As Pluto is removed from the solar system planets, Mercury becomes the smallest of the eight planets in the solar system, measuring approximately 4,880 kilometers in diameter. Mercury is not even as large as some satellites, such as Ganymede and Titan, which are larger than Mercury. But the quality of Mercury is still greater than their quality, because Mercury has a higher density, second only to the Earth. If the effect of gravity compression on material density is not considered, the density of Mercury material will be the highest in the solar system.
The planet closest to the sun
The average distance between Mercury and the Sun is 57.91 million kilometers, which is about 0.387 times the distance between the Sun and the Earth. Because it is too close to the sun, it is always annihilated by the radiance of the sun, so Mercury is the most difficult to observe in the solar system. Only when the angular distance between Mercury and the Sun reaches its maximum or large distance, the talents on Earth are expected to see Mercury. When Mercury is “eastward”, it can be found on the western horizon at dusk; when Mercury is “westward”, it appears at low altitude in the east at dawn; there is also an opportunity to observe Mercury at the eclipse.
Planet with the fewest satellites
Mercury is the same as Venus, and the number of satellites is “zero.” The main reason is that the quality mentioned above is too small and too close to the sun. According to the principle of gravity, objects of too small a mass cannot form enough gravitational force. Even if there is a satellite, it will be taken away by the strong attraction of the sun.
The fastest planet in the revolution
Because Mercury is close to the sun, it is also attracted by the sun, so it runs faster than other planets in orbit around the sun. Earth revolution takes about 365 days a week, while Mercury only uses 88 days. However, Mercury’s rotation period is very long, at 58.65 days. In other words, a Mercury year is only a day and a half.
Planet with the largest surface temperature difference
Because Mercury’s atmosphere is extremely thin, it can’t effectively save heat, and it is close to the sun, so the temperature difference between the surface of Mercury and the moon is extremely large. The sun’s side is battered by the sun, the temperature in the equatorial region can reach 430 ° C; the side facing away from the sun can be reduced to -170 ° C, the temperature difference is up to 600 ° C, the highest in the solar system. In contrast, Venus has a strong atmosphere, and although the surface temperature is higher than that of Mercury, the temperature difference is not too great.
Planet visited by at least human detectors
The absolute distance between Mercury and the Earth is not far away, but it is more difficult to launch a Mercury detector by Homan transfer (by transferring the orbit of the spacecraft and using the energy generated by the gravitational force of the star to save fuel), but it is more difficult than launching the Pluto detector. Don’t say that you are surrounded by Mercury. Prior to “Bepicolombo”, only two detectors in the United States detected Mercury. The first detector to visit Mercury was the “Sailor 10” launched on November 3, 1973. In the process of meeting with Mercury three times, more than 5,000 photos were sent back to the ground, providing us with valuable information about Mercury.
Mercury looks like the moon, with many craters of varying sizes, as well as radiation, plains, rift valleys, and basins. The second is the Mercury Detector, which was launched on August 3, 2004. It is also the first detector to orbit Mercury. On April 30, 2015, the “Messenger” ended its mission by hitting Mercury.
“Bipic Colombo” will study the structure of Mercury’s internal structure and magnetic field to determine whether the core of Mercury is solid or liquid, and explore the origin and evolution of Mercury, thus helping us to better understand the overall evolution history of the solar system.