The collision danger of Apophis

The Turin hazard index of Apophis asteroid reached level 4 in 2004, and then decreased to 1. After 2006, the risk index of Turin remained at 0. The Apophis asteroid was discovered at 20 12, with a width of more than two football fields and a width of 400 meters. Because it is possible to hit the earth in the relatively near future, it has attracted much attention from scientists in recent years. Scientists once thought that if Apophis hit the earth, it would not lead to global destruction, but it might cause serious regional disasters.

Scientists held an expert meeting on "Near-Earth Objects" in London, England, to discuss the method of "saving the earth at the end of the day". Monica Grady, a meteorite expert from the Open University of the United Kingdom, said: "It is only a matter of time before a near-earth asteroid collides with the earth, not whether it will happen. Many smaller space objects melted when they rushed into the earth's atmosphere, so they failed to collide with the earth. Asteroids with a diameter greater than 1 km will collide with the earth every few hundred thousand years, and asteroids with a diameter greater than 6 km will collide with the earth every few hundred million years. Such an impact will lead to extinction. This time, human beings are faced with a big guy who is late. "

Some scientists estimate that the asteroid 99942 (Apophis) has a 2.7% chance (1/37) of hitting the Earth in 2029. Further observation and re-estimation of its orbit have ruled out the possibility of it hitting the earth in 2029, but it is determined that it may change its orbit through a gravity keyhole with a width of about 6 10 m in 2029, which may lead to Apophis hitting the earth in 2036. In recent years, it is estimated that the probability of Apophis hitting the earth in 2036 is1/250,000 (0.0004%) [2]. Apophis is about 400 meters long. If it hits the earth, it may cause millions of casualties.

Scientists from the B6 12 Foundation, a private organization dedicated to preventing the earth from being hit by celestial bodies, suggest that Apophis' orbit may move from its current orbit to a position farther away from the gravity keyhole. David Morrison, a NASA scientist, said: "After 2029, Apophis' orbit deviation must be large enough to miss a small range of gravity keyhole, even the earth with a much larger gravity keyhole. The technology of making an Apophis-sized asteroid biased enough is far beyond the current human ability. " [3]

Further observation and analysis show that Apophis may have missed the gravity keyhole. As of June 10 and June 19, 2006, the probability of Apophis hitting the earth on April 13, 2036 is 1/45000. Another possible date to hit the earth is 2037, which has been confirmed, and the estimated impact probability is11230000.

Gravity keyhole space size

Apophis's gravitational keyhole is only 6 10 meter in diameter. The calculation shows that if Apophis' speed can be changed by 0.000 1 mile, its orbit will deviate more than 1 mile, which is enough to miss the gravity keyhole in the next three years. The problem is that the gravitational keyhole is too small to accurately predict whether Apophis will pass. The orbit calculation in 2006 shows that the orbit prediction error of Apophis in 2029 is about 3200 kilometers; In the early estimate of 20 10, Apophis will be 18600 miles away from the earth in 2029, and the gravity keyhole will be 18893 miles away from the earth. As time goes by, the error ellipse of orbit estimation will gradually decrease, but NASA may have to accumulate enough data to know whether Apophis will pass through the gravity keyhole until the error ellipse can be reduced to less than 1.6 km. [4] Hawking, a famous British theoretical physicist and mathematician, pointed out that due to the threat of near-earth small objects, human beings must emigrate to other planets suitable for survival in order to get rid of the fate of extinction. At present, the near-earth asteroid that poses the greatest threat to the earth is the Apophis asteroid, which will "pass by" the earth in 2029; If the Apophis asteroid passes through the gravitational eye above the Earth with a probability of one in 370,000 (gravity is only one quarter of the normal value), it will be dragged into the orbit around the Earth, and in 2036, seven years later, it will enter the atmosphere from the North Pole, pass through the Siberian Plain, pass through big cities such as new york, and circle the Earth, and eventually fall into a place in North Africa, which is the highest risk level among small celestial bodies discovered so far.

Since 1990s, scientists have held various relevant international academic seminars every year to discuss countermeasures. At present, NASA, the European Space Agency and some related agencies are strengthening the monitoring and tracking of small celestial bodies that are most likely to endanger the earth. Space "clairvoyance"-Hubble telescope is also constantly monitoring their "activities". American researchers pointed out that it is extremely unlikely that an asteroid will hit the earth at that time.

Donald yeomans, head of the Near-Earth Object Project Office of NASA, told the media that from the perspective of natural probability, the probability that an Apophis asteroid will hit the Earth in 2036 is only one in 250,000. The reason why this probability is so small is that if the asteroid Apophis wants to enter the orbit of colliding with the earth, it must pass through the "gravitational keyhole" area of near-earth space, and then it may collide with the earth under the action of the gravity of the earth. However, the diameter of this asteroid is more than 300 meters, which is much smaller than that of the "gravitational keyhole". It is extremely unlikely that the high-speed flying "Apophis" asteroid will fall into the "gravitational keyhole".

Yeomans also pointed out that with the science and technology mastered by human beings, experts will not wait until 2036 when asteroids threaten the earth before taking countermeasures.

Yeomans said that the more realistic prospect is that when the Apophis asteroid flies through the Earth from 20 12 to 20 13, astronomers will make a detailed analysis of its orbit with various space telescopes and ground observation facilities, and then experts can draw a conclusion whether the asteroid may collide with the Earth. If there is a high possibility of collision, NASA can also push the asteroid out of the orbit that collides with the earth. A simpler way is to launch a spaceship and crash an asteroid into an orbit far away from the earth.

On July 4th, 2004, the American Deep Impact Detector successfully bombarded the Temple 1 comet with an impactor. Yeomans believes that this bombardment test is a very useful attempt to prevent asteroids from threatening the earth.