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.
近几十年来，和很多人一样，科学家们一直怀疑外星人是否存在。从斯皮尔伯格导演的电影《外星人E.T》到NASA发布的最新消息，都显示了这一争论的影响有多大。实际上，大多数人都认为外星人一定以某种形式存在着。
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.
水和某种能量资源是生命存在的必要条件，某些行星、地外行星和卫星能满足这些条件不足为奇。虽然可能不会发现长着昆虫眼睛的绿色小外星人，但人们对发现外星生命的期望值一直居高不下。以下是在宇宙中我们最有可能发现生命的10个地方。
10.特拉比斯特1号
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年初有消息称发现了一个距地球几十光年的行星系，这就是特拉比斯特1号。该星系由七颗类地行星组成，环绕一颗“超冷”恒星运转。在太阳系外，这里是我们最有机会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，因为它们围绕恒星旋转，研究这些地外行星也就相对容易。我们可以通过望远镜来观测凌日现象，即这些行星从恒星面前穿过并遮挡住恒星。当一颗地外行星从恒星和地球之间穿过，我们能看到恒星短暂的微光。
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.
由于恒星的性质，这些地外行星温度适宜，表面的低温正好有机会生成液态水。
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.
尽管该星系中的所有地外行星都可能存在生命，其中分布在宜居带内的三颗行星可能性更大。假设所有的生命形式和地球生物一样，都需要水才能生存的话，宜居带则是指在一颗主恒星周围的一定范围内，至少有一颗能够形成液态水的类地系外行星。
9.土卫六
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.
太阳系八大行星中，土星至太阳距离第六，而土卫六是土星最大的卫星。这颗卫星可能存在生命，但也许不是我们所想的那种生命体，因为它不完全符合处于宜居带内这个条件。
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.
土卫六有水和液态物质，但尚未发现液态水的存在。这颗卫星的超低温导致水始终保持固态。
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、溪谷的与其说是水还不如说是碳氢化合物，这是一种由碳和氢两种元素以不同比例组成的化合物。在地球上，我们通常认为它是甲烷或丙烷这样的气体。
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.
这就是土卫六可能存在独特生命体的关键。实质上，这些生命体不会像人类一样依靠水生存，而是靠这些液态碳氢化合物存活。
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.
虽然依旧存在一些技术问题和未解之谜（比如，有的生命体可以依靠水以外的物质生存），但土卫六存在外星生命的可能性极大。
8.木卫二
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.
木卫二是太阳系中木星的卫星之一，有可能存在液态水，因此也有可能存在生命。木卫二被认为满足生命存在的所有条件，包括水、能量以及可生成生命的化学物质。有人认为这些液态水贮存在木卫二地壳下的海洋中。
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，科学家才开始对这颗卫星进行探索。2017年初有报道称，未来几年内，将开始进行一个名为“欧罗巴快艇”的探测任务。该任务包括向木卫二发射一艘飞船，并对卫星表面进行拍照。这样的定点探测会反复进行，让我们有机会对木卫二不断进行分析并探索生命的存在。
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.
火星是太阳系由内往外数的第四颗行星，这颗红色行星可能是被谈论最多的疑似存在生命的星球，不但有存在地外生命的可能，还有可能实现火星殖民。尽管有人持反对意见，但在火星上找到外星生命的可能性是极大的。
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.
如今我们明白，火星上没有绿色小外星人或是任何我们所了解的智慧生命。不过，有证据表明，在这颗红色小星球上依旧存在微生物。
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.
美国宇航局有资料显示，火星干燥的表面上，留下了洪水和溪流遍布的古老痕迹。因此火星表面可能存在过液态水，生命有可能因此存活下来。随着探索的深入，科学家们近期也许能在火星上发现液态水，而不仅仅是他们如今所看到的层层冰帽。
6.土卫二
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.
在土星诸多的卫星中，和那充满碳氢化合物的兄弟土卫六不同，土卫二作为又一颗可能存在液态水的星球，引得整个天文界对它众说纷纭。和木卫二类似，液态水被认为存在于这颗卫星的地壳之下。
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.
同样，这也意味着存在某些微生物。最开始，土卫二存在水只是一个假设，但2015年发现的一些证据给科学家们带来了希望。
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，一项由“卡西尼号”飞船参与的任务探测到了氢分子，这表明地表下正发生化学反应。众所周知，能量对生命至关重要，这种由海水与周围的岩石相互作用而产生能量的化学反应对生命有极大帮助。
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