VOA慢速英语2021 科学家提出造成恐龙灭绝的新理论（在线收听）

American researchers have a new theory about how an object struck the Earth and caused the dinosaurs to die off.

美国研究人员对某个物体如何撞击地球并导致恐龙灭绝有了新的理论。

Scientists mostly agree on where the impact happened about 65 million years ago. They say a huge object struck an area off the coast of what is now Mexico. Astronomers have said the most likely cause of the strike was either an asteroid or a comet.

科学家们对大约6500万年前这次撞击发生的地点取得了一致意见。他们表示，一个巨大物体击中了现在墨西哥沿海的一片区域。天文学家表示，造成这次撞击的最可能原因是小行星或彗星。

In recent years, researchers have presented evidence that the impact was caused by an asteroid. The theory suggests the asteroid came from an area between the orbits of Mars and Jupiter.

近年来，研究人员提出了证据证明这次撞击是小行星造成的。这种理论表明，这颗小行星来自于火星与木星轨道之间的区域。

But a study by two astronomers from Harvard University presents a new theory: that the crash was caused by a comet. The researchers say the comet came from an area containing icy debris on the edge of the solar system. The area is known as the Oort cloud.

但是，哈佛大学两位天文学家进行的一项研究提出了一种新理论，那次撞击是由彗星引起的。研究人员表示，这颗彗星来自于太阳系边缘一处含有冰雪碎块的区域。该区域被称为奥尔特云。

Their theory states that the comet was pulled into the solar system by Jupiter's gravity. The comet then came very close to the sun, whose tidal force caused it to break up into pieces. The researchers believe one of the pieces crashed into the place that scientists have identified in Mexico.

他们的理论指出，这颗彗星是被木星的引力拽入太阳系的。然后这颗彗星靠近太阳，在潮汐力作用下裂成碎片。研究人员认为，其中一块碎片坠入了科学家在墨西哥确定的地点。

The team based its theory on a model created to predict the probability that a long-period comet from the Oort cloud would hit Earth. Long-period comets take more than 200 years to orbit the Sun.

该小组的理论是基于一个旨在预测奥尔特云长周期彗星撞击地球可能性的模型。长周期彗星绕太阳公转需要200多年时间。

Because comets come from frozen areas of the outer solar system, they are icier than asteroids. They are known for leaving long trails of gas and dust as they melt.

因为彗星来自于外太阳系的冰冻区域，所以它们比小行星更冰冷。它们因融化时留下大量气体和灰尘而闻名。

The new study was recently published in Scientific Reports. The lead author was Amir Siraj, an astrophysics student at Harvard. "Jupiter is so important because it's the most massive planet in our solar system," he told the French press agency AFP.

这项新研究最近发表在《科学报告》上。主要作者是哈佛大学天体物理学系学生阿米尔·西拉杰。他对法新社表示：“木星非常重要，因为它是我们太阳系中最大的行星。”

Siraj said the findings showed that Jupiter's large influence pushes "these incoming long-period comets into orbits that bring them very close to the sun." The comets experience such a large tidal force from the sun "that the most massive of them would shatter into about a thousand fragments," he said. Each of those fragments would be large enough to produce a crater the size of the Mexican site, he added.

西拉杰表示，研究结果表明，木星的巨大引力将这些刚进入的长周期彗星推到使他们非常接近太阳的轨道。他说，这些彗星承受着来自太阳的巨大潮汐力，其中质量最大的会破碎成大约一千块碎片。他还表示，这些碎片中的每一块都足够大，足以形成一个墨西哥撞击点大小的陨石坑。

That massive impact is estimated to have been equal to the strength of about 10 billion nuclear bombs. The U.S. Space Agency NASA has estimated the strike created a huge crater about 180 kilometers wide and 900 meters deep.

据估计那次巨大的撞击相当于大约100亿枚核弹的力量。美国宇航局估计，这次撞击造成了一个宽约180公里，深度约900米的巨大陨石坑。

The event is believed to have caused widespread wildfires, earthquakes and ocean waves. It also released chemicals into the atmosphere, leading to severe cooling. Scientists blame the event for destroying more than 70 percent of plant and animal life. In addition, all dinosaurs that were not bird-like died out.

据信这次撞击事件引发了大范围野火、地震和海浪。它还将化学物质释放到大气中，导致严重的降温。科学家们认为该事件毁灭了70%的动植物生命。此外，所有非类鸟恐龙都灭绝了。

The researchers say their theory can be tested by further studying the crater in Mexico, as well as possibly those on the moon. In addition, space explorers might also be sent to collect comet material for examination.

研究人员表示，他们的理论可以通过进一步研究墨西哥和以及月球上可能的陨石坑来进行检验。此为，还可能派出太空车来收集彗星材质来进行检验。

The study also suggests that similar impacts can be expected to strike Earth about once every 250 to 730 million years. But the other lead researcher on the project, Harvard professor Avi Loeb, noted that that is just an estimate.

研究还表明，预计大约每250年到7.3亿年地球会经历一次类似撞击。但是该项目的另一位主要研究员、哈佛大学教授阿维·洛布指出，这只是一种估算。

"You never know when the next one will come," he said. "The best way to find out is to search the sky."

他说：“你永远不知道下一次撞击何时到来。找出答案的最好办法就是搜寻天空。”