2023-08-21 06:12:28
About half a billion celestial bodies orbit the sun and move through our solar system at speeds of regarding 30 km per second, potentially threatening the planet. Headlines appear on the Internet, almost every week, describing asteroids the size of a “bus”, “truck”, “vending machine”, “half the size of a giraffe” or, in fact, a whole giraffe. In addition to headlines warning of “killer” asteroids, “planet killer” and “God of Chaos”. And of course, the threats posed by asteroids are real. About 65 million years ago, life on Earth was affected by what was likely the impact of a large asteroid, killing most of the dinosaurs. What is the danger of a direct hit? Small asteroids cause much less damage than large asteroids. Therefore, the Earth experiences frequent but low-impact collisions with small asteroids, and rare but high-impact collisions with large asteroids. In most cases, the smallest asteroids pretty much disintegrate when they hit Earth’s atmosphere, not even reaching the surface. When a small asteroid (or meteor, an object smaller than an asteroid) hits Earth’s atmosphere, it produces a spectacular “fireball” – a long-period, bright version of a shooting star, or meteor. A very simplistic calculation gives an idea of how many asteroids you might expect to approach our planet. An asteroid measuring four meters across will cross Earth’s surface once a year, on average. Double the surface area, and you can expect two every year 6,400 kilometers from the Earth’s surface, and so on. Now, think of the really big asteroids, more than a kilometer in diameter. The same very simplified logic as above can be applied. It might be said that for every such impact that might threaten civilization, occurring once every half a million years or so, we can expect thousands of near misses (closer than the moon) in the same time period. Such an event will occur in 2029, when asteroid 153814 (2001 WN5) will pass at a distance of 248,700 km from Earth. How do we assess threats and what can we do regarding them? Almost 95% of asteroids larger than 1 km have been discovered, and the sky is constantly being searched for the remaining 5%. When a new asteroid is found, astronomers take extensive observations to assess any threat to Earth. The Torino Scale ranks projected threats up to 100 years in the future, and the scale ranges from 0 (no risk) to 10 (a specific collision with a large object). Currently, all known objects have a rating of zero. No known object has yet been rated higher than 4 (close encounter, warranting attention from astronomers). Finally, technology has advanced to the point where we have a chance to do something if we encounter a large number on the scale of Turin. Recently, the DART mission collided with an asteroid, causing it to change its trajectory. In the future, it is plausible that such a measure, with sufficient lead time, might help protect the Earth from collision. The report was prepared by Stephen Tingay, John Curtin Distinguished Professor (Radio Astronomy), Curtin University.
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