Historical evolution of asteroids

The discovery of asteroids is closely related to the proposition of Titius-Bode law. According to this law, there should be a planet 2.8 astronomical units away from the sun. 180 1 On New Year's Day, Piacci really discovered the first asteroid ceres there.

180 1, 1 in the evening, Jules Pei Piazi found a star of Taurus at Palermo Observatory in Sicily, which can't be found on the map. At first he thought it wouldn't be another comet. But when its orbit was determined, it was found that it was not a comet, but more like an asteroid. Piazi called it Ceres (Ceres, the goddess of grain and farming, the beauty of Sicily's grain), also known as Ceres. In the following years, Venus, Venus and Vesta with orbits similar to Ceres were discovered one after another. The introduction of astrophotography and the use of flash comparator have greatly improved the annual discovery rate of asteroids. Piazi himself didn't take part in the project of looking for "ghost", but he had heard of it. He suspected that he had found a "ghost", so he continued to observe the star for the next few days. He reported his discovery to the Gotha Observatory, but at first he said that he had found a comet. After that, Piazi became ill and could not continue to observe. It took a long time for his discovery report to reach Gotha. At this time, the star has moved in the direction of the sun and can't be found anymore.

By the19th century, hundreds of asteroids had been discovered. So far, more than 7,000 asteroids have been discovered, and this number is still growing at the rate of several hundred every year. There is no doubt that there must be hundreds of asteroids on the earth that are too small to be observed. As far as we know, there are 26 asteroids with a diameter greater than 200 kilometers. The observation data of these visible asteroids have been basically completed. As far as we know, about 99% asteroids are less than 100 km in diameter. The cataloging of asteroids with diameters ranging from 10 to 100 km has been half completed. But we know that there are some smaller asteroids, and there may be nearly a million asteroids with a diameter of about 1 km. The sum of the masses of all asteroids is less than that of the moon. Photography entered astronomy from 65438 to 0890, which greatly promoted the development of astronomy. Before discovering an asteroid, astronomers must record the position of each suspicious star for a long time and compare their changes with those of the surrounding stars. But on the photographic negative, asteroids moving relative to the stars can be easily determined by pulling a line on the negative. And with the enhancement of the sensitivity of the negative film, it will soon be more sensitive than the human eye, and even darker asteroids can be found. The introduction of photography has greatly increased the number of asteroid discoveries. In 1990, CCD photography technology was introduced. With the improvement of computer analysis electronic photography technology, more asteroids were discovered in a short time. The number of asteroids known today is about 220,000.

After the orbit of an asteroid is determined, astronomers can estimate its size based on the analysis of its brightness and albedo. In order to analyze the albedo of asteroids, astronomers usually use both visible light and infrared light to measure it. However, this method is not very reliable, because the surface structure and composition of each asteroid may be different, so the analysis of albedo often has a large error.

More accurate data can be obtained through radar observation. Astronomers use radio telescopes as high-power generators to emit strong radio waves to asteroids. The distance of asteroids can be calculated by measuring the arrival speed of reflected waves. The analysis of other data (diffraction data) can infer the shape and size of asteroids. In addition, observing the occultation of asteroids can also calculate the size of asteroids more accurately.

By 1940, there are 1564 asteroids permanently numbered. Among them, German astronomers Cohen and Hansen have made great contributions because they are good at orbit calculation, while Wolff and Reinmus have made many discoveries in their observations. Non-manned spaceship Study of Asteroids

Before entering the era of space travel, even under the largest telescope, asteroids were only a point of light the size of a needle tip, so their shape and terrain were still unknown.

197 1 mariner 9 took photos of Fubos and Damos in 2008, which was the first close-up shot of an asteroid.

199 1 years ago, people obtained the data of asteroids through ground observation.

199 1 year, Galileo, a spacecraft heading for Jupiter, flew over 95 1 Gaspar and took the first real close-up of an asteroid. 1993, Galileo flew over actress Ai No.243 and her satellite Dactyl.

1997, the first space program devoted to detecting asteroids was Rendezvous-Shoemaker.

1On June 27th, 997, the near-earth probe passed by the 253 Mathilde asteroid. This rare opportunity enabled scientists to observe this carbon-rich C-type asteroid at close range for the first time. Because the near-earth probe did not specifically investigate it, this visit became the only visit to it so far. NEAR was used to investigate the Eros asteroid in 1999+ 10.

So far, about 700,000 asteroids have been discovered in the solar system, but this may be only a small part of all asteroids, and only a few of these asteroids have a diameter of more than 100 km.

The largest asteroid since 1990 is ceres.

The asteroid data obtained before 199 1 year were only observed on the ground. 199 1 In June, Galileo Jupiter visited asteroid 95 1 Gaspula, thus obtaining the first high-resolution asteroid photo. 1In August, 993, Galileo flew over the asteroid 243 Ida, becoming the second asteroid visited by a spaceship. Gaspra and Ida asteroids are both rich in metals and belong to S-type asteroids.

We have learned a lot about asteroids by analyzing the space junk falling on the earth's surface. Those asteroids that collide with the earth are called meteoroids. When a meteoroid intrudes into our atmosphere at high speed, its surface vaporizes due to the high temperature generated by friction with air, and gives off strong light, which is a meteor. If a meteoroid does not burn completely and falls to the ground, it is called a meteorite.

1999, deep space 1 visited the 9969th head of state.

In 2002, Stardust visited Anne Frank.

Since the 20th century, some asteroids found in the Kuiper Belt have larger diameters than Ceres. For example, the diameter of Varuna discovered in 2000 is 900km, the diameter of Quaoar discovered in 2002 is 1280km, and the diameter of Ercus discovered in 2004 may even reach 1800km. Sedna (asteroid 90377) discovered in 2003 is located outside the Kuiper Belt with a diameter of about 1500 km.

In September, 2005, Ben's spaceship Hayabusa arrived in Sichuan on 25 143 for detailed exploration and may bring back some samples.

The next asteroid exploration plan is Rosetta of the European Space Agency (launched in 2004), and it is expected to explore 2867,20 20 10/0 in 2008. Teins and 2 1 Lutsia.

In 2007, NASA launched the Dawn spacecraft. Astronomers have made ground observations on many asteroids. Some famous asteroids are Toutais, Castalia, Vesta and Geographos. For asteroids Toutatis, Castalia and Geographos, astronomers study them by radio observation on the ground when they are close to the sun. Vesta asteroid discovered by Hubble Space Telescope.