When did the comet impact happen?

Up to now, the celestial impact event that astronomers have made accurate predictions and made detailed observation in the whole process was the collision between comet S-L9 and Jupiter in July 1994.

During the week from July 16th, 1994, astronomers and amateur astronomers all over the world observed the serial collision of comet Shoemaker-Levy 9 (S-L9 for short) with Jupiter. This once-in-a-lifetime astronomical event has aroused the deep concern of scientists, because it has brought the study of comets, asteroids hitting the earth and Jupiter into a new stage.

comet s-l9 is a periodic comet discovered by the famous American "comet hunters" Sumek and Levy. Eugene Shoemaker, born in 1928, was the head of astronomy department of USGS, when he just retired. For more than 2 years, he has been engaged in the search for new comets and asteroids, and won the National Science Award in 1991. His wife, Caroline, who is two years younger than him, is a self-taught astronomer. In 1982, she joined her husband's astronomical observation work without compensation, and their two children have grown up at this time. Caroline is as careful as silk, and can often notice irregular and tiny spots from astronomical negatives, thus discovering new comets. She discovered 32 new comets, which is still a personal world record.

At midnight on March 23rd, 1993, the like-minded couple searched for comets with amateur astronomer David Levy who assisted them in their work. Two days before that, the weather was bad and the clouds were thick. They saw almost nothing. They used the 45-centimeter telescope of Paloma Mountain Observatory in California, USA, and took some photos at random towards Jupiter. Levy, born in 1948, owns an astronomical telescope with a diameter of 2 cm. He has discovered 8 comets alone and 13 comets in cooperation with others. That night, the few photographic negatives they had left were slightly "gone", and the shooting effect was expected to be difficult to guarantee. Only at the insistence of the optimistic Levi, the Sumeks took a few photos at will.

When putting the developed negative under a stereo microscope, Caroline noticed that the edge of the negative was only slightly blurred due to light leakage. Carefully, she found a string-shaped celestial body in an area near Jupiter on the negative, which was obviously different from the usual point-shaped celestial body. She described: "It appears in the form of dim lines with a dense tail, which looks like a crushed comet." The three collaborators discussed this phenomenon for nearly an hour, and finally convinced that it was a newly discovered comet, not an asteroid.

Then, Levy sat down in front of the computer and sent an email to Marsden, the head of the Astronomical Telegraph Bureau under the International Astronomical Union, through the computer network, asking to verify their findings. Soon, Levy also called the astronomer Scott of the University of Arizona and asked him to observe and verify the sky near Jupiter. As a result, their findings were quickly confirmed by Scott's clearer CCD images. Fifteen minutes later, Scott and Levy confirmed on the phone that they had observed a comet. So Scott immediately wrote a letter to marsden, confirming that the Sumeks and Levy were the discoverers of this new comet, and the comet fragments showed a string distribution.

Later, it was learned that three astronomical observation teams in Japan, Chile and California had also observed this astronomical phenomenon within a few days before Sumek and the three of them discovered this comet, but they didn't go further and missed a good opportunity to discover a new comet. In recognition of the contributions of Shoemaker and Levy, the international astronomical organization named the comet after them, which is the "S-L9" comet that attracted worldwide attention in this century.

after analyzing the orbit of comet S-L9, astronomers think that this comet is not orbiting the sun like most other comets, but orbiting Jupiter. It was probably originally a small satellite of Jupiter, or a member of the asteroid in the Tuoluoyang Group, and it is rich in volatile substances. Some scholars speculate that it may be an ordinary comet captured by Jupiter.

It is estimated that comet S-L9 was only 43, kilometers away from Jupiter on July 8, 1991. Because it was too close to Jupiter, it was torn and disintegrated by the tidal force generated by Jupiter's strong gravity, and became a series of fragments. According to 156 observations of comet S-L9 in four months before and after its discovery, American astronomers yeomans and Jordas calculated its orbit, and predicted that these separated comet nuclei would collide with Jupiter again in mid-July, 1994, with at least a 99% chance. Later, on the basis of further research and calculation, a very exciting and accurate prediction was finally obtained: that a series of comet fragments will crash into Jupiter's atmosphere one after another in a few days from July 16 to 24, and trigger a rapid-fire fireball explosion in the depths of the clouds. In the history of modern astronomy, it is a mature business to calculate the orbit of celestial bodies according to their observed displacements. On July 1, 1993, the Hubble Space Telescope, which was running in space, took a clearer picture of comet S-L9, which clearly showed that each comet fragment was surrounded by spherical dust clouds, and it was estimated that the diameter of any single fragment would not exceed 4 kilometers. From October 18 to 22, 1993, a special conference was held in Colorado, USA, at which some astrophysicists made bold predictions.

