Galileo spacecraft passed through the asteroid belt on the way to Jupiter, and photographed the asteroid Ada having a small satellite of its own. Ida is a kind of potato, about 56 kilometers long. At a distance of about 100 km, there is a rock block with a diameter of about 1.5 km, which is the smallest natural satellite in the known solar system. Some asteroids also have their own moons.
Asteroids run in space, because their mass is too small, they are easily influenced by the gravity of big planets (this is called perturbation in astronomy), thus changing their running direction. If the near-earth asteroid deviates from its original orbit and faces the earth after being disturbed, it may collide with the earth and bring great disaster to the earth. It is estimated that there are about 500 near-earth asteroids with a diameter of 0.7∽ 1.5 km, of which about 1000 are smaller. They do pose a potential threat to the earth. In the long years since its birth, the earth has suffered many impacts, leaving traces on the surface or strata, and some even caused serious consequences.
There are some asteroids whose orbits almost constantly cross the Earth's orbit. There are 9 1 asteroid. They are called Apollo asteroids. Astronomers are doing their best to search for such asteroids, in part because they are afraid that they may collide with the earth. Knowing the existence of such asteroids and calculating their orbits, it is possible to find a way to change their orbits and keep them away from the earth. Collisions between the earth and large asteroids are rare, but collisions with small asteroids are more common. It is estimated that several asteroids with a diameter of 654.38+0,000 meters may collide with the Earth after 654.38+0,000 years. If a planet of this size hits the earth, the explosive force is equivalent to several hydrogen bombs, and the collision will form a crater with a diameter of about 13 km, which will also cause short-term global climate imbalance. If the impact point is in the ocean, it will also have disastrous consequences. Some scientists believe that at the end of the Cretaceous period (65 million years ago), an asteroid or meteorite with a diameter of about 10 km hit the northern Yucatan Peninsula, causing the extinction of dinosaurs and many other animals. Asteroids, like meteorites, are composed of different proportions of stony and metallic substances (mainly iron). Many of these celestial bodies contain a lot of carbon, so their colors are black and their albedo is low. They are also called carbon-containing spherulites. It can be considered that this celestial body is the first material polymerized from the primitive nebula that gave birth to the solar system. They have not experienced any subsequent variation (such as melting caused by internal radioactive heating or structural transformation caused by meteorite impact).
Historical data and evidence of asteroid impact on the earth
1On the morning of June 30th, 908, a huge fireball more dazzling than the sun fell from the sky and landed with a bang. The shock wave knocked down trees in the surrounding virgin forest of more than 2,000 square kilometers, and the explosion spread to 1000 kilometers away. Experts estimate that its explosive power is equivalent to more than 20 million tons of hydrogen bombs, and it should weigh 40,000 tons when landing. This is the mystery of the famous Tunguska meteorite. Although some people think that this is a comet impact, there is no doubt that the earth is in danger of being hit, and people must not sit back and relax.
With regard to the extinction of dinosaurs 65 million years ago, there is now a widely accepted view that the perpetrator was an asteroid with a diameter of about 10 km. It hit the earth head-on, causing an unprecedented explosion, with energy equivalent to 65.438+0 trillion tons of high explosives. If it hits the land, mushroom clouds wrapped in countless rocks and dust will soar, just like thousands of hydrogen bombs explode, and the floating dust covering the sky will slowly spread and cover the whole world, and will gradually fall after several years. During this period, the sun will be blocked, the temperature will drop, the photosynthesis of plants will not be carried out, and the food source of dinosaurs will be cut off. If you fall into the ocean, its huge heat and kinetic energy will make hundreds of millions of tons of seawater suddenly evaporate and go straight into the sky, and at the same time set off an avalanche-like wave that swept across five continents in an instant. Whether it hits the land or the sea, it will trigger strong earthquakes, volcanic eruptions and tsunamis on a global scale at the same time. How did dinosaurs escape extinction?
According to the latest issue of Science, an international super-class academic journal published on February 23rd, 20001,several scientists from the University of Washington and the University of Rochester in new york recently discovered that a star similar to the above-mentioned asteroid hit the earth 250 million years ago, which caused the extinction of dinosaurs.
Not long ago, scientists from Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences made a rigorous scientific analysis of the abundant paleontological data in Changxing County, Zhejiang Province, and confirmed that the extinction of life on earth occurred 250 million years ago, not a gradual extinction or phased extinction as previously known, but a sudden catastrophic event.
Although the two events in the same period in geological history put forward by Chinese and American scientists are different in nature, they are by no means accidental coincidences, and the causal relationship is self-evident.
From the above three cases, it is proved that asteroids are the chief culprit of the impact on the earth. Some people may doubt it, but there are indeed traces of asteroid impact on the ground, which is beyond doubt. In the desert of Arizona, there is a Balinger crater with a diameter of1265m and an average depth of180m. It is estimated that this was formed by the impact of a meteorite with a diameter of 80 meters and a weight of 2 million tons, and such a large meteorite was an asteroid that traveled in space before landing.
