For lifeless chemical compounds to organize themselves into something alive, scientists generally agree, three sets of things must be present:
科学家基本公认，无生命的化学物质自行组合形成生命，需要具备三个前提条件：
■ Standing water and an energy source.
■ 静态水和能量来源。
■ Five basic elements: carbon, oxygen, hydrogen, phosphorus and nitrogen.
■ 五种基本元素：碳、氧、氢、磷和氮。
■ And time, lots of time.
■ 还有时间，漫长的时间。

In its search for environments where life might have started on Mars, the Curiosity rover has found the standing water, the energy and the key elements with the right atomic charges. As a result, scientists have concluded that at least some of the planet must have been habitable long ago.
在寻找火星上适宜生命的环境的过程中，“好奇号”火星探测车找到了静态水、能源和原子电量正好合适的基本元素。据此，科学家得出结论，火星上至少有些地方在很久以前是适宜生命存在的。
But the period when all conditions were right was counted in hundreds to thousands of years, a very small opening by origin-of-life standards.
但在火星历史上，所有这些条件都具备的时间跨度大约是几百到几千年，而以生命起源的标准衡量，那实在不过是转瞬之间。
That has now changed. John P. Grotzinger of Caltech, the project scientist for the mission, reported at a news conference on Monday that the rover’s yearlong trek to Mount Sharp provided strong new evidence that Gale Crater had large lakes, rivers and deltas, on and off, for millions to tens of millions of years. The geology shows that even when the surface water dried up, plenty of water would have remained underground, he said.
不过，现在有了新发现。负责“好奇号”火星项目的加州理工科学家约翰·P·格罗青格(John P. Grotzinger)周一（12月8日——译注）在新闻发布会上宣布，“好奇号”向着夏普峰历时一年的跋涉发现了有力的新证据，证明盖尔环形山曾有大型湖泊、河流和三角洲，而且这些地貌断断续续存在的时间有数百万到数千万年之间。他说，已知的火星地理特征说明，即使是在地表水干涸的时候，也有地下水存在。
Moreover, the team concluded, numerous deltalike and lakelike formations detected by orbiting satellites are almost certainly the dried remains of substantial ancient lakes and deltas. None of this proves that life existed on the planet, but the case for an early Mars that was ripe and ready for life has grown stronger.
此外，科学家团队还得出结论，环绕火星的卫星发现大量类三角洲或类湖泊地貌，几乎可以肯定就是古代湖泊和三角洲干涸之后的遗迹。这些均不能证明火星上曾有生命，但早期火星适宜生命存在的可能性极大地增强了。
“As a science team, Mars is looking very attractive to us as a habitable planet,” Dr. Grotzinger said in an interview. “Not just sections of Gale Crater and not just a handful of locations, but at different times around the globe.”
“对于我们科学团队来说，火星作为一个生命宜居行星，显得十分诱人，”格罗青格说。“不仅是在盖尔环形山，也不仅是有限几个地点，而是在不同历史时期遍布火星各处。”
And John M. Grunsfeld, a former astronaut who is NASA’s associate administrator for science, said that after almost 28 months on Mars, Curiosity has given scientists insight into how and where to look for clues of ancient life. “We don’t know if life ever started on Mars, but if it did, we now have a better chance of discovering it” on future missions, he said.
美国国家航空航天局(NASA)科学副总监、前宇航员约翰·M·格伦斯菲尔德(John M. Grunsfeld)也说，“好奇号”在火星的近28个月让科学家学到很多东西，知道该怎样寻找古代生命的线索，以及到哪里去找。“我们不知道火星上是否曾有生命起源，但如果有的话，我们[在今后探索任务中]发现它的机会更大了，”他说。
Another missing piece of the story has been the inability to detect organic compounds — the carbon-based building blocks of life.
探索生命起源的过程中另一个缺失的环节是一直没有找到有机化合物——构成生命的碳基元件。
That too may soon change. Last spring, several Curiosity team members reported the detection of some simple organics that appeared to be Martian. The findings were not definitive, but NASA has scheduled a news conference Dec. 14 at the annual meeting of the American Geophysical Union with “new information” about the search for organics. “Our original interpretation — that there was a good chance the organics we were seeing are Martian — hasn’t changed,” said Daniel P. Glavin of the Goddard Spaceflight Center, an author of the earlier paper. “This interpretation will be expanded on at A.G.U.”
