Collision between the Earth or other planets and asteroids, comets and other celestial bodies
Impact event refers toearthOr other planets collide with asteroids, comets and other celestial bodies.According to historical records, hundreds of small impact events (including fireball explosions) that caused casualties and property losses in specific areas were recorded.Impact events at sea may cause tsunami damage to the sea and coast.
The incident of Comet Sumek Levy 9 hitting Jupiter in 1994 was an "alarm bell" to mankind, so astronomers began to carry out many sky finding plans and began to search for asteroids, such as Lincoln Near Earth Asteroid Research Group, Near Earth Asteroid Tracking, Lowell Observatory Near Earth Asteroid Search Plan and other plans, which greatly increased the discovery rate of asteroids.
In 1998, two comets were observed approaching the sun at a relatively close distance. The first comet was found on June 1 of that year, and the second comet was found the next day.NASAA video on the website shows that after the two comets approached the sun, the sun dramatically ejected a large amount of material (possibly unrelated to the impact).These two comets should have evaporated before hitting the sun's surface.according toJet Propulsion LaboratoryAccording to the research of the scientist Zden ě k Sekanina, the latest event that really hit the sun's surface was a "super comet" Comet Howard Koomen Michels hitting the sun on August 30, 1979.
On October 7, 2008, an asteroid named 2008TC3 was tracked for 20 hours when it approached the Earth, and exploded over Sudan when it entered the Earth's atmosphere.This is the first time that an object has been detected before entering the earth's atmosphere, and its hundreds of meteorite fragments are scattered in the Nubian Desert.
On July 19, 2009, an amateur astronomer found a newly formed Earth sized black spot in the southern hemisphere of Jupiter.Thermal infrared analysis found that the temperature of this area was higher than that of the surrounding area, and ammonia was found in the spectrum.Scientists at the Jet Propulsion Laboratory determined that another impact event occurred in 2009, which may be caused by the impact of small comets or other ice bodies that have not yet been discovered.
The third generation wide area camera of the Hubble Space Telescope photographed the slow change process of debris from asteroid P/2010A2.The asteroid may collide with a smaller asteroid.
From May to June 2010,hubble space telescope The third generation wide area camera of the Landsat has taken an image of the irregular X-shaped debris after the impact of asteroid P/2010A2 and another smaller asteroid.
Mass extinction
Announce
edit
In the past 540 million years, there have been five large-scale extinction events that have been widely accepted, and each time on average, at least half of the species on Earth have been extinct.The largest extinction event was the Permian Triassic extinction event at the end of the Permian Period 250 million years ago, which caused 90% of the creatures on the earth to become extinct;After the extinction event, the number of living things on the earth recovered to the diversity before the extinction event 30 million years ago.The age of the impact crater that may have caused the extinction event is still controversial. The impact crater is the Bedeo Plateau, but whether the impact crater is related to the extinction event is still controversial.The last mass extinction event was the Cretaceous Tertiary extinction event when a giant meteorite hit the earth 65 million years ago, causing the extinction of dinosaurs.So far, there is no other conclusive evidence to prove that the other four extinction events are related to the impact events.It was found that in 1980, physicist Luis Walter Alvarez and his son Walter Alvarez, a geologist, as well as two nuclear chemists Frank Asaro and Helen Michel from the University of California, Berkeley, found that there was unusually high concentration of iridium in a specific stratum of the crust.Iridium is a rare element on the earth's surface, but it has relatively high content in meteorites.According to the distribution and content of the 65 million year old "Iridium layer" in the world, the Alvarez team estimated that an asteroid with a diameter of 10 to 14 kilometers hit the Earth.Iridium bearing strata at the K-T boundary have been found in more than 100 places around the world.The polyhedral shock quartz (coesite) is formed only at the site of nuclear weapon explosion or large impact events, and the mineral is also found in more than 30 locations around the world.The soot and burning ash found in these strata are tens of thousands of times of the general value.
find
The anomalous chromium isotope ratio in the K-T boundary strata is also strong evidence of the impact theory.The chromium isotope ratio is fairly average on the earth, so the abnormal chromium isotope ratio and the abnormal high iridium content can be ruled out to be caused by volcanism.In addition, the chromium isotope ratios measured at the K-T boundary are quite similar to those measured in carbonaceous chondrites.Therefore, the possible impact event is carbon asteroid or comet, and the composition of comet is quite similar to carbon chondrite.