As for the crater with a diameter of about 10 km, so far, three craters have been discovered, which are the traces left by the impact of asteroids on the earth since10.2 million years ago. Scientists have calculated that an asteroid with a diameter of 500 meters can hit such a big hole in the ground. This shows that it is possible for an asteroid with a diameter of 500 meters to hit the earth three times every million years. However, asteroids with smaller diameters are more likely to hit the earth, while asteroids with larger diameters are less likely to hit the earth.
In recent decades, astronomical observations have revealed many such threats from space. 1937 An asteroid named "Hermes" was discovered with a diameter of 1500m. According to calculation, its nearest distance to the earth may be only 300,000 kilometers, that is, it will pass between the moon and the earth, posing a terrible threat to the earth. Fortunately, the result was a near miss.
1968, Professor Batra of the University of Sydney warned that the asteroid Icarus was coming. "As long as it deviates slightly from the original orbit, it is possible to enter the route of collision with the earth." At that time, the asteroid approached the earth at a speed of 9 kilometers per second, with a diameter of 1000 meters and a mass of 2 billion tons. Only considering the mass, it should be 1000 times the energy of barringer meteorite. The disastrous consequences of its impact on the earth are unimaginable. This news caused an uproar in the media in Europe, America and Japan, and the believers and skeptics held their own words. On June 15 of that year, Icarus laughed at the argument between human beings in the space of 6.3 million kilometers from the earth and walked away. After all, the earth escaped.
1August, 972 10, a celestial body was observed flying in California, USA, with a distance of 580,000 kilometers. It is estimated to be an asteroid with a diameter of 10 kilometers.
On June198365438+1October1day, the American international infrared astronomical satellite discovered an asteroid with the temporary number 1983TB, and now its official name is "Phaeton". Astronomers calculate its orbit according to the information sent back by the satellite, which is once again frightening: when this asteroid comes again in 2 1 15, it may meet the earth.
199265438+On February 4th, an asteroid named Swift-tuttle, the size of a hill, swept through the earth's orbit at the speed of 0/00 times that of a shell/kloc. If its orbit is slightly deviated, the fate of the earth will be unimaginable.
At the beginning of 1997, the Beijing Observatory discovered a near-earth asteroid with a diameter of 1400 meters, and predicted that it was approaching the Earth. Later, it passed the earth with a distance of 75 thousand kilometers, which is only one-fifth of the distance between the earth and the moon. This earth adventure is really a close call, even scarier than the Hermes incident.
On March 8, 2002, an asteroid big enough to destroy a medium-sized city passed by the earth in a short distance of 463 thousand kilometers, but it was not discovered early. Four days later, astronomers discovered it on March 12. This asteroid is about 50 meters in diameter and comes from the direction of the sun. It is difficult for astronomers to find it.
Although the probability of an asteroid colliding with the earth is very small, the damage caused by the collision is often devastating.
If an asteroid with a diameter below 10 meter hits the earth, its energy is equivalent to 50,000 tons of TNT explosive, which will become a "meteorite fireball" in the atmosphere and burn itself into pieces. All this happened at high altitude and won't do much harm. This impact occurs about once every 10 years.
If an asteroid with a diameter of 10- 100 meters hits the earth, its energy is equivalent to tens of millions of tons of TNT, which will destroy a city and cause tens of millions of deaths. Once it falls in an earthquake-prone area, it will trigger an earthquake of magnitude 7.5 or above. This effect occurs about once every 300- 1000 years.
If an asteroid with a diameter greater than 100 meters hits the earth, its energy is equivalent to tens of millions of tons of TNT. If it falls in the middle of the ocean, it can trigger a tsunami as high as 200 meters on both sides. This impact occurs about once every 10000 years.
An asteroid with a diameter of more than 1.5km hits the earth, and if it falls into the ocean, it is enough to set off a huge wave with a height of 3000m m. Even 300 kilometers away, the waves will still be as high as 500 meters. If it attacks the land, there will be a "starry winter". At that time, the earth will be covered with thick dust and dark for several years. A quarter of the world's population will lose their lives and human civilization will go backwards. This kind of impact is estimated to occur every 500 thousand years.
Not long ago, the person in charge of the Near-Earth Object Monitoring Program announced that an asteroid with a diameter of 400 meters may collide with the Earth in 2029 with a probability of 1/300. The person in charge said: "In 2004, MN4 may collide with the Earth on Friday, April 13, 2029. We don't rule out this possibility now. If this unfortunate thing really happens, the consequences will be very serious. If you fall into the ocean, there will be a tsunami; If it falls on land, it will induce a severe earthquake and explosion. "
But we can rest assured that with the rapid development of science and technology, scientists will take various measures to prevent the possibility of collision. Experts from the National Aeronautics and Space Administration (NASA) who are in charge of the NEO monitoring program have officially announced that the possibility that the asteroid numbered 2004 MN4 will collide with the Earth in 2029 has been completely ruled out.
In addition, NASA scientists also confirmed that in the whole 2 1 century, the 2004 MN4 asteroid will not pose any threat to us.