BBC News: 火星上現在或者曾經有過生命嗎?

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.

火星上現在或者曾經有過生命嗎?自從人類進入太空時代，這個問題就刺激著科學家們的神經。當前，軌道飛行器、著陸器和探測車都在這顆紅色星球的表面進行分析。但是這仍然是一個沒有解決的問題：我們的星球鄰居到底有多適合人類居住?如果可能，又有什么適合居住?在研究中有四個關鍵性的事件可以回答這個問題：1976年，美國宇航局的“海盜號”著陸器尋找其從火星表面上采集的土壤樣品中是否有微生物，這是探測火星是否存在生命的第一個飛行器。它沒有發(fā)現哪怕是最簡單的有機分子的證據。自那以后，“海盜號”團隊的一部分成員就質疑在最初的分析中他們是否遺漏了一些東西。但是直到今天，沒有可以接受的證據表明火星上存在微生物。1996年7月，美國宇航局科學家宣布他們在南極的火星隕石里發(fā)現了細菌化石，這些隕石是1萬2千年前從火星墜落到地球上的。在經歷了最初的巨大驚喜后，美國宇航局表示經過兩年對這些隕石持續(xù)不斷的研究，那些證明存在細菌的最初的線條已經消失了。但是直到今日，仍然有科學家認為那些最初的分析是有效的。美國宇航局的“好奇號”火星探測器和歐洲航天局的軌道飛行器都探測到火星上存在甲烷氣體。這一點令人興奮，因為在地球上，絕大部分甲烷來自微生物，所以未來火星的探測任務將會把目標鎖定在精確探測這些甲烷氣體來自于火星哪里。在剛剛過去的不久前，出現了可能是最令人興奮的一次發(fā)現，研究人員發(fā)現了火星上有液態(tài)水存在的第一個實體證據。它是由雷達發(fā)現的火星南極冰蓋下的一個冰下湖。