These small objects usually burn up high in the atmosphere, producing the shooting stars you may have seen while looking up at the night sky.

這些小物體通常會在大氣層中燒起，變成你仰望夜空時，可能會看見的流星。

But astronomers are always on the lookout for bigger asteroids, especially the ones that may be on course to strike our planet.

但天文學家總在密切關注更大型的小行星，尤其是那些很可能撞擊我們星球的。

While rare, these collisions with rocks from deep space do happen and the results can be downright terrifying.

儘管稀少，這些來自外太空的石頭碰撞地球確實有可能發生，且後果極為駭人。

An asteroid just seven meters in diameter will explode with the power roughly equal to the atomic bomb that was used on Hiroshima, leveling buildings up to a mile away.

一顆直徑 7 公尺的小行星爆炸的威力大約與使用在廣島的原子彈一樣，能把建築物升起至一英里高。

A larger one hundred meter diameter asteroid has more power than the largest nuclear weapon ever tested and could level an entire city!

一個更巨大，直徑 100 公尺的小行星具有比有史以來測試過的最大核武更強的破壞力，可以將一座城市夷為平地！

But there are even bigger asteroids out in space.

但宇宙中甚至有比這更大的小行星存在。

And a run in with one of these would have a truly global impact.

這之中若有一顆碰撞地球，一定會造成全球性影響。

An insanely giant asteroid, one around ten kilometers in diameter, would create an impact crater one hundred and eighty kilometers wide and twenty kilometers deep.

一顆直徑大約 10 公里的超大型小行星碰撞會造成 180 公里廣、20 公里深的撞擊坑。

Beyond just the impact it would cause worldwide earthquakes and mega tsunamis over one hundred meters high.

除了這個影響外，也會造成全球地震和超過 100 公尺高的巨型海嘯。

Dust and ash thrown up into the atmosphere would cover the surface of the earth for years.

塵土和灰燼被排放到大氣層中，覆蓋地球表面數年。

A massive die off of plants and animals would follow.

隨後，大量動植物會全部死亡。

Basically the end-of-life as we know it.

基本上就是我們所知的生命盡頭。

And this has happened before.

而這之前確實發生過。

An asteroid of roughly that size is what we think killed the dinosaurs.

我們認為滅絕恐龍的就是大約這個大小的小行星。

And if an enormous asteroid the size of the earth were to hit, the planet would be completely obliterated, leaving nothing but the earth's core and creating a new asteroid belt between Venus and Mars.

若有個跟地球相同體積的小行星撞擊地球，地球將徹底消失僅留下地核，創造金星與火星之間新的小行星帶。

But don't worry too much.

但不用太擔心。

Giant asteroids the size of the one that wiped out the dinosaurs only hit the earth about every fifty to one hundred million years.

將恐龍滅絕的那種巨型小行星每 5000 萬到 1 億年才會撞擊地球一次。

Of course, the last one was sixty-six million years ago so I guess you could say we are due.

想當然耳，距離上一次是 6600 萬年前，所以我猜你可以說我們是安全的。