為什么在其他行星上尋找生命要依靠氫氣

為什么在其他行星上尋找生命要依靠氫氣

Right now, there are more than 4,000 known exoplanets and plenty of other possible planets that need to be assessed. While we're not going to put human boots on the ground on all these worlds to search for alien life, there are a variety of remote methods to look for current or ancient life.

目前，已知的系外行星有4000多顆，還有很多其他可能的行星需要評估。雖然我們不會為了尋找外星生命而把人類的足跡踏遍所有的星球，但我們可以通過各種各樣的遠(yuǎn)程方法來尋找現(xiàn)代或古代的生命。

We could find life on a planet that has a far different combination of atmospheric gases. (Photo: Jurik Peter/Shutterstock)

Scientists aren't on the lookout for little green men. What astrobiologists and planetary scientists are searching for is akin to the life that developed and flourished for the billions of years before humans even evolved. They're looking for evidence of basic life, like single- or multi-celled organisms on the order of bacteria, viruses, or algae.

科學(xué)家們并不是在尋找小綠人。天體生物學(xué)家和行星科學(xué)家正在尋找的，與在人類進(jìn)化前數(shù)十億年就已經(jīng)發(fā)展和繁榮起來的生命類似。他們正在尋找基本生命的證據(jù)，比如細(xì)菌、病毒或藻類的單細(xì)胞或多細(xì)胞生物。

That other life could be found on planets that have a very different atmosphere than our own. After all, even here, life developed under conditions than would seem strange to us. The younger Earth had less-intense sunlight and a lot more methane in the atmosphere compared to our current oxygen-rich air. Understanding that may be key to finding life elsewhere.

另一種生命可能存在于與我們的大氣層截然不同的行星上。畢竟，即使在這里，生命也是在我們看來陌生的條件下發(fā)展起來的。與我們現(xiàn)在富氧的空氣相比，年輕的地球沒有那么強(qiáng)烈的陽光，大氣中有更多的甲烷。理解這一點(diǎn)可能是在其他地方發(fā)現(xiàn)生命的關(guān)鍵。

"[Our research] is not looking for another Earth per se," Timothy Lyons, a professor in the Department of Earth and Planetary Sciences at the University of California, Riverside told Astrobiology Magazine. Lyons heads up NASA's Alternative Earths team, which gathers information on what we can learn from the early days on this planet to better understand what might support life elsewhere.

加州大學(xué)河濱分校地球與行星科學(xué)系教授蒂莫西·萊昂斯在接受《天體生物學(xué)》雜志采訪時表示:“(我們的研究)并不是尋找另一個地球。”萊昂斯領(lǐng)導(dǎo)著美國國家航空航天局的“替代地球”小組，該小組收集有關(guān)我們能從地球早期了解到的信息，以便更好地理解什么可能支持其他地方的生命。

"It's more about looking for the different pieces of what it is to be a planet that can sustain life. Once you know what those processes do on a planet like Earth, you can assemble them into countless other planetary scenarios that may or may not be able to do the same thing."

“這更多的是尋找一個能夠維持生命的行星的不同部分。一旦你知道這些過程在像地球這樣的行星上發(fā)生了什么，你就可以把它們組合成無數(shù)的其他行星情景，這些情景可能會發(fā)生，也可能不會發(fā)生。”

Why hydrogen-based life is possible

為什么氫基生命是可能的

Looking around our galaxy, most accessible rocky planets are hydrogen-based, but could life develop and survive there? Until we find life on one of these planets, we can't know the answer for sure. But we do know it's possible, according to new research via the Massachusetts Institute of Technology.

環(huán)顧我們的銀河系，最容易找到的巖石行星都是以氫為基礎(chǔ)的，但生命能在那里發(fā)展和生存嗎?直到我們在這些行星中找到生命，我們才能確切地知道答案。但根據(jù)麻省理工學(xué)院的最新研究，我們知道這是可能的。

Perhaps surprisingly, the scientists found that some tough earth-based organisms could survive in a hydrogen-based atmosphere: E. coli (the same as the kind that lives in our gut) and yeast "can survive and grow in a 100% H2 atmosphere," according to the paper in Nature Astronomy.

也許令人驚訝的是，科學(xué)家們發(fā)現(xiàn)一些堅硬的地球生物可以在氫的環(huán)境中生存:大腸桿菌(與生活在我們腸道中的細(xì)菌相同)和酵母“可以在100% H2的環(huán)境中生存和生長”，根據(jù)《自然天文學(xué)》雜志上的文章。

They also found an "astonishing diversity of dozens of different gases produced by E. coli, including many already proposed as potential biosignature gases (for example, nitrous oxide, ammonia, methanethiol, dimethylsulfide, carbonyl sulfide and isoprene)," the paper's authors write.

他們還發(fā)現(xiàn)了“大腸桿菌產(chǎn)生的幾十種不同氣體的驚人多樣性，包括許多已經(jīng)被提出的潛在的生物特征氣體(例如，一氧化二氮、氨、甲硫醇、二甲基硫化物、羰基硫化物和異戊二烯)，”論文的作者寫道。

How atmospheres can reveal possible life

大氣如何揭示可能存在的生命

Knowing which gases could be indicators of hydrogen-based life, or biosignatures, is the key.

關(guān)鍵是要知道哪些氣體可能是氫基生命或生物特征的指示物。

Scientists can do this from Earth by looking at the light that passes through that atmosphere when the planet passes in front of its star. How the light is broken down as it passes through the atmosphere can give details about what's in that atmosphere. Of course, this takes a very powerful telescope, but it's possible.

科學(xué)家們可以從地球上通過觀察當(dāng)行星從其恒星前面經(jīng)過時穿過大氣層的光來做到這一點(diǎn)。光在穿過大氣層時是如何被分解的可以提供關(guān)于大氣層中物質(zhì)的細(xì)節(jié)。當(dāng)然，這需要非常強(qiáng)大的望遠(yuǎn)鏡，但這是可能的。

So if researchers find a hydrogen-based planet, and find the biosignature gases, that could indicate that life exists there. Of course, it's possible that life that evolved on an exoplanet might not give off those specific gases, but it would be a useful clue about where to search if they did.

因此，如果研究人員發(fā)現(xiàn)了一顆以氫為基礎(chǔ)的行星，并發(fā)現(xiàn)了具有生物特征的氣體，那就可能表明那里存在生命。當(dāng)然，在系外行星上進(jìn)化出來的生命可能不會釋放出那些特定的氣體，但如果它們釋放了，這將是一條有用的線索，告訴我們?nèi)ツ睦飳ふ摇?/p>

All of this information isn't a guarantee of where to go and what we might find when we get there, but with over 4,000 planets to consider, it's useful to have a way to narrow down where to start the search for alien life.

所有這些信息并不能保證我們?nèi)ツ睦?，也不能保證當(dāng)我們到達(dá)那里時會發(fā)現(xiàn)什么，但是有超過4000顆行星需要考慮，有一種方法可以縮小尋找外星生命的范圍，這是很有用的。