BBC News: 火星上现在或者曾经有过生命吗?

Is, or was there ever, life on Mars? It's a question that's excited scientists since the dawn of the space age. And right now, there are orbiters, landers, roving vehicles all over the surface of the red planet, analyzing it. But it's still an open question: how habitable is our celestial neighbor and what, if anything, could have inhabited it? Here are four key moments in the search to answer that question: In 1976, NASA's 'Viking' lander, was the first mission to look for microbial life in soil samples it grabbed from Mar's surface. It didn't find evidence of even the simplest, organic molecule. Since then, some members of the Viking team have questioned whether they missed something in that initial analysis. But to this day, there's no accepted evidence of microbial life on Mars.

In July of 1996, NASA scientists announced the discovery of fossils of bacterial life in meteorites that they found in Antarctica—meteorites from Mars that had crashed into our planet12,000 years ago. After huge, initial excitement, NASA said that after two years of continuing to study that meteorites, those initial lines of evidence simply went away. But to this day, there are still scientists who maintain that initial analysis was valid. Both NASA's 'Curiosity' rover and the European Space Agency's orbiter have detected whiffs of the gas methane on Mars. Now that's tantalizing because on Earth, the vast majority of methane comes from microbial life so future martian missions have set their sights on detecting exactly where that gas is coming from. Most recently, and possibly most excitingly, researchers have found the first evidence of an existing body of liquid water on Mars. It was found using radar and this is a sub-glacial lake under the southern polar ice cap of the red planet.

火星上现在或者曾经有过生命吗?自从人类进入太空时代，这个问题就刺激着科学家们的神经。当前，轨道飞行器、着陆器和探测车都在这颗红色星球的表面进行分析。但是这仍然是一个没有解决的问题：我们的星球邻居到底有多适合人类居住?如果可能，又有什么适合居住?在研究中有四个关键性的事件可以回答这个问题：1976年，美国宇航局的“海盗号”着陆器寻找其从火星表面上采集的土壤样品中是否有微生物，这是探测火星是否存在生命的第一个飞行器。它没有发现哪怕是最简单的有机分子的证据。自那以后，“海盗号”团队的一部分成员就质疑在最初的分析中他们是否遗漏了一些东西。但是直到今天，没有可以接受的证据表明火星上存在微生物。1996年7月，美国宇航局科学家宣布他们在南极的火星陨石里发现了细菌化石，这些陨石是1万2千年前从火星坠落到地球上的。在经历了最初的巨大惊喜后，美国宇航局表示经过两年对这些陨石持续不断的研究，那些证明存在细菌的最初的线条已经消失了。但是直到今日，仍然有科学家认为那些最初的分析是有效的。美国宇航局的“好奇号”火星探测器和欧洲航天局的轨道飞行器都探测到火星上存在甲烷气体。这一点令人兴奋，因为在地球上，绝大部分甲烷来自微生物，所以未来火星的探测任务将会把目标锁定在精确探测这些甲烷气体来自于火星哪里。在刚刚过去的不久前，出现了可能是最令人兴奋的一次发现，研究人员发现了火星上有液态水存在的第一个实体证据。它是由雷达发现的火星南极冰盖下的一个冰下湖。