Level 4 Reading 12B

Reading 12B

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THE THREAT FROM SPACE It was just after 9 p.m. on June 18, 2004, at an observatory in Arizona, in the United States. Astronomer David Tholen was scanning the sky for asteroids when he noticed an object headed toward Earth. He and his colleagues hoped to take a closer look later that week but, unfortunately, were prevented by rain. By the time the team finally got another look at it, they realized they had a problem. The object was a large asteroid, which they named Apophis, after the Egyptian god of evil. Bigger than a sports arena, it comes frighteningly close to our planet every few years. By December, Tholen had calculated that the chance that Apophis would smash into Earth on April 13, 2029, was one in 40. Alarm about the threat started to spread. Then, on December 26, 2004, a real catastrophe struck: the Indian Ocean tsunami, which claimed hundreds of thousands of lives. The public forgot about Apophis. Meanwhile, astronomers had found earlier images of the asteroid. The extra data enabled them to calculate its orbit, and they discovered that it would actually fly safely by Earth in 2029. However, this alarming scenario started a race among scientists to find solutions to the threat of large objects striking Earth. Near Misses Every day, tons of dust from comets and pieces of asteroids the size of grains of sand burn up in the Earth's upper atmosphere. Most days, a piece or two of rock or metal—the size of an apple or bigger—actually makes contact with Earth. Yet it's unlikely you'll ever be struck by a meteorite. Very few meteorites are ever known to have hit a person. In 1954, a grapefruit-sized rock bounced off Ann Hodges's radio and hit her as she lay on her sofa near Sylacauga, Alabama, in the United States. She escaped with only a bruised hip and wrist. Since then, there have been some spectacular near misses. On August 10, 1972, an object the length of a car and weighing 150 tons traveled through the upper atmosphere. Hundreds of people saw its bright trail that sunny afternoon as it crossed the sky from Utah, in the United States, to Alberta, Canada, before flying back out into space. On March 22, 1989, a rock measuring 300 meters across came within several hundred thousand kilometers of Earth, which—in astronomical terms—is uncomfortably close.

来自太空的威胁 2004年6月18日晚9点刚过，在美国亚利桑那州的一个天文台。 天文学家大卫·托伦在天空中扫描小行星时，发现了一个朝向地球的物体。 他和他的同事们希望在本周晚些时候进行更仔细的研究，但不幸的是，由于下雨而无法进行。 当团队最终再次审视它时，他们意识到自己遇到了问题。 该物体是一颗大型小行星，他们以埃及邪恶之神阿波菲斯的名字将其命名。 它比体育场还大，每隔几年就会惊人地靠近我们的星球。 到12月，托伦已经计算出，阿波菲斯在2029年4月13日撞击地球的几率是40%。 关于威胁的警报开始蔓延。 然后，在2004年12月26日，一场真正的灾难发生了： 印度洋海啸夺去了数十万人的生命。 公众忘记了阿波菲斯。 与此同时，天文学家已经发现了这颗小行星的早期图像。 额外的数据使他们能够计算出它的轨道， 他们发现，它实际上会在2029年安全地飞过地球。 然而，这一令人担忧的情况引发了科学家们为解决大型物体撞击地球的威胁而展开的竞赛。 未遂事件 每天，来自彗星和沙粒大小的小行星碎片的大量尘埃在地球高层大气中燃烧。 大多数时候，一两块苹果大小或更大的岩石或金属实际上会与地球接触。 然而，你不太可能被陨石击中。 已知很少有陨石撞击过人。 1954年，一块葡萄柚大小的石头从安·霍奇斯的收音机里弹了出来 在美国阿拉巴马州锡拉库加附近，当她躺在沙发上时，她遭到了殴打。 她逃脱时，臀部和手腕都擦伤了。 从那以后，发生了一些壮观的未遂事件。 1972年8月10日，一个长如汽车、重150吨的物体穿过高层大气。 在那个阳光明媚的下午，当它从美国犹他州横跨天空到达加拿大阿尔伯塔省时，数百人看到了它明亮的踪迹， 在飞回太空之前。 1989年3月22日，一块直径300米的岩石在距离地球几十万公里的范围内出现， 从天文学的角度来看，这非常接近。