Perhaps the most credible evidence of this global disaster event is the discovery of the largeMeteorite crater。The impact crater is located in the Yucatan Peninsula, Mexico, and was discovered by Glen Penfield and Tony Camargo, two geophysicists working for the Mexican oil company.Their report pointed out that the annular structure may be an impact crater with a diameter of about 180 km.Other researchers found that the Cretaceous Tertiary extinction event wiped out dinosaurs in only a few thousand years, rather than millions of years previously thought.Therefore, most scientists believe that the extinction event is more likely to be an impact event image from outside the earth, rather than a volcano or climate change that takes longer to affect.
Since the 20th century, several craters have been found around the world that are roughly the same as the Hiksurub crater for several years.For example, Silver Crater Crater in Britain, Potes Crater in Ukraine, and Siva Crater near India.This led scientists to believe that Hick Sulub Crater was one of several impact events that occurred almost at the same time, quite similar to the event that comet Sumek Levy 9 crashed into Jupiter after splitting in 1994.
development
Up to 2012, there is still a lack of iridium anomaly and shock quartz evidence to support the relationship between the Permian Triassic extinction event and the impact event, although some impact craters that may be related to the extinction event have been found, such as the Wilkes Crater and Bedeo Plateau.In the late Permian, all the landmasses gathered into a supercontinent Pangea, and the rest of the earth's surface was a pan ocean.If the impact event occurs in the sea, not on land;It will form less shock quartz (because the ocean crust contains relatively less silica) and other materials.
Although it is generally believed that a huge impact event ended the Cretaceous and produced iridium rich strata on the K-T boundary, other impact residues of similar scale show that no extinction event has occurred, and there is no connection between the impact event and other factors that caused the extinction event.Nevertheless, it is generally believed that extinction events caused by impact events are random events in the history of the Earth.
Paleontologists David M. Raup and Jack Sepkoski proposed that there would be an extinction event every 26 million years, although many of them were on a smaller scale.This led the physicist Richard A. Muller to propose the hypothesis that the extinction event might be an imaginary solar companion, Nemesis, which would periodically disturb the comets in the Oort Cloud, and make a large number of comets enter the inner solar system, increasing the possibility of the Earth being hit by comets.
Indeed, in the early history of the Earth (about 4 billion years ago), the Earth was frequently impacted because there were a large number of protostars and other materials in the early solar system.These impact events may be caused by asteroids hundreds of kilometers in diameter, and the energy generated is enough to evaporate all the Earth's oceans.Life on the earth will not evolve until the number and scale of impacts are greatly reduced.If such an impact happens in modern times, it will destroy human civilization.Fortunately, there are fewer large objects in the solar system than before, and the probability of such an impact is almost zero;This is because the large asteroids or comets in the Asteroid Belt and the Cooper Belt are in stable orbits, have not entered the inner solar system, and are unlikely to intersect the Earth orbit, without any exception.
The most widely believed theory of the formation of the moon is the big collision theory, which means that the earth may have collided with a Mars sized micro planet in the early days.If this theory holds, it will be the strongest impact the earth has ever suffered.The special rotation and tilt angle of rotation axis of some planets may also be related to this. For example, Venus's retrograde rotation and Uranus's great tilt angle of rotation axis are both considered to be possibly impacted by a huge impact, which also conforms to the theory of solar system and planet formation.However, there is still no relevant evidence in Venus and Uranus to prove that the giant impact event changes the rotation mode of the planet.
The end of human civilization
Announce
edit
The impact event is often considered as the scene that caused the end of human civilization.In 2000, Discovery magazine listed 20 possible events that would lead to the end of human civilization, and the impact event was listed as the first, that is, the most likely event.Until the 1980s, this topic was ignored for a long time, until the discovery of Hick Sulub crater, and after Comet Sumek Levy 9 hit Jupiter, the public paid more attention to this topic.
