2021-11-29 06:11:28 GMT2021-11-29 14:11:28(Beijing Time) Sina English


Space rock alert: Should you worry about an asteroid impact?

NASA is testing one technique it might use should a large asteroid threaten to collide with Earth. But just how high are the odds of such a dangerous space rock after all? You don't need to panic.


The newly-launched Double Asteroid Redirection Test, or DART, is designed to test whether hitting an asteroid with a spacecraft can alter the rock's trajectory enough to avoid a predicted collision with the Earth, given enough lead time. The DART mission will target Dimorphos, which is a satellite of a larger asteroid called Didymos. There's no chance of the pair hitting Earth no matter how the NASA probe fares, according to mission personnel.

这个被称为“双小行星重定向测试任务”(DART)的航天器,旨在测试在足够的提前期的情况下,用航天器撞击小行星是否可以改变它的轨迹,以避免与地球发生可能的碰撞。 DART 任务将瞄准一颗名为Dimorphos的小行星,它是一颗名为 Didymos 的更大小行星的卫星。据工作人员介绍,无论美国宇航局的探测器的撞击结果如何,这对小行星都不会对地球构成威胁。

So Didymos and Dimorphos don't pose a threat — but are asteroid impacts something most people need to worry about? The answer, as with many things, is "it's complicated."

所以 Didymos 和 Dimorphos 不会构成威胁——但小行星撞地球是我们普通人需要担心的吗?与许多事情一样,答案是“这很复杂”。

Countless tiny impacts


First off, the question isn't whether an asteroid will smash into the Earth: Not only has it happened before, but it happens pretty routinely.


Small rocks impact all the time — something the size of a small car hits Earth's atmosphere about once a year, according to NASA, but objects of that size burn up in the atmosphere and explode well before they hit the ground.


When this occurs, no one really notices, since these rocks cause what we call meteors — the "shooting stars" we enjoy watching on a dark, clear night. Meteors are produced by meteoroids, which are the actual pieces of asteroid that are burning up. The vast majority of meteoroids are fractions of an inch or a few millimeters across.


Once in a while, meteoroids are large enough to get deep in the Earth's atmosphere and explode; these objects are called bolides or fireballs. Occasionally a bolide will survive until close enough to Earth's surface that bystanders hear the explosion; some airblasts can damage local homes like a bomb, as happened at the Russian town of Chelyabinsk in 2013.

偶尔,流星体大到足以深入地球大气层并爆炸;这些物体被称为火流星或火球。有时,一个火流星体会足够接近地球表面以至于旁观者可以听到爆炸声;有些爆炸可以像炸弹一样损坏房屋,如2013 年在俄罗斯车里雅宾斯克市的流星坠落事件。

In general, there are a lot more small objects orbiting the sun than large ones, and the progression is roughly logarithmic — for every million sand-grain-size objects, there will be only one that weighs 2 pounds (1 kilogram), and generally there are a trillion tiny meteors for each object in the range of 2,000 pounds (1,000 kg).


A small risk of a big impact


Scientists take a variety of approaches to try to understand the relative risk of a serious asteroid impact on Earth.


Consider the most recent larger impacts. In 1908, a large asteroid or comet exploded over Siberia, triggering shock waves that flattened some 750 square miles of forest in what is dubbed the Tunguska event. The next notable impact, over Chelyabinsk, occurred about 100 years later and damaged homes as far as 55 miles (88 kilometers) away on either side of its trajectory. The Chelyabinsk impact caused some 1,200 injuries.

最近的几次产生较大影响的撞击事件有: 1908 年,一颗较大的小行星或彗星在西伯利亚上空爆炸,引发了冲击波,将大约 750 平方英里的森林夷为平地,此次流星撞击事件被称为通古斯事件。另一次较大的撞击发生在大约 100 年后,发生地在俄罗斯车里雅宾斯克,损坏了小行星坠落轨迹55 英里(88 公里)范围内的房屋,并且造成1200人受伤。

Statistics gathered by Clark Chapman at the Southwest Research Institute compare a typical American's risk of dying from various causes. Dying from a global impact, which could be smaller than that of the famous Chicxulub asteroid that ended the reign of the dinosaurs about 66 million years ago? About 1 in 75,000. The chances of dying from a regional impact that doesn't affect the entire Earth are actually smaller, about 1 in 600,000.

西南研究所的克拉克查普曼(Clark Chapman)收集的统计数据表明:一名普通的美国人死于小行星撞击地球的风险大约是75000分之一,可能比大约 6600 万年前结束恐龙统治的著名的希克苏鲁伯小行星的撞击可能性还小?死于不影响整个地球的区域性撞击的几率实际上更小,约为 600,000 分之一。

These are not large odds, but they are actually better than the chances of winning your local Powerball lottery on a specific ticket.


However, the chances of being killed in an asteroid impact shouldn't keep you up at night. Chapman, who gathered these numbers in 2007, found that an average American had 1 in 30,000 odds of dying in a plane crash and 1 in 60,000 odds of dying in a tornado; either of those fates is much more likely to be the cause of your demise than an asteroid impact.

然而,在小行星撞击中丧生的机率不应该让你夜不能寐。根据查普曼在 2007 年收集的数据,普通美国人死于飞机失事的几率为 30,000 分之一,死于龙卷风的几率为 60,000 分之一;与小行星撞击相比,这两种厄运中的任何一种都更有可能导致您的死亡。

Or consider COVID-19. Some 770,000 Americans have died of COVID-19 since the start of the pandemic, according to the Centers for Disease Control and Prevention. The population of the United States is roughly 329 million people, so over the past two years approximately 1 in 427 people have died from the virus. Clearly, COVID-19 is much more likely to kill you than an asteroid impact.

或者看看新冠疫情。根据美国疾病控制与预防中心的数据,自新冠疫情开始以来,约有 770,000 名美国人死于新冠病毒。美国人口约为 3.29 亿,因此在过去两年中,大约每 427 人中就有 1 人死于该病毒。显然,与小行星撞击相比,新冠病毒更有可能杀死您。

The bottom line: you need not worry too much about an asteroid impact compared to many other risks, but it is a longer-term problem that humanity must deal with.


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