Smash Hits There is evidence that, in the past, massive comets or asteroids have struck Earth's surface. Thirty-five million years ago, a 3-kilometer-wide rock smashed into the ocean floor, 160 kilometers from what is now Washington, D.C., leaving an 85-kilometer-wide crater buried beneath Chesapeake Bay. Another giant rock called Titan—10 kilometers in diameter—smashed into the Gulf of Mexico around 66 million years ago, unleashing thousands of times more energy than all the nuclear weapons on the planet combined. "The whole Earth burned that day," says Ed Lu, a physicist and former astronaut. Three-quarters of all life forms, including the dinosaurs, went extinct. Astronomers have identified numerous asteroids big enough to cause a catastrophe for the entire planet. None is on course to do so in our lifetimes, but there are many smaller asteroids that could strike—with devastating effects—in the near future. On June 30, 1908, an object as big as a 15-story building fell in Tunguska, a remote part of Siberia. The object—an asteroid or a small comet—exploded several kilometers before impact, burning and blowing down trees across 2,000 square kilometers. Clouds of tiny particles of dust and ice filled the sky. The particles reflected the sun's light onto the Earth, and for days people in Europe could read newspapers outdoors at night. More recently, in 2013, a 20-meter meteor exploded over Chelyabinsk Oblast, Russia, injuring dozens of people on the ground. It was the largest object to enter the Earth's atmosphere since Tunguska. The next time a large object falls out of the sky, we may be taken by surprise— though an early-warning system for near-Earth objects has recently been put into place. Sky surveys—like the one done by Tholen—are also helping to fill the gap. "Every couple of weeks," says Lu, "we're going to be finding another asteroid with, like, a one-in-a-thousand chance of hitting the Earth." What Can Be Done? Within decades, the world's leaders may be faced with a dilemma: what to do about an incoming space object. Few experts are giving this much thought, according to NASA astronomer David Morrison. "The number would roughly staff a couple of shifts at McDonald's," he says. Ed Lu—one of these few experts—is working on a plan that employs a spaceship to deflect asteroids. "We were originally thinking about how you would land on an asteroid and push it," he says. "But that doesn't work well." If the surface isn't solid, you have trouble landing or keeping anything on it. Moreover, asteroids are always rotating. Pulling the asteroid along would be much easier. "Rather than having a physical line between you and the thing you're towing, you're just using the force of gravity between them,"Lu says. A nearby spacecraft would pull the asteroid off course very slowly but steadily, using only gravity. Just a slight change in course could mean missing Earth by tens of thousands of kilometers. An Asteroid Bomb? The drawback to Lu's plan is that it would work only for asteroids up to a few hundred meters across that could be engaged far from Earth. Russian scientist Vadim Simonenko and his colleagues concluded that the best way to deflect a larger asteroid up to 1.5 kilometers wide would be to explode a nuclear bomb nearby. The explosion would destroy smaller rocks. For larger ones, the explosion would burn a layer of rock off the asteroid's surface. The expanding gas would act as a rocket motor, pushing the asteroid onto a new course. As Apophis swings past Earth in 2029, there is a small chance that Earth's gravity will deflect the asteroid just enough to put it on a certain collision course with our planet on the next pass, in 2036. The odds are currently estimated at one in 45,000, so a strike is extremely unlikely. Meanwhile, astronomers will continue to track Apophis to learn if it will merely tauntus again, or actually strike.

非常流行 有证据表明，在过去，巨大的彗星或小行星撞击过地球表面。 3500万年前，一块3公里宽的岩石撞击了海底， 距离现在的华盛顿特区160公里，切萨皮克湾下埋有一个85公里宽的陨石坑。 另一块名为泰坦的巨石，直径10公里，大约6600万年前坠入墨西哥湾， 释放的能量是地球上所有核武器总和的数千倍。 物理学家、前宇航员Ed Lu说：“那天整个地球都被烧毁了。”。 四分之三的生命形式，包括恐龙，都灭绝了。 天文学家已经发现了许多大到足以给整个星球带来灾难的小行星。 在我们有生之年，没有一颗小行星会这样做，但在不久的将来，有许多较小的小行星可能会撞击地球，造成毁灭性的影响。 1908年6月30日，一座15层楼高的物体在西伯利亚偏远的通古斯卡坠落。 该物体——一颗小行星或一颗小彗星——在撞击前几公里爆炸， 烧毁和吹倒2000平方公里的树木。 天空中布满了微小的尘埃和冰块。 这些粒子将太阳光反射到地球上，欧洲人可以在夜间户外阅读报纸好几天。 最近，在2013年，一颗20米长的流星在俄罗斯车里雅宾斯克州上空爆炸，造成地面数十人受伤。 它是自通古斯以来进入地球大气层的最大物体。 下一次当一个大物体从天而降时，我们可能会大吃一惊-- 尽管最近已经建立了近地天体预警系统。 像Tholen所做的天空调查也有助于填补这一空白。 “每隔几周，”陆说， “我们将发现另一颗小行星，撞击地球的几率大约是千分之一。” 我们能做什么？ 几十年内，世界各国领导人可能会面临一个困境：如何应对即将到来的太空物体。 美国国家航空航天局天文学家大卫·莫里森表示，很少有专家对此进行过多思考。 他说：“这个数字大致相当于麦当劳的几个班次。”。 陆是为数不多的专家之一，他正在研究一项利用宇宙飞船偏转小行星的计划。 他说：“我们最初考虑的是如何降落在小行星上并推动它。”。 “但这行不通。”如果表面不坚固，你就很难在上面着陆或保持任何东西。 此外，小行星总是在旋转。 拉动小行星会容易得多。 陆说：“与其在你和你拖动的东西之间有一条物理线，不如在它们之间利用重力。”。 附近的航天器将仅利用重力缓慢但稳定地将小行星拉离轨道。 航向的微小变化可能意味着地球将消失数万公里。 小行星炸弹？ 陆的计划的缺点是，它只适用于直径达几百米、可以远离地球的小行星。 俄罗斯科学家瓦迪姆·西蒙年科和他的同事 得出的结论是，偏转1.5公里宽的较大小行星的最佳方法 这将是在附近引爆核弹。 爆炸会摧毁较小的岩石。 对于较大的小行星，爆炸会烧毁小行星表面的一层岩石。 膨胀的气体将充当火箭发动机，将小行星推向新的轨道。 当阿波菲斯在2029年掠过地球时，地球引力使小行星偏转的可能性很小 在2036年的下一次穿越中，它将与我们的星球发生某种碰撞。 目前估计，这种可能性为45000分之一，因此罢工的可能性极小。 与此同时，天文学家将继续追踪阿波菲斯，以了解它是否会再次嘲讽我们，或者是否真的会撞击我们。

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