10個最有可能發現外星人的地方(上)

Questioning the existence of aliens is something that scientists and average Joes alike have done for decades. Everything from Spielberg's E.T. the Extra-Terrestrial to NASA's latest press releases shows just how large the discussion is and always has been. In fact, most people do believe that aliens exist in some fashion.

近幾十年來，和很多人一樣，科學家們一直懷疑外星人是否存在。從斯皮爾伯格導演的電影《外星人E.T》到NASA發佈的最新消息，都顯示了這一爭論的影響有多大。實際上，大多數人都認爲外星人一定以某種形式存在着。

The main necessities for life are water and some form of energy source. Not surprisingly, there are some planets, exoplanets, and moons that fit the bill. Although we probably won't find little green men with bug eyes, that doesn't make the prospect any less exciting. Here are our 10 best chances at finding life in the universe.

水和某種能量資源是生命存在的必要條件，某些行星、地外行星和衛星能滿足這些條件不足爲奇。雖然可能不會發現長着昆蟲眼睛的綠色小外星人，但人們對發現外星生命的期望值一直居高不下。以下是在宇宙中我們最有可能發現生命的10個地方。

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10.特拉比斯特1號

TRAPPIST-1 is a planetary system a few dozen light-years away whose discovery was announced in early 2017. This system consists of seven Earthlike exoplanets orbiting an "ultra-cool" star, and it is one of our best shots at finding life beyond our own solar system.

2017年初有消息稱發現了一個距地球幾十光年的行星系，這就是特拉比斯特1號。該星系由七顆類地行星組成，環繞一顆“超冷”恆星運轉。在太陽系外，這裏是我們最有機會找到生命的地方之一。

For one thing, studying these exoplanets will be relatively easy because of how they rotate around their star. We can use a telescope to observe their transits, which is when they eclipse their star by passing directly in front of it from our perspective. We see the temporary dimming of the star's light as an exoplanet passes between the star and Earth.

首先，因爲它們圍繞恆星旋轉，研究這些地外行星也就相對容易。我們可以通過望遠鏡來觀測凌日現象，即這些行星從恆星面前穿過並遮擋住恆星。當一顆地外行星從恆星和地球之間穿過，我們能看到恆星短暫的微光。

These exoplanets also have reasonable temperatures due to the nature of their star. So they are cool enough for liquid water to have a chance to form.

由於恆星的性質，這些地外行星溫度適宜，表面的低溫正好有機會生成液態水。

Although all the exoplanets in this system are legitimate candidates to host alien life, three in particular are soundly in what is called the habitable zone. This is the area around a host star where an Earthlike exoplanet is capable of forming liquid water, assuming that all life-forms, like those on Earth, do in fact need water to survive.

儘管該星系中的所有地外行星都可能存在生命，其中分佈在宜居帶內的三顆行星可能性更大。假設所有的生命形式和地球生物一樣，都需要水才能生存的話，宜居帶則是指在一顆主恆星周圍的一定範圍內，至少有一顆能夠形成液態水的類地系外行星。

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9.土衛六

Titan is the largest moon of Saturn, the sixth planet from our Sun. This moon could potentially harbor life but possibly not in the sense that we think. Titan does not exactly fit the description of being in a typical habitable zone.

太陽系八大行星中，土星至太陽距離第六，而土衛六是土星最大的衛星。這顆衛星可能存在生命，但也許不是我們所想的那種生命體，因爲它不完全符合處於宜居帶內這個條件。

Titan has water, and it has liquid. It just doesn't have liquid water. The water on this moon is completely solid because of the extremely cold temperature.

土衛六有水和液態物質，但尚未發現液態水的存在。這顆衛星的超低溫導致水始終保持固態。

However, the liquid that fills the lakes and streams is not water but rather hydrocarbons. A hydrocarbon is a chemical compound of hydrogen and carbon in varying proportions. On Earth, we often think of these as gases like methane or propane.

然而，充斥湖泊、溪谷的與其說是水還不如說是碳氫化合物，這是一種由碳和氫兩種元素以不同比例組成的化合物。在地球上，我們通常認爲它是甲烷或丙烷這樣的氣體。

This is the key factor that would make potential life on Titan so different. Essentially, these life-forms would not survive on liquid water like we do but rather on these liquid hydrocarbons.