According to the astronomers' forecast, the comet debris landed on the dark side that marks the dividing line between day and night of Jupiter, that is, the initial scene of the impact could not be directly observed on the earth at that time, but people could see the flash caused by the impact explosion on Jupiter's satellite, and they could also carefully observe all kinds of scars caused by the impact, as well as the explosion jet-mushroom cloud emerging from Jupiter's edge. The first comet nucleus (about 1 km in diameter) hit Jupiter at 2: 15 GMT on 16th (4: 15 am Beijing time on 17th). Then, at intervals of about 7 hours, 4 hours, 6 hours, 2 minutes and 4 hours respectively, the other four comet nuclei also collided with Jupiter.

The data collected by the American Space Telescope Science Institute and NASA Goddard Space Flight Center from space and ground telescopes show that many fireballs produced after the first impact stretch for nearly 1 kilometers. Theoretical calculation shows that the speed of the comet nucleus containing rocks and ice blocks hitting Jupiter is as high as 21, kilometers per hour, which can cause a strong shock wave in the upper atmosphere of Jupiter, and may penetrate the clouds composed of ammonia and the dense hydrogen layer below several kilometers, so that the temperature in some areas of the splash point will instantly rise to tens of thousands of degrees Celsius.

according to Japanese news media reports, the first fractured comet nucleus (block A) formed a huge mushroom cloud when it hit Jupiter, and the high-temperature gas rushed to a height of 1, kilometers, leaving a black spot on the surface of Jupiter as big as the earth. On the day after the first impact, NASA held a press conference, which was attended by Shoemaker, his wife Caroline and Levy, and answered questions that journalists were interested in. Sumek said that the comet fragments crashed into Jupiter's atmosphere, causing Jupiter to emit hot gas and rush into space. The spectacular wonders of the cloud cluster were very beautiful. Although the collision occurred at the southern end of Jupiter's back, it could not be directly observed from the earth, but because Jupiter rotates very fast, the ground observatory can see the changes of Jupiter's cloud in about ten minutes. The diameter of comet fragment A is between .8 km and 1.6 km, and the energy of hitting Jupiter is equivalent to 2 billion tons of dynamite.

At 7: 3am GMT (3: 3pm Beijing time) on 18th, the seventh comet fragment hit Jupiter, and its "scar" on Jupiter was observed by Nanjing Purple Mountain Observatory at 7: 3pm GMT. It is a "crater" with a diameter of 2, kilometers, located at 44 19' south latitude of Jupiter, which is basically consistent with the location predicted in advance.

According to American astronomer Mullen, at 1: 2 on the 19th (6: 2 pm Beijing time on the 19th), the fireball produced by the 9th fragment that hit Jupiter had the same brightness as that produced by the 7th fragment. He pointed out that it was in 161 that humans first observed Jupiter with a newly invented telescope. According to historical astronomical data, its appearance has not changed much since then.

A raised paraboloid composed of dust clouds appeared above the impact point of the seventh comet fragment, and there was a circle inside the paraboloid. This appearance was figuratively compared to an "eye" by astronomers, and it immediately became the most prominent identification sign of Jupiter. Mcfadden, an American female astronomer, reported that the trace of Jupiter caused by the seventh fragment is so obvious that even amateurs can observe it in the clear night sky with ordinary small-caliber telescopes.

At 18: 12 and 22 pm (Beijing time) on the 2th, two pieces of comet S-L9' s comet nucleus hit Jupiter again. Between 23: 11 and 12: that night, another comet nucleus hit Jupiter, which was the 13th collision since the early morning of the 17th. At that time, astronomers said that Jupiter's southern hemisphere had been scarred by S-L9' s fierce "attack" for more than 1 times in a row. Seven large wounds were more than 1, kilometers in diameter, and one wound was estimated to be tens of thousands of kilometers in diameter, which greatly exceeded the earth's volume. An observation report provided by Mr. Fu Chengqi, the chief scientist of the S-L9 comet project of Shanghai Observatory, said that due to the repeated bombardment of Jupiter by comets, the time for the atmospheric circulation to rotate around 45 south latitude of Jupiter was shortened by about 45 minutes. Considering Jupiter's huge size, it is roughly estimated that the speed of storms in Jupiter's atmosphere due to impact reaches 1 meters to 15 meters per second.