这一点也可能很快会有突破。今年春季，“好奇号”的几位科学家报告发现了可能是火星上的某些简单有机物。这个发现没有遽下结论，但航天局已经安排了12月14日在美国地球物理学会(American Geophysical Union)年会上召开新闻发布会，发布关于探索火星有机物的“新消息”。那篇论文的作者之一、戈达德航天中心(Goddard Spaceflight Center)的丹尼尔·P·格莱文(Daniel P. Glavin)说：“我们最初的解读——很可能我们发现的就是火星有机物——并没有改变。在AGU年会上我们会进一步介绍。”
Curiosity does not carry life-detection instruments, in large part because there is no consensus on what such an instrument might be. A finding of life based on what at first appeared to be metabolic activity, detected during the Viking missions of 1977, was so controversial that NASA ultimately rejected it. So scientists have been using a variety of tools — from geology and other earth sciences, organic and mineral chemistry, atmospheric measurements and sophisticated cameras — to determine whether life could have arisen and survived in Gale Crater and other locations with similar characteristics.
“好奇号”没有搭载生命探测设备，主要是因为究竟该用什么样的设备，科学家没有达成共识。1977年“海盗号”探测器报告发现了生命迹象，基于的是一开始被认为是代谢行为的现象。但那次发现争议很大，航天局最终做出了否定判断。因此，科学家开始用各种工具——包括地质学等地球科学的工具、有机和无机化学、大气探测以及精密摄像机等等——去判断盖尔环形山和其他类似地点是否曾经有生命出现并存活。
Another member of the Curiosity team, Roger Summons of M.I.T., says that findings from that rover and previous missions suggest that early Mars may have been quite similar to early Earth.
“好奇号”团队的另一名成员、麻省理工的罗杰·萨曼斯(Roger Summons)说，“好奇号”和历史上其他的火星探索显示，早期火星或许和早期地球十分相近。
For the first billion years, he said, both planets had stable environments that could support life for substantial periods, and both still share the same chemistry and processes for altering rocks. There is a general scientific consensus that life began on Earth some 3.8 billion years ago, and Dr. Summons said it was clear that the same could have happened on Mars. Or as Dr. Grunsfeld put it, “What I get excited about is imagining a Mars 3.5 to 4 billion years ago, a planet with a thick atmosphere, maybe a blue sky with puffy clouds and mountains and lakes and rivers.”
他说，最初的10亿年，两个星球都有稳定的环境，允许生命在相当长的时间里存在。直到今天，地球和火星仍然有相同的化学构成以及促使岩石发生转变的地质过程。科学界基本同意，生命在地球上开始于大约38亿年前。萨曼斯称，很明显同样的事情可能也发生在火星上。或者像格伦斯菲尔德说的那样：“让我激动的是想像一个35到40亿年前的火星，一个包裹在厚厚的大气层中的星球，可能有蓝天白云，有山脉、湖泊和河流。”
Many similarities disappeared after Mars, a much smaller planet, lost much of its protective atmosphere by the end of its first billion years. So searching for possible Martian life involves digging deep below the surface or detecting microbial remains billions of years old. Identifying ancient microbial life has proved extremely difficult and controversial on Earth, and the challenge on Mars is considerably greater.
在它基本度过第一个10亿年的时候，火星这颗小得多的行星丧失了大部分保护它的大气层，于是很多相似性也消失了。因此，搜寻火星生命就需要深深地挖掘地表下岩层，或者探测几十亿年前的微生物遗迹。在地球上辨识古代微生物极其困难，而且也难令所有人信服；在火星上，这种挑战就更大了。
For that reason, scientists have long called for a mission to bring rock and soil samples back to Earth for sophisticated analysis. The Mars mission scheduled for 2020 would begin the effort by experimenting with methods to select, lift and store promising samples.
因此，科学家一直呼吁把火星岩石和土壤样本带回地球做深入分析。2020年开始的火星计划将开始尝试挑选、提取和储存有希望的样本。
But there are no Mars samples now — except those that arrive as long-traveling meteorites — so astrobiologists have to conduct their search for life using other methods and teasing out hidden evidence.
但是目前还没有火星样本——除了长途飞行来到地球的陨石——因此，宇宙生物学家只能用其他方法进行寻找生命的工作，梳理出隐藏的线索。
The search for water on Mars, for instance, goes back decades and many missions. But scientists were never certain that the carved canyons and deltas were results of water running long ago, or perhaps lava or frozen carbon dioxide. Because of Curiosity, there is now a wide consensus that early Mars had much water.
比如，寻找火星水的工作在几十年前的火星计划中就开始了。但科学家一直不能肯定，那些大峡谷和三角洲究竟是古代河流冲刷形成的，还是熔岩或冻结的二氧化碳造成的。多亏了“好奇号”，现在科学家普遍同意，早期火星上有很多水。
This conclusion has been difficult to square with climate models, which point to a colder early Mars with a thin atmosphere that could not have supported large bodies of standing water, or rivers that ran for millions of years. But faced with mounting evidence of longstanding water and consequently warmer conditions, the climate scientists have gravitated toward two interwoven explanations — both with implications for early life.
