Dangers from outer space

[00:00.40] What is the greatest threat to life on our planet? Is it climate change? 我们星球上生命面临的最大威胁是什么？是气候变化吗？

[00:05.18] Shortages of food or water? Or might an altogether bigger danger come from somewhere further away: space?食物或水短缺？或者一个更大的危险可能来自更远的地方：太空？

[00:12.09] We’re not talking about an invasion by little green men here.我们不是在谈论小绿人的入侵。

[00:17.40] Instead, how about the prospect of being hit by a gigantic meteorite, zapped by lethal cosmic rays or fried by the deadly energy of an erupting star?相反，被巨大的陨石击中、被致命的宇宙射线击中或被喷发的恒星的致命能量炸毁的前景如何？

[00:29.62] It wouldn’t be the first time. Good old planet Earth has had a rough ride over the last 3.7 billion years, with some spectacularly devastating events. 这不会是第一次。在过去的 37 亿年里，古老的地球经历了一段艰难的旅程，发生了一些惊人的毁灭性事件。

[00:40.24] The most famous mass extinction was 66 million years ago, when it’s widely believed a meteorite killed off the dinosaurs.最著名的大灭绝发生在 6600 万年前，当时人们普遍认为是陨石杀死了恐龙。

[00:49.27] A 110-mile-wide crater in Mexico with the same geological age supports this theory.墨西哥一个 110 英里宽、地质年代相同的陨石坑支持了这一理论。

[00:57.51] Believe it or not, this wasn’t the most brutal episode in our planet’s history. 信不信由你，这不是我们星球历史上最残酷的事件。

[01:03.09] That was when a staggering 96% of life was wiped out at the end of the Permian period, 252 million years ago. 那是在 2.52 亿年前的二叠纪末期，惊人的 96% 的生命被消灭。

[01:12.65] Scientists don’t know for sure why this happened, but any potential explanations carry with them the grim possiblity that similar events could happen again.科学家们不确定为什么会发生这种情况，但任何潜在的解释都带有类似事件可能再次发生的严峻可能性。

[01:23.01] For example, some experts believe that our Sun has a very dense, dim twin star which is too far away to observe directly.例如，一些专家认为我们的太阳有一颗非常密集、昏暗的双星，距离太远而无法直接观察。

[01:32.31] This sleeping giant, dubbed the “Death Star”, could distort the paths of orbiting chunks of icy rock and hurl them towards the rest of the Solar System.这个沉睡的巨人，被称为“死星”，可以扭曲冰块的轨道并将它们抛向太阳系的其他部分。

[01:42.67] Is this what happened 252 million years ago? Or is there instead, perhaps, a distant, ninth planet in our Solar System which pulls in passing comets and sends them hurtling our way?这是2.52亿年前发生的事情吗？或者，我们太阳系中是否有一颗遥远的第九颗行星，它会吸引路过的彗星并让它们飞向我们的方向？

[01:57.27] If that isn’t enough to put you off your breakfast, then consider what’s happening to our friend, the Sun. 如果这还不足以让您不吃早餐，那么请考虑一下我们的朋友太阳发生了什么事。

[02:12.95] The star that has given us the warmth to sustain life is gradually turning into a deadly foe.给我们温暖以维持生命的那颗星星正在逐渐变成一个致命的敌人。

[02:14.27] Like all stars, it is slowing dying, burning through its energy supplies. 像所有恒星一样，它正在减慢死亡速度，消耗其能量供应。

[02:17.99] As it does so, it expands, and in about 2 billion years it will have grown so much that the heat will make life on planet Earth unbearable.当它这样做时，它会膨胀，在大约 20 亿年的时间里，它会增长得如此之快，以至于热量将使地球上的生命难以忍受。

[02:26.49] While all this sounds a little macabre, take comfort from the fact that the chance of being hit by a giant interstellar projectile is incredibly slim, and that 2 billion years is a very long time.虽然这一切听起来有点令人毛骨悚然，但请放心，被巨大的星际弹丸击中的机会非常渺茫，而且 20 亿年是一段很长的时间。

[02:39.24] And there’s another thing: if the dinosaurs had not snuffed it when they did, it’s extremely unlikely that human beings would have had the chance to evolve at all.还有一件事：如果恐龙没有在它们嗅到它的时候嗅到它，那么人类根本不可能有进化的机会。