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有什么人在地球之外吗?

  IN 1990,A year into the journey to Jupiter of an American spacecraft called Galileo,Carl Sagan,a well-known astronomer,turned the probe’s instruments back towards Earth.He wanted to find out whether it was possible to detect evidence of life on the planet from a distance.

  1990年,美国一艘名为伽利略号的宇宙飞船飞向木星一年后,著名天文学家卡尔·萨根将探测器上的仪器转回地球。他想知道是否有可能从远处探测到地球上有生命存在的证据。

  Galileo took spectrographic measurements of sunlight streaming through Earth’s atmosphere and found methane and oxygen,both indicators of living processes.The probe also took photographs of Earth at different wavelengths and uncovered something called the“red edge”—a sharp change in the reflectance of the planet at red wavelengths,which Sagan ascribed to the presence of photosynthetic plant life on the surface.

  伽利略号用光谱仪测量了穿过地球大气层的阳光,发现了甲烷和氧气,这两种都是生命活动的指示物。探测器还拍摄了地球不同波长的照片,并发现了所谓的“红边”——地球在红色波长处反射率的急剧变化,萨根认为这是由于地球表面有进行光合作用的植物的存在。

  There was,however,a third clue—and an indicator that life not only exists on Earth,but has also developed intelligence.This came from the narrowband electromagnetic radiation that was streaming from Earth’s surface—in other words television and radio channels leaking into space.“That,as far as we know,is an unmistakable indicator of technology and an unmistakable indicator of life,”says Andrew Siemion,an astrophysicist at the Berkeley SETI Research Centre in California.“And indeed,it is the most detectable signature of life on this planet as viewed from a distant vantage.”Sagan’s experiment thus confirmed what those engaged in the search for extraterrestrial intelligence(which is what SETI stands for)had suspected—that the best way to find aliens is to look for unnatural radio signals.

  然而,还有第三条线索——它表明生命不仅存在于地球上,而且还发展了智能。这来自于从地球表面流出的窄带电磁辐射,换句话说,是电视和无线电频道泄漏到太空中。加州伯克利SETI研究中心的天体物理学家Andrew Siemion说:“就我们所知,这是一个明确无误的技术指标,也是一个明确无误的生命指标。”的确,从遥远的角度看,这是地球上最容易探测到的生命迹象。因此,萨根的实验证实了那些搜寻地外文明(SETI的缩写)的人的猜测——寻找外星人的最佳方法就是寻找非自然的无线电信号。

  That search is accelerating.As Dr Siemion told this year’s meeting of the American Association for the Advancement of Science(AAAS),in Seattle,better telescopes,faster computers,the discovery of thousands of planets circling stars other than the sun,and an influx of money and scientific talent are transforming the field.What was once a fringe activity has now become mainstream.The next decade,he reckons,will allow astronomers to improve their search for signals from outer space a thousandfold.

  这种搜索正在加速。正如Siemion博士在今年美国科学促进会(AAAS)在西雅图召开的会议上所说,更好的望远镜、更快的计算机、数千颗围绕太阳以外的恒星运转的行星的发现,以及大量资金和科学人才的涌入正在改变着这个领域。曾经的边缘活动现在变成了主流。他认为,在下一个十年里,天文学家们将能够将他们对来自外太空信号的搜索提高一千倍。

  SETI began 60 years ago with Project Ozma.This was led by Frank Drake,an astronomer at Cornell University.It was an attempt to listen for radio waves that might be coming from intelligent life in the vicinity of two nearby sun-like stars,Tau Ceti and Epsilon Eridani.Further projects along this line followed,but no little green men were detected.By the turn of the 21st century people were starting to lose interest and financial support for the endeavour was dwindling.

