本文摘要:Scientists have for the first time confirmed liquid water flowing on the surface of present-day Mars, a finding that will add to speculation that life, if it ever arose there, could persist now.科学家首次证实在目前的火星表面有液态水的流动,这一找到令其人们越发开始猜测,如果这个星球上


Scientists have for the first time confirmed liquid water flowing on the surface of present-day Mars, a finding that will add to speculation that life, if it ever arose there, could persist now.科学家首次证实在目前的火星表面有液态水的流动,这一找到令其人们越发开始猜测,如果这个星球上曾多次经常出现生物,那么或许到现在仍有存活。“This is tremendously exciting,” James L. Green, the director of NASA’s planetary science division, said during a news conference on Monday. “We haven’t been able to answer the question, ‘Does life exist beyond Earth?’ But following the water is a critical element of that. We now have, I think, great opportunities in the right locations on Mars to thoroughly investigate that.”“这是十分激动人心的找到,”NASA行星科学部主任詹姆斯·L·格林(James L. Green)在周一的新闻发布会上说道。

“‘地球以外的地方否不存在生物?’这个问题我们尚能无法回答。但对水的跟踪是这种搜索的一个关键。我指出,我们现在近于有可能处在合理的地点,从而回应展开充份的调查。”That marks a shift in tone for NASA, where officials have repeatedly played down the notion that the dusty and desolate landscape of Mars could be inhabited today.这标志着NASA在立场上再次发生改变。

此前他们反复强调,不要过于过期望在这片四起砂砾的荒原上群居着生物。But now, John M. Grunsfeld, NASA’s associate administrator for science, talked of sending a spacecraft in the 2020s to one of these regions, perhaps with experiments to directly look for life.但现在,NASA科学任务指挥官署副局长约翰·M·格伦斯菲尔德(John M. Grunsfeld)回应,有可能在2020年代为首一艘航天器前往其中一个区域,或许不会必要以找寻生物为目的展开一些实验。

“I can’t imagine that it won’t be a high priority with the scientific community,” he said.“这不致是科学界一件头等大事,”他说道。Although Mars had rivers, lakes and maybe even an ocean a few billion years ago, the modern moisture is modest — small patches of damp soil, not pools of standing water.火星在几十亿年前有河流、湖泊甚至有可能有一片海洋,但到了近代那里的湿度很低——只有小块潮湿的土壤,没大片的死水。In a paper published in the journal Nature Geoscience, scientists identified waterlogged molecules — salts of a type known as perchlorates — on the surface in readings from orbit.在一篇刊登于《大自然·地球科学》(Nature Geoscience)的文章中,科学家通过轨道飞行器读数辨识出有火星地表有被曾被水浸没有的分子——一种叫作低氯酸盐的盐类。

“That’s a direct detection of water in the form of hydration of salts,” said Alfred S. McEwen, a professor of planetary geology at the University of Arizona, the principal investigator of images from a high-resolution camera on NASA’s Mars Reconnaissance Orbiter and one of the authors of the new paper. “There pretty much has to have been liquid water recently present to produce the hydrated salt.”“这是必要观测到了以水合盐类形式不存在的水,”亚利桑那大学行星地质学教授阿尔弗雷德·S·麦克尤恩(Alfred S. McEwen)说道,他是NASA火星勘测轨道飞行器高分辨照相机传回图像的首席调查员,也是这篇论文的作者之一。“这基本上证实了在近期有过液态水,从而产生水合盐。”By “recently,” Dr. McEwen said he meant “days, something of that order.”而麦克尤恩说道,所谓“近期”的意思是“几天内,这样一个数量级”。Scientists have long known that large amounts of water remain — but frozen solid in the polar ice caps. There have been fleeting hints of recent liquid water, like fresh-looking gullies, but none have proved convincing.科学家早就告诉在极地冰盖中有大量固态水。

而近期不存在液态水的迹象时有仿佛,比如看起来较新的冲沟,但都不具说服力。In 2011, Dr. McEwen and colleagues discovered in photographs from the orbiter dark streaks descending along slopes of craters, canyons and mountains. The streaks lengthened during summer, faded as temperatures cooled, then reappeared the next year.2011年,麦克尤恩和同事在轨道器传回的图片中找到,在撞击坑、峡谷和山峦下有沿斜坡而下的暗色条纹。这些条纹在夏季不会变大,随着气温上升而慢慢消失,第二年又不会现身。