這就是土衛六可能存在獨特生命體的關鍵。實質上，這些生命體不會像人類一樣依靠水生存，而是靠這些液態碳氫化合物存活。

Although there are still some technicalities and unanswered questions about science (like if life can live off something other than water), the possibility that Titan has alien life is certainly there.

雖然依舊存在一些技術問題和未解之謎（比如，有的生命體可以依靠水以外的物質生存），但土衛六存在外星生命的可能性極大。

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8.木衛二

Europa is one of Jupiter's moons here in our own solar system. It is another candidate due to its potential to hold liquid water. Europa is thought to have all the necessities for life including water, energy sources, and the right chemical buildup. The water is thought to be stored in oceans underneath Europa's surface.

木衛二是太陽系中木星的衛星之一，有可能存在液態水，因此也有可能存在生命。木衛二被認爲滿足生命存在的所有條件，包括水、能量以及可生成生命的化學物質。有人認爲這些液態水貯存在木衛二地殼下的海洋中。

It wasn't until recently that scientists made it possible to begin the exploration for life on this moon. It was announced in early 2017 that a mission called Europa Clipper would take place over the next several years. This mission is sending a spacecraft to Jupiter's moon to take pictures of the surface. This flyby would happen repeatedly, offering multiple opportunities to analyze the moon and search for life.

直到最近，科學家纔開始對這顆衛星進行探索。2017年初有報道稱，未來幾年內，將開始進行一個名爲“歐羅巴快艇”的探測任務。該任務包括向木衛二發射一艘飛船，並對衛星表面進行拍照。這樣的定點探測會反覆進行，讓我們有機會對木衛二不斷進行分析並探索生命的存在。

7.火星

The Red Planet, the fourth from the Sun, is probably one of the most talked-about potential candidates for extraterrestrial life and even for human colonization. Despite the naysayers, finding extraterrestrial life on Mars really is a serious possibility.

火星是太陽系由內往外數的第四顆行星，這顆紅色行星可能是被談論最多的疑似存在生命的星球，不但有存在地外生命的可能，還有可能實現火星殖民。儘管有人持反對意見，但在火星上找到外星生命的可能性是極大的。

We know by now that we won't find little green men or any intelligent form of life that we understand. However, there is evidence that there was and may still be microscopic life on the small red planet.

如今我們明白，火星上沒有綠色小外星人或是任何我們所瞭解的智慧生命。不過，有證據表明，在這顆紅色小星球上依舊存在微生物。

NASA's data suggests a past presence of floods and streams throughout the dry surface. So there is a chance that liquid water was once on the surface and life could have survived. With further exploration, scientists might find liquid water on Mars presently, instead of just the ice caps that they see today.

美國宇航局有資料顯示，火星乾燥的表面上，留下了洪水和溪流遍佈的古老痕跡。因此火星表面可能存在過液態水，生命有可能因此存活下來。隨着探索的深入，科學家們近期也許能在火星上發現液態水，而不僅僅是他們如今所看到的層層冰帽。

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6.土衛二

Enceladus, another of Saturn's many moons, has the astronomy world abuzz with its potential to hold water, unlike its hydrocarbon-rich sister. The water is supposedly underneath the crust of the moon, similar to Europa.

在土星諸多的衛星中，和那充滿碳氫化合物的兄弟土衛六不同，土衛二作爲又一顆可能存在液態水的星球，引得整個天文界對它衆說紛紜。和木衛二類似，液態水被認爲存在於這顆衛星的地殼之下。

Once again, this would mean that microbes of some kind live there. At first, the presence of water was simply a hypothesis after some evidence found in 2015 gave scientists hope.

同樣，這也意味着存在某些微生物。最開始，土衛二存在水只是一個假設，但2015年發現的一些證據給科學家們帶來了希望。

But in early 2017, a mission involving the Cassini spacecraft detected hydrogen molecules that point to a chemical reaction occurring under the surface. This chemical reaction, in which the ocean water reacts with surrounding rock to produce energy, could be useful to life-forms because an energy source is crucial to life as we know it.

2017年初，一項由“卡西尼號”飛船參與的任務探測到了氫分子，這表明地表下正發生化學反應。衆所周知，能量對生命至關重要，這種由海水與周圍的岩石相互作用而產生能量的化學反應對生命有極大幫助。