The Beijing Observatory and 22 institutes of the Ministry of Electronic Industry jointly observed a strong radio burst caused by the impact of the No.15 comet nucleus on Jupiter's magnetosphere in Xinxiang, Henan Province. In the 25 MHz band, its intensity was 1, times greater than the background intensity. From 18: 24 to 29: on the 19th, an electric wave burst caused by the impact of No.12 comet nucleus on Jupiter was observed in the 29 MHz band, and the intensity was enhanced by about 5 times. From 21: to 22: on the 18th, with a 6-centimeter telescope, Xinglong Observatory of Beijing Observatory observed about 4, kilometers of dark spots at the impact point of No.17 comet nucleus on Jupiter's surface, and at the same time, with a 2.16-meter telescope, it was observed that the spectrum of the impact point changed obviously from 6,64 to 6,66 angstroms.

The last fragment of comet S-L9 hit Jupiter shortly after 8: GMT on July 22nd (4: pm Beijing time on July 22nd). The information transmitted by two astronomers from the University of Chicago in the United States through the computer network confirmed that they observed that the fireball generated by the impact of the last fragment (the 21st fragment) of S-L9 on Jupiter was not as bright as other fragments before it. Sugek said at a news conference on the eve of the last comet fragment hitting Jupiter: Comet S-L9 was originally about 1 kilometers in diameter, with a mass of about 5 billion tons, and there were at least 21 fragments split by the comet. The debris falls to Jupiter at a speed of about 21, kilometers per hour, and the total energy released is equivalent to the energy generated by 4 trillion tons of TNT explosion, and the instantaneous high temperature may be close to 3,℃.

Scientists took advantage of this comet-wood collision to analyze the chemical composition of the atmosphere of comet S-L9 and Jupiter. They have found sodium, sulfur, nitrogen, hydrogen sulfide, hydrogen cyanide and trace moisture. In observing the collision between comets and trees, astronomers found ammonia gas above the impact point, but did not find the expected large amount of water vapor. This makes people have a question: Is S-L9 a comet? If it's not a comet, why is there a tail? And why did it disintegrate into 21 pieces?

mcfadden of the United States believes that finding water is the key to understanding Jupiter's atmosphere. People had expected to see bright white clouds when each fragment hit Jupiter, but the observable situation did not match the idea that people expected to find water. Some scholars therefore suspect that S-L9 is not a real comet. Comets are generally composed of gas, ice and dust, and often come from the edge of the solar system. Its distinctive feature is that it "grows" its tail when it approaches the sun. Asteroids, on the other hand, are big stones and run in the inner solar system. It is generally believed that they have no water. Mcfadden said that it may also be that the existing instruments are not accurate enough to detect water.

The fireball generated by this collision led to the formation of charged particle mixture, which emitted powerful radio signals when rotating with Jupiter's magnetic field. The flash phenomenon caused by collision also makes it possible for scientists to carry out chemical analysis, but it will take some time to determine which compounds come from comets, which come from Jupiter's atmosphere and which are produced by fireballs. By observing how the dark spots on Jupiter finally disappear, it is possible to get more information about Jupiter's climate and wind direction. The collision of comets and trees also produced a huge shock wave on Jupiter, which covers nearly a quarter of Jupiter's area and moves at a speed of about 734 meters per second. American astronomer Laney said that the observation results showed that the comet fragments could not penetrate deep into Jupiter's atmosphere and liquid hydrogen layer. He said that when comet fragments hit Jupiter at a speed of 6 kilometers per second, they were blocked by Jupiter's thick atmosphere.

After comet S-L9 hit Jupiter, people have to pay more attention to these comets and asteroids that will pose a threat to the earth. According to astronomers' estimation, there are about 2, comets and asteroids that pose a threat to the earth at present, because their orbits may coincide with the orbits of the earth. But it is estimated that only about 1 can be found in time. In August 1994, NASA began to classify and catalogue comets and asteroids with a diameter of more than 1 km, which may collide with the earth, so that scientists can find and track these uninvited guests in time and protect the beautiful home of mankind. 4. Constellation explosion that created 1, Earths

On January 7th, 23, a rare Supergiant star named "RhoCas" which was 1, light years away experienced a large-scale explosion. Astronomers say that the debris produced by this explosion is enough to create 1 thousand "earths"