artificial planet orbiting the sun. Its cycle around the sun is designed to be twice as long as the period of revolution of Mercury, that is, 176 days. In this way, when Mercury had just circled twice, the spacecraft met Mercury once. "Mariner 10" spacecraft has met Mercury three times and obtained a number of high-quality photos. Its camera lens can clearly distinguish the details of the ground structure on the surface of Mercury, that is,1200m.

By analyzing the feedback data of spacecraft, scientists found that the surface of Mercury was covered with numerous craters, uneven basins and potholes of different sizes. Some craters show that meteorites hit the same place many times, which is very similar to the surface of the moon. The difference between the surface of mercury and the surface of the moon is that there are not many craters with a diameter of 20 ~ 50 km, while there are many craters with a diameter of more than 100 km on the surface of the moon. There are some fan-shaped cliffs called "tongue cliffs" everywhere on the surface of Mercury, which are 1 ~ 2km high and hundreds of kilometers long. Scientists believe that they are actually huge folds formed by the shell of early mercury when its huge core cooled and contracted. There is a Grand Canyon on Mercury, which is more than 100 kilometers long and about 7 kilometers wide. Scientists named it "Arecibo Canyon" to commemorate the fact that arecibo radio telescope measured the rotation period of Mercury.

Scientists also found that the temperature difference between the front and back of Mercury is very large. Because there is no atmosphere, it is directly attacked by solar radiation. Under the sun's baking, the sun-facing temperature of Mercury is as high as 427℃, and the back-facing temperature is as cold as-170℃. There is no water on the surface of mercury. Mercury's mass is less than that of the earth, and its gravity is only 3/8 of that of the earth, so as long as the speed reaches 4.2 km/s, objects on its surface can escape.

The Mariner 10 spacecraft detected that Mercury not only has a magnetic field, but also has a global magnetic field with a strength of about1100. The discovery of mercury's magnetic field shows that there is probably a high-temperature liquid metal core inside it. According to the mass and density of Mercury, scientists have calculated that it should have a heavy and large iron-nickel core, which is about 2/3 of the diameter of Mercury.

With the development of space technology in the world, scientists will continue to increase the detection of mercury, and one day, the true face of mercury will be presented to the people on earth.