美国《国家地理》：外星人如何探测到地球生命？ [美国媒体]

Aliens Could Detect Life on Earth. Here's How.

美国《国家地理》：外星人如何探测到地球生命？



As the universe's only known harbor for life, Earth is arguably one strange rock. But light-years from our solar system, other intelligent beings on a similar planetary oasis might be gazing in our direction and seeing us as a sign that they're not alone in the universe.

作为宇宙中唯一已知的生命港湾，地球可以说是一块奇特的岩石了。但是，在距离我们太阳系光年之外的某个类地行星绿洲上，或许有其他智慧生物正在注视着我们的方向，并将我们地球生命视为他们在宇宙中并不孤单的象征。



Once spotted, our planet would likely intrigue E.T. Our sun is relatively stable, not prone to disastrous flares that'd rip our atmosphere to shreds. What's more, we fall squarely within our sun's habitable zone, the area around a star where liquid water can persist on a planet's surface. (These are just some of the things that make life as we know it possible on Earth.)

一旦被发现，我们的星球可能会激起外星人的兴趣。因为我们的太阳相对稳定，不容易爆发灾难性的耀斑活动，将我们的大气层撕成碎片。更重要的是，我们地球刚好落在太阳系的可居住区内，这个区域处在恒星附近，液态水可以留存于地球表面。（这些只是我们所知道的使地球有可能存在生命的要素。）

Faraway scientists might then attempt to spot our atmosphere, to see whether life's thumb is on the chemical scales. But what would they be looking for? And could they really infer life's presence across trillions of miles?

遥远星球的科学家可能会试图发现我们的大气层，看看在化学层面上是否有生命存在。但他们要找的是什么呢？他们真的能跨越数万亿英里推断出地球生命的存在吗？

Life Is Pretty Gassy

生命跟氧气有很大关系



Terra Cognita?

发现新大陆？

Beyond those chemical clues, alien astronomers with truly massive telescopes might even be able to map Earth's surface from afar, down to major urban areas.

除了这些化学线索之外，外星天文学家拥有真正的大型望远镜，他们甚至可能绘制出地球表面的地图，从偏僻遥远之地覆盖到主要的城市地区。

Advanced Intelligence

高级情报

If intelligent life is nearby, the most straightforward way to find earthlings would be to listen for us. For the last century, human civilization has been broadcasting its existence to the cosmos via our leaky radio transmissions. Occasionally, we've broadcast messages to E.T. intentionally, and sent golden records into the void on the off-chance that aliens stumble across our interplanetary spacecraft.

如果地球附近有智慧生命的话，那么找到地球人最直接的方法就是听到我们的声音。上个世纪，人类文明一直通过无线电传输向宇宙广播我们的存在。偶尔地，我们还会故意向外星人广播信息，将黄金唱片送到太空中播放，希望外星人会无意中偶遇到我们的星际飞船。



Of course, Earth is more than 4.5 billion years old, and life has changed a lot over the eons. What if alien astronomers had looked our way even a billion years ago?

当然了，地球已经有超过45亿年的历史，地球上的生命在亿万年间已经发生了很大的变化。要是外星天文学家们早在十亿年前就已经朝我们的方向看过了呢？

In a 2018 paper in Science Advances, Olson and her colleagues simulated how Earth's atmosphere has changed over time. Even three billion years ago, aliens may have been able to infer life by sniffing out methane and carbon dioxide in the early atmosphere. But our modern atmosphere—a literal beacon for life—arrived only about 500 million years ago.

在《科学进展》杂志2018年的一篇论文中，科学家Olson和她的同事模拟了地球大气层随时间的变化情况。就算外星人在30亿年前就能通过探测早期地球大气中的甲烷和二氧化碳来推断生命是否存在，但现代的地球大气，即真正意义上的生命港湾，也是大约5亿年前才形成的。