In the same solar system, Jupiter has a large number of satellites. Why does Mercury have no satellites around?

There is such a phenomenon in the solar system. Mercury and Venus, the two closest planets to the sun, have no satellites, while the earth has one satellite, Mars has two satellites, and Jupiter has more than 60 satellites. Saturn, Uranus, and Neptune also have satellites. Both have many moons, so why do neither Mercury nor Venus have moons?

This is because they are so close to the sun. In fact, there is also such a phenomenon in planetary systems, that is, the satellites of planets usually do not have satellites anymore. It is also because the satellites of planets are usually too close to the planet, so when a satellite captures an asteroid or a comet as its own satellite , its orbit is usually very unstable due to the great influence of the planet. After the asteroid or comet revolves around the satellite for a period of time, most of it will be captured by the planet, and some will be thrown out by the planet's gravity, so we see that the planet has The moons revolve, but the moons usually have no moons to revolve around, such as Ganymede and Titan, which are larger than Mercury and Pluto, but have no moons, precisely because they are so close to the planets, even if captured A satellite will soon be attracted by Jupiter and Saturn.

So why does the earth have the moon, the moon? The moon has been revolving around the earth for hundreds of millions of years. This is precisely because the moon is in the range dominated by the earth's gravity. Because the mass of the earth is large enough, the earth is relatively more in control, and the earth-moon system is far enough away from the sun. So far The moon is still revolving around the earth, but in billions of years, the moon is actually moving away from the earth. It is estimated that its distance is at least twice as far as it was a billion years ago. Gravity matters.

According to the observations of some astronomers in history, Venus actually once had a satellite. Joe Cassini, the famous French astronomer and the first director of the Paris Observatory, announced in August 1686 that he had discovered the vicinity of Venus. There is a huge unidentified object, which he considered to be a satellite after many observations, and he also determined some values ​​of this satellite. According to his published data, the diameter of the satellite he found was 1,500 kilometers. Slightly smaller than the moon, 1/4 the diameter of Venus, but this moon is closer to Venus than the moon is to Earth.

Cassini is a very rigorous astronomer. The famous Saturn probe launched by the United States was named "Cassini", because he saw the cracks in Saturn's rings first, so those cracks are also called "Cassini". For the "Cassini Ring Slit", with such detailed and precise observations, it is certainly not a problem to be able to see the moons of Venus. Therefore, some scientists at that time and later believed that his observations were more credible, and he had discovered 9 satellites at that time, so the discovery of this Venus satellite was even more sensational.

In fact, it was not only Cassini who saw it. An astronomer named Montani also observed the Venus satellite many times in 1671, and left many detailed records, but the more detailed observations were made by Germany. The mathematician Lampit, who also recalculated the orbit of the Venusian satellite, believed that its orbital radius was 400,000 kilometers, which was slightly larger than the distance between the moon and the earth (a change compared with Cassini's observations), and the orbit around Venus. The period is 11 days and 5 hours, and in 1740, 28 years after Cassini's death, Shorter, an expert in making telescopes in England, also announced that he had seen the moons of Venus.

But the strange thing is that Galileo, who was earlier than Cassini and others, did not discover the satellite of Venus, so the satellite seems to suddenly appear next to Venus, and then disappear after orbiting Venus for decades, because from the After 1768, no one has seen this mysterious planet again. Since Cassini discovered it, it has existed in people's observations for 80 years, and then disappeared without a trace, becoming an unsolved mystery in astronomy.

After this thing disappeared, people became more curious, so where did this thing come from? There are only two possibilities, that is, an alien spacecraft or a planet in the solar system. At that time, people thought it was an alien spacecraft, because people believed that satellites, like the moon, orbit the earth all the time and will not disappear in a short time.

But later, more people thought that it was more likely to be a celestial celestial body. Because it was captured by the gravity of Venus, it revolved around Venus for more than 80 years. The biggest reason for its departure was that Venus was too close to the sun, and its satellites The influence of the gravity of the sun is stronger, so the orbit keeps changing, and the distance from Venus is getting farther and farther in the process of revolving around Venus. When it reaches a certain level, it will break away from the gravity of Venus and be sucked by the sun or run into space. Wandered in the middle, so this statement is also the best comment on the moons of Venus.