  SETI始于60年前的奥兹玛计划。这项研究由康奈尔大学的天文学家弗兰克·德雷克领导。这是一次试图监听来自附近两颗类似太阳的恒星Tau Ceti和Epsilon Eridani附近的智能生命的无线电波的尝试。沿着这条路线又有了新的项目,但没有发现小绿人。到了21世纪之交,人们开始对这项努力失去兴趣,对它的财政支持也在减少。

  The tide turned,though,in 2009 with the launch of Kepler,an American probe designed to look for planets orbiting other stars.It found them.In spades.Astronomers have now confirmed the existence of more than 4,000 such exoplanets.Moreover,their models suggest that virtually every star has a planetary system.With so many potential habitats,and more being discovered every month,the prospects of finding alien life suddenly brightened.
纽约时报中英文网 http://www.qqenglish.com/


  2009年,美国发射了旨在寻找围绕其他恒星运行的行星的开普勒号探测器,从而扭转了这一趋势。他们发现。黑桃。天文学家现在已经确认了超过4000颗这样的系外行星的存在。此外,他们的模型表明几乎每颗恒星都有一个行星系。有这么多潜在的栖息地,而且每个月都有更多的发现,发现外星生命的前景突然变得光明起来。

  They will brighten further with the launch,in 2021,of the James Webb Space Telescope and the opening of new observatories on the ground,such as the Extremely Large Telescope(ELT)in Chile.These will be able to repeat,for some nearby exoplanets,the first of Sagan’s experiments with Galileo—the search for biosignatures.But,even if they find them,exciting as that would be,it would say nothing about the crucial final letter in SETI,the“I”for intelligence.

  到2021年,詹姆斯·韦伯太空望远镜的发射和地面上新天文台的建立,如智利的超大望远镜(ELT),将进一步照亮这些行星。对于附近的一些系外行星,这将是萨根对galileo进行的第一次实验——寻找生命特征——的第一次重复。但是,即使他们发现了它们,尽管那将是令人兴奋的,但这也不能说明SETI中至关重要的最后一个字母,即智慧的“我”。

  The search for intelligence was boosted in 2015 with the launch of Breakthrough Listen,a project paid for by Yuri Milner,a software billionaire with a background in physics.This enterprise,on which Dr Siemion is chief scientist,is planned to last ten years and expected to cost$100m.It is intended to survey the 1m nearest stars in detail,scan the entire plane of Earth’s home galaxy,the Milky Way,and also listen for messages from the 100 closest galaxies.It is paying for astronomers interested in SETI to have time on more than a dozen big radio observatories around the world,and it collects in a day an amount of data that used previously to take a year to gather.

  2015年,随着有物理学背景的软件亿万富翁尤里·米尔纳出资的“突破聆听”项目的推出,对智能的探索得到了提升。Siemion博士是该项目的首席科学家,该项目计划持续10年,预计耗资1亿美元。它的目的是详细调查离我们最近的1百万颗恒星,扫描地球的母星系——银河系的整个平面,并监听来自离我们最近的100个星系的信息。它为那些对SETI感兴趣的天文学家提供资金,让他们有时间在世界各地的十几个大型射电天文台上进行观测,并在一天之内收集到以前需要一年才能收集到的大量数据。

  Nor is Breakthrough Listen alone.On February 13th the SETI Institute,a not-for-profit organisation in California,and America’s National Radio Astronomy Observatory,announced a collaboration.The observatory operates the Very Large Array(VLA),a radio telescope in New Mexico that features in the film“Contact”.The collaboration allows SETI researchers to tap the entire stream of data the VLA records as it carries out its routine experiments.

  突破不仅仅是听。2月13日,位于加州的非营利组织SETI研究所和美国国家射电天文台宣布了一项合作计划。该天文台运行着甚大阵(VLA),这是一架位于新墨西哥州的射电望远镜,电影《接触》中使用了它。这项合作使得SETI的研究人员可以在VLA进行常规实验时,利用VLA记录的整个数据流。 纽约时报中英文网 http://www.qqenglish.com

  The partnership will become even more useful for SETI researchers if the VLA gets a proposed upgrade that would greatly enhance its sensitivity.This next-generation instrument would be good enough to detect electromagnetic radiation leaking from planets,similar to the television and radio channels that Sagan measured leaking from Earth.