这个结论一度很难在火星气候模型中说得通。火星气候模型显示，早期火星冰冷，大气稀薄，不支持大量静态水的存在，不可能有流淌了几百万年的河流。但面对越来越多的关于持续存在的水源和由此导致的温暖环境的证据，气候学家开始倾向于两种互相交叉的解释——两种解释都意味着可能有早期生命存在。
The first is that frequent volcanoes and meteorite impacts heated the planet substantially; volcanoes also emit gases known to synthesize into organic compounds. The second is that to explain the substantial water cycle required to keep many Martian lakes filled and rivers flowing, the planet needed a substantial ocean in its northern half. Large swaths of Mars north of its equator are one to three miles lower than the so-called southern highlands, and scientists have proposed that an ocean may have filled and molded the vast depression. Others disagree on several grounds, including that no remnant shoreline has been detected.
第一种解释是，频繁的火山活动和陨石撞击让星球大幅升温；火山也会释放出气体，能合成有机化合物。第二个解释是，火星要维持水循环，让火星湖泊和河流成为可能，那么在北半球就应该有一大片海洋。火星赤道以北的大片区域比通称的南方高地要低一到三英里。科学家提出假设，北半球可能有古代海洋，塑造了广袤的低地。也有人不同意，基于好几条理由，包括没有探测到海岸线的遗迹。
“We don’t have hard evidence of a northern ocean, but our models require that much water to explain what the geologists have now confirmed,” said Michael A. Mischna of the Jet Propulsion Laboratory, another Curiosity team member. “What Curiosity has done is to bring together atmospheric and climate information with the findings of the geologists and geochemists, and created a broad and consistent story of a very wet early Mars.”
“我们没有发现北半球海洋的确凿证据，但我们的模型要求有一大片水体，这样才能解释目前地质学家已经证实的结论，”“好奇号”团队成员、喷气推进实验室(Jet Propulsion Laboratory)的迈克尔·A·米什纳(Michael A. Mischna)说。“好奇号的工作就是将大气与气候信息，和地质学家与地质化学家的发现整合起来，构建一个大跨度、可以自圆其说的理论，描述一个非常湿润的早期火星。”
While the evidence for water has become increasingly clear, the question of organic compounds is in flux. Such chemicals fall onto Mars all the time in interstellar dust and meteorites, as they do onto Earth. Yet none have been definitively detected.
关于水的证据已经越来越清楚了，但有关有机化合物的疑问还有一大堆。这类物质不断以星际尘埃和陨石的形式落到火星上，就像落在地球上一样，但目前还从来没有被确凿地发现。
But on this mission, team members knew to look for a salt called perchlorate that has been demonstrated on Earth to destroy or transform organics in the presence of heat. Substantial amounts of perchlorate were found in Gale Crater, suggesting that if early Mars had organic chemicals and they survived eons of radiation bombardment, they are long since gone or they will remain very difficult to detect with current techniques.
不过在这次火星探索中，科学家知道应该寻找一种叫做高氯酸盐的无机物。在地球上，高氯酸盐被证明可以在高温下破坏有机物，或者促使有机物转化。在盖尔环形山上发现了大量高氯酸盐。这意味着，如果早期火星存在有机物，而且它们没有被持续的宇宙辐射消灭，那么它们现在也早就不存在了，或者用现有的技术很难发现。
The Sample Analysis at Mars instrument is designed to identify relatively simple organics that burn off as gases in its oven. But it also carries nine cups with a solvent that can alter more complex molecules (like amino acids and nucleic acids) in ways that protect their signature.
火星样本分析设备是用来识别相对简单的有机物的。这些有机物将在它的烤炉内作为气体燃尽。但它也带有九个杯子，盛着一种溶剂，可以转化更复杂的分子（比如氨基酸和核酸）同时保护它们的化学特征。
This “wet chemistry” has been awaiting the finding of a sample rich in organics. A further problem is that one of its cups leaked, causing enormous headaches and making team leaders wary.
这种“湿化学”技术一直还在等待富含有机物的样本被发现。另一个问题是设备的其中一只杯子发生了泄漏，制造了大麻烦，让团队负责人不放心。
But Dr. Glavin, a member of the team, hopes the spilled solvent will itself be used to test previously collected Martian samples, making it the first wet-chemistry experiment ever on another planet.
但团队成员格莱文希望，溢洒的溶剂可以被用来测试之前采集的火星样本，那将是外星球进行的第一次湿化学试验。
Clearly, the search for life on Mars — past or present — will be neither straightforward nor swift.
很显然，寻找火星生命——无论是古代生命还是现今的生命——不会是一帆风顺，也不可能马上成功。