According to common sense, mercury is closest to the sun, but why is it 5 degrees Celsius during the day and MINUS 15 degrees Celsius at night? Why is it so cold?

The average surface temperature of Mercury is about 452K, ranging from 9 K to 7 K. It is the planet with the largest temperature difference. During the day, the temperature in the direct sunlight is as high as 427℃, and when the sun is not shining at night, the temperature drops to -173℃. The temperature difference is so wide that there can be no living things. Can compare the earth, the temperature change on the earth is only 11K (here is only the solar radiation energy, regardless of "season" and "weather"). The sunshine on the surface of Mercury is 8.9 times stronger than that on the Earth, with a total irradiance of 9126.6W/㎡. Surprisingly, radar observations made in 1992 showed that there was ice at the North Pole of Mercury. It is generally believed that the ice exists at the bottom of the crater where the sun can never shine, and it is accumulated due to the impact of comets or the gas coming out of the surface inside the planet. Because there is no atmospheric regulation, the temperature in these places has been maintained at MINUS 28 degrees Fahrenheit (about-173 degrees Celsius).

The surface of Mercury shows huge steep slopes, some of which are several hundred kilometers long and three thousand meters high. Some lie across the outer ring of the crater, while others are formed by compression because of their steep slopes. It is estimated that the surface of Mercury has shrunk by about .1% (or decreased by about 1 km in the radius of the planet)!