  如果VLA得到拟议的升级,将大大提高其灵敏度,这种合作关系将对SETI的研究人员更加有用。这个新一代的仪器将足以探测到从行星泄漏的电磁辐射,类似于萨根测量到的从地球泄漏的电视和无线电频道。

  尽管无线电波很重要,未来的SETI搜索也不会停留在这一波段

  Nor,despite the importance of radio waves,will future SETI searches stick to that part of the spectrum.Alien civilisations might,for example,use laser flashes as optical beacons to signal their presence.If a nanosecond-long pulse of such light were pointed in the direction of Earth,it could be made energetic enough to seem brighter to human instruments than any of the stars in the same part of the sky.

  尽管无线电波很重要,未来的SETI搜索也不会停留在这一波段。例如,外星文明可能使用激光作为光信标来表明他们的存在。如果这种光的一个毫微秒长的脉冲指向地球的方向,就可以使它具有足够的能量,在人类仪器看来,它比天空同一区域的任何星星都要亮。

  Moreover,as observatories get better,astronomers will also be able to spot small,potentially pertinent features in and around exoplanets.These might be rings of satellites above a planet’s equator—or even structures surrounding a planetary system’s star,put there to capture that star’s light as a source of energy.

  此外,随着天文台的改进,天文学家也将能够发现系外行星及其周围的微小的、可能相关的特征。这些可能是一颗行星赤道上方的卫星环,或者甚至是围绕着一颗行星系统的恒星的结构,用来捕获该恒星的光作为能量来源。

  一个足够大的空间站,也可以用类似于观测系外行星的方法探测到

  Even a single space station,were it big enough,might be detectable using methods similar to those employed to spot exoplanets.A space station the size of Earth’s moon(admittedly,a huge space station)would stop enough of the light of its star from reaching Earth to produce a perceptible dip in that light.This“transit”method is how Kepler spotted its prey and,as instruments improve,should one day be sensitive enough to spot exomoons too.The way to tell the difference between a moon and a moon-sized space station,says Dr Siemion,would be that the former would orbit regularly whereas the latter might be able to move around at will.

  即使是一个足够大的空间站,也可以用类似于观测系外行星的方法探测到。一个月球大小的空间站(诚然,一个巨大的空间站)将会阻止足够多的恒星光线到达地球,从而使光线产生明显的倾斜。这种“凌日”方法就是开普勒发现它的猎物的方法,随着仪器的改进,有朝一日它也会足够灵敏地发现外行星。Siemion博士说,区分月球和月球大小的空间站的方法是,前者会有规律地绕轨道运行,而后者可以随意移动。

  More standard searches for chemical biosignatures could also be useful for SETI.A system of particular interest is Trappist-1,40 light-years from Earth,where seven rocky worlds orbit a red dwarf.Three of these are within the star’s“habitable zone”—a region where planets could have liquid water on their surfaces.

  对化学生物特征的更多标准搜索也可能对SETI有用。一个特别有趣的系统是Trappist-1,距地球40光年,在那里有七个由岩石组成的星球围绕着一颗红矮星运行。其中三个位于该恒星的“宜居带”内——行星表面可能有液态水的区域。

  The next generation of instruments will reveal whether the planets in Trappist-1 have atmospheres or oceans.If there are atmospheres,they will also reveal what gases are within them—possibly showing biosignatures of the sort Sagan spotted on Earth.

  下一代的仪器将揭示Trappist-1中的行星是否有大气或海洋。如果存在大气层,它们也将揭示其中的气体——可能显示出萨根在地球上发现的那种生物特征。

  Meanwhile,the Breakthrough Listen dataset continues to grow.In a study discussed in Seattle,a team of astronomers used it to look for radio transmissions from 20 stars in the so-called“Earth transit zone”—the part of the sky from which Earth itself would be detectable by the transit method.The hypothesis is that,if intelligent beings do exist in that region,they might thus have discovered Earth and be aiming transmissions at it.So far,the skies have been quiet.But SETI researchers are patient people.And they live in hope.

  与此同时,突破性的监听数据集继续增长。在西雅图进行的一项研究中,一组天文学家用它来寻找所谓的“地球凌日带”中的20颗恒星发出的无线电信号。“地球凌日带”是天空的一部分,通过凌日法可以探测到地球本身。他们的假设是,如果该地区确实存在智能生命,他们可能因此发现了地球,并将信息传送到那里。到目前为止,天空一直很平静。但是SETI的研究人员是有耐心的人。他们生活在希望中。
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