They named the streaks recurring slope linae, or R.S.L.s, and many thousands of them have now been spotted. “It’s really surprisingly extensive,” Dr. McEwen said.他们将这些条纹命名为“季节性坡纹”,目前早已寻找成千上万处这样的坡纹。“数量之多令人吃惊,”麦克尤恩说道。Scientists suspected that water played a critical role in the phenomenon, perhaps similar to the way concrete darkens when wet and returns to its original color when dry.科学家推断水在这种现象中扮演着了关键角色,或许类似于水泥遇水后颜色变暗,潮湿后又完全恢复原本的颜色。But that was just an educated guess.但那只是基于科学知识的猜测。

Lujendra Ojha, a graduate student at the Georgia Institute of Technology, turned to another instrument on the orbiter that identifies types of molecules by which colors of light they absorb. But this instrument, a spectrometer, is not as sharp as the camera, making it hard to zoom in on readings from the narrow streaks, a few yards across at most.佐治亚理工学院(Georgia Institute of Technology)研究生鲁基恩德拉·欧加(Lujendra Ojha)改用了轨道器上的另一种仪器,根据分子吸取什么颜色的光来辨别分子的类型。但这种叫作光谱仪的仪器没照相机那么低的清晰度,很难将宽度只有几米的较宽放逐大至可以提供数据的程度。“We had to come up with new techniques and novel ways to do analysis of the chemical signature,” said Mr. Ojha, the lead author of the Nature Geoscience article.“我们被迫拿走新的技术和手段来分析其化学特征,”作为《大自然·地球科学》论文第一作者的欧加说道。The researchers were able to identify the telltale sign of a hydrated salt at four locations. In addition, the signs of the salt disappeared when the streaks faded. “It’s very definitive there is some sort of liquid water,” Mr. Ojha said.研究人员在四个地点找到了能解释水合盐不存在的迹象。

此外,当条纹消失时,盐的迹象也不会消失。“可以十分确认那里不存在某种液态水,”欧加说道。The perchlorate salts lower the freezing temperature, and the water remains liquid. The average temperature of Mars is about minus 70 degrees Fahrenheit, but summer days near the Equator can reach an almost balmy 70.低氯酸盐不会减少冰点,让水维持液态。

火星的平均温度约是零下70华氏度(通零下56摄氏度),但夏天在赤道附近的温度可以超过寒冷的70华氏度。Many mysteries remain. For one, scientists do not know where the water is coming from.困惑仍然不存在。

比如科学家不告诉水就是指哪里来的。“There are two basic origins for the water: from above or from below,” Dr. McEwen said. The perchlorates could be acting like a sponge, absorbing moisture out of the air, but measurements indicate very low humidity on Mars — only enough for 10 microns, or about 1/2,500th of an inch, of rain across the planet if all of the wetness were wrung out of the air.“水的来源基本上就是两个,从上面来,或从下面来,”麦克尤恩说道。低氯酸盐能起着海绵的起到,吸取空气里的水分,但勘测表明火星上的湿度很低——假设空气中所有的湿度都被挤出来,那么整个星球的降水仅有为10微米。That idea cannot be ruled out if the lower part of the atmosphere turns out more humid than currently thought.如果大气层的近地部分实质上比目前估算的更加干燥,那么这种水从上面来的可能性是无法回避的。

“We have very poor measurements of relative humidity near the surface,” Dr. McEwen said.“我们对相似地表的相对湿度测量效果很糟,”麦克尤恩说道。The other possibility is underground aquifers, frozen during winter, melting during summer and seeping to the surface.其他的可能性还包括地下含水层,在冬季结冰,到夏季融化,渗透到地表。Liquid water is considered one of the essential ingredients for life, and its presence raises the question of whether Mars, which appears so dry and barren, could possess niches of habitability for microbial Martians.液态水被指出是生命的适当成分,液态水的不存在让人心生疑惑,看起来潮湿而肥沃的火星,不会会不存在微生物版“火星人”的栖息地。

Christopher P. McKay, an astrobiologist at NASA’s Ames Research Center in Mountain View, Calif., does not think the recurring slope linae are a very promising place to look. For the water to be liquid, it must be so salty that nothing could live there, he said. “The short answer for habitability is it means nothing,” he said.在加州山景市NASA艾姆斯研究中心(Ames Research Center)工作的天体生物学家克里斯多弗·P·麦凯(Christopher P. McKay)指出,季节性坡纹并非很有前景的方向。他说道,水要维持液态,盐度就要充足低,那么就没什么东西能存活。

“在适居性方面,非常简单说道就是毫无意义,”他说道。He pointed to Don Juan Pond in Antarctica, which remains liquid year round in subzero temperatures because of high concentrations of calcium chloride salt. “You fly over it, and it looks like a beautiful swimming pool,” Dr. McKay said. “But the water has got nothing.”他提及了南极洲的唐胡安池(Don Juan Pond),由于所含高浓度的氯化钙,那里的水可以在零下的气温下全年维持液态。“你从天上看,它就像个美丽的游泳池,”麦凯说道。


