Tracking the threat of asteroids and comets

    Abdulaziz Sobh

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    In 1994, astronomers watched in amazement as Comet Shoemaker-Levy 9 crashed into the planet Jupiter, creating massive fireballs that exploded with the force of six million megatons of TNT, equivalent to 600 times the world's nuclear arsenal. What would have happened if I had hit Earth instead of Jupiter?
    "It would be the greatest destruction that humanity has ever seen," said Mel Stauffer, professor emeritus of geological sciences at the University of Saskatchewan. "It would not matter where it hit, it would affect all of humanity." The subject of Hollywood movies, the reality of asteroids and comet attacks is more science than science fiction. Most researchers believe that the probability of a massive object colliding with Earth in our life is small, but the planet has been hit before and will surely be attacked again. Stauffer has devoted his whole life to collecting evidence, searching for meteorites, breaking cones (violently fractured rocks around the edge of impact craters) and tektites (pulverized rock liquefied by the superheated temperature of an impact and released into the atmosphere before raining the surface ) Stauffer said on average that the Earth receives impacts by an asteroid of a meter of width approximately once a year, although the majority is burned in the atmosphere or it crashes in remote regions or in our vast oceans. Two of the most alarming recent events occurred in Russia's Siberian region, including the 2013 asteroid explosion near Chelyabinsk that was reported in the journal Nature as a house-sized object 20 meters in diameter, releasing the equivalent energy to 440,000 tons of TNT. "It passed a couple of villages, including Chelyabinsk, and because it broke the sound barrier and exploded into pieces, the shockwave broke the windows that exploded in the faces of the people, so that some 1,500 people were hospitalized by cuts, "said Stauffer. "It was the second largest event that we could measure accurately." In 1908, what is believed to be an asteroid exploded in a sparsely populated area of Siberia, crushing 80 million trees in more than 2,000 square kilometers of forest in what is known as the Tunguska event. More than 1,000 research papers have been presented on that explosion, with supercomputing simulations projecting the object as 60 to 190 meters wide and exploding with a force of up to 15 megatons of TNT (1,000 times more powerful than the dropped atomic bomb in Hiroshima in 1945). Chelyabinsk and Tunguska are the most recent examples of what can happen when an asteroid or comet collides with the planet. The Earth Impact Database documents 168 asteroid craters at least one kilometer in diameter, a list that includes the impact of 130km Sudbury - the third largest in the world - 1,800 million years ago, and the Chicxulub crater of 150km in the Yucatan Peninsula of Mexico created 65 million years ago that has been linked to the extinction of dinosaurs. The database includes six impact craters in Saskatchewan two kilometers or more: Viewfield, Gow Lake, Maple Creek, Codo, Deep Bay and Carswell (the largest with 39km wide), date from 75 million and 395 million years ago , as well as the 25km Crater of the Victoria Island in the Arctic that the professor of geological sciences of the U of S, Brian Pratt, helped discover in 2012 while exploring the area of Natural Resources Canada. "It was exciting," said Pratt, who co-authored an article on the finding in the research journal Meteoritics and Planetary Science. "We were flying in a helicopter and we could see that the rocks looked strange, so we landed and walked about 30 meters to the first outcropping of steep rocks and then we saw broken cones." We both looked at each other and said, "This is an impacting meteorite! That's what creates disintegrating cones, so we knew exactly what we were dealing with. " Pratt estimates that the impact occurred between 130 million and 450 million years ago and that it probably had far-reaching effects."It could have been a shallow sea when it hit, or it could have hit land, we just do not know for sure," he said. "If it were to land, there would be a lot of debris in the atmosphere that would have affected the climate, probably creating a cooling period."
    While the main asteroid attacks are rare in terms of Earth's 4.5 billion-year history, even another Tunguska-sized impact would have a devastating effect on a populated area. In the 1990s, Stauffer was a member of the National Advisory Committee on Meteorites and Impacts that requested the Canadian Space Agency and the National Aeronautics and Space Administration (NASA) in the United States to identify near-Earth objects (NEO). and track potential threats to the planet "They did not do anything immediately, but some amateur astronomers did and NASA finally paid attention and started their program, which I think I can claim a tiny little credit that our group got the bug in their ear." Stauffer said. To date, NASA has documented 18,043 NEOs in our solar system, including 1,900 that are at least 140 meters in diameter and have orbits close enough to Earth to be classified as potentially dangerous asteroids. But thousands remain undetected. On April 18, an asteroid labeled 2018GE3, estimated at up to 100 meters in diameter, escaped detection by NASA until a few days before moving halfway between Earth and the Moon (192,000km) at a speed of 106,000km per hour. "There are many asteroids and comets in our solar system and it is impossible to predict the trajectories of all these objects, but we have to try," said Daryl Janzen, professor of session physics at the University of S, who discusses NEOs in his Astronomy. 104 class. Identifying threats is the first step, with the United Nations recently supporting the establishment of the International Asteroid Alert Network for global collaboration to defend the Earth from potential impacts. While NASA's official position is that no known asteroid will collide with the planet this century, NASA is preparing for a 2021 space mission designed to demonstrate a kinetic impact technique to push an object out of a collision course with the Earth. "There is an extremely low probability that the planet will come into contact with one of these large near-Earth objects in our life, but there is really good evidence that it happened in the past and led to mass extinction on the planet," he said. Janzen. "So, although the probability is low, it is important to discover as many NEOs as we can, so that if one enters a collision course with the Earth, we can try to do something about it."