“但那水里什么也没。”Earthly life adapts to many hostile environments, but Don Juan Pond is lifeless.世间的生物可以适应环境许多险恶的环境,但唐胡安池中没生命。Others are not so certain. David E. Stillman, a scientist at the Southwest Research Institute’s space studies department in Boulder, Colo., said water for the streaks might be different in different regions. In some, they form only during the warmest times, suggesting that those waters might not be too salty for microbes.但有的人不像他这么认同。

科罗拉多州博尔德市的西南研究院( Southwest Research Institute)太空研究部科学家戴维·E·斯蒂尔曼(David E. Stillman)说道,在有所不同地区导致条纹的水有可能是有所不同的。有的地方只在温度最低的时候经常出现,指出那些水有可能盐度没有那么低,微生物可以存活。“If it was too salty, they would be flowing year round,” Dr. Stillman said. “We might be in that Goldilocks zone.”“如果盐度太高,它们全年都会是流动的,”斯蒂尔曼说道。“我们有可能处在那个适居拿着。

”Even though recurring slope linae appear to be some of the most intriguing features on Mars, NASA has no plans to get a close-up look anytime soon.季节性坡纹显然是火星上最更有人的特征之一,但NASA不想在近期对其展开近距离的仔细观察。They are treated as special regions that NASA’s current robotic explorers are barred from because the rovers were not thoroughly sterilized, and NASA worries that they might be carrying microbial hitchhikers from Earth that could contaminate Mars.它们被当作类似地区,NASA禁令当前的观测机器人转入,因为这些探测器没有展开过完全消毒,NASA担忧它们离开了地球时装载着的微生物可能会污染火星。Of the spacecraft NASA has sent to Mars, only the two Viking landers in 1976 were baked to temperatures hot enough to kill Earth microbes. NASA’s next Mars rover, scheduled to launch in 2020, will be no cleaner. Sterilizing spacecraft, which requires electronics and systems that can withstand the heat of baking, adds to the cost and complicates the design.在NASA向火星升空的航天器中,只有1976年升空的两艘“维京号”(Viking)着陆器拒绝接受过高温烤制,温度不足以杀掉地球上的微生物。


In selecting the landing site for the 2020 rover, the space agency is ruling out places that might be habitable, including those with recurring slope linae.在为2020年的探测车自由选择降落方位时,NASA回避了有可能合适居住于的地方,还包括有季节性坡纹的地方。That prohibition may continue even though two candidate streaks have been identified on the mountain in Gale Crater that NASA’s Curiosity rover is now exploring, a mile or two from its planned path.尽管已在NASA“奇怪号”探测车正在观测的盖尔陨石坑(Gale Crater)的那座山上找到了两处疑为条纹,前述禁令有可能仍然有效地。

那里距离“奇怪号”的原订路线一两英里。NASA and the Curiosity team could decide to approach the streaks without driving onto them, or to simply observe from a distance. The rover is still probably a couple of years away from them.NASA和“奇怪号”团队可能会要求相似,但不认识那两处条纹,或者只是从远处仔细观察。

探测车有可能仍然还要过几年,才不会超过条纹所在地。NASA officials did not reject the possibility of a detour, although they said it would require analysis and debate.NASA的官员没坚称取道的可能性,但他们回应此事还必须分析和辩论。In an interview after the news conference, Dr. Green of NASA said that if the streaks in Gale Crater turned out to be recurring slope linae, the space agency would consider how great a contamination threat Curiosity, irradiated by ultraviolet light for several years, might pose to a potential Martian habitat.在新闻发布会完结后拒绝接受专访时,来自NASA的格林回应,如果盖尔陨石坑的条纹结果是季节性坡纹,NASA不会考虑到多年拒绝接受紫外线照射的“奇怪号”,可能会给潜在的火星居住于环境导致多大程度的污染威胁。

“If we can go within 20 meters, we can zap it with a laser,” Dr. Green said, referring to an instrument that identifies material inside a rock by the colors of light it emits as it is vaporized. “Then we can learn much more about the details what’s in those R.S.L.s. If we can get closer and actually scoop it up, that would be even better.”“如果去到20米以内的距离,我们就可以用激光去打它,”格林说道。他在这里提及了一种仪器,可以根据石头被气化时收到的光的颜色来辨别里面是什么物质。“然后,我们不会更加理解细节,告诉那些季节性坡纹内部是什么。如果能再行附近一些,实地去挖出一下,效果还要更佳。