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博主胡德良:邢台学院外语系英语教授,中国译协专家会员,河北省译协常务理事,邢台市译协副会长。爱好翻译,内容涉及宇宙探秘、医疗卫生、家庭保健、生命科学、能源科学、地球科学、环境科学、散文小说和纪实文学等领域。所译文章曾见于《光明日报》、《科技日报》、《健康时报》、《健康报》、《英语世界》、《英语知识》、《科技英语学习》、《科学之友》、《科学与文化》、《世界科学》、《生命世界》等全国各大报刊。博客特色:英汉对照、图文并茂,融趣味性、科学性、知识性为一体。

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矮星周围七颗潜在的宜居类地行星(图)   

2017-08-19 07:16:05|  分类: 宇宙探秘 |  标签: |举报 |字号 订阅

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矮星周围七颗潜在的宜居类地行星(图) - 月亮飞船 - 欢迎光临月亮飞船的博客
 七颗地球大小的行星在一颗被称为
TRAPPIST-1的暗淡矮星之前经过。
矮星周围七颗潜在的宜居类地行星(图) - 月亮飞船 - 欢迎光临月亮飞船的博客
TRAPPIST-1系统中行星的大小可能相当于地球,但是作为一个系统,它更像木星及其最大的几颗卫星。
胡德良   译

Astronomers announced today the discovery of an extraordinary planetary system: seven Earth-sized planets that could all have liquid water on their rocky surfaces. The planets circle a tiny, dim, nearby star in tight orbits all less than 2 weeks long. Although it isn’t possible today to say whether the planets harbor life, astronomers are excited because each planet’s orbit passes in front of—or “transits”—its parent star. What’s more, the system’s proximity to Earth means that answers to questions about whether the system is habitable may come in just a few years’ time with the launch of a powerful new space telescope. 

 天文学家们今天宣布,他们发现了一个非同寻常的行星系统——有七颗地球大小的行星,它们的岩石表面上都可能含有液态水。这些行星围绕着一颗附近的暗淡小恒星运转,轨道紧凑,公转周期均不到两周。虽然目前还不可能说清这些行星上是否拥有生命,但是天文学家们感到很兴奋,因为每颗行星的轨道都经过主恒星的前面——或称为“凌日”。此外,该行星系统与地球的相似程度较高,这意味着:随着功能强大的新型太空望远镜发射升空,该系统是否适于居住的问题可能在几年的时间内就有答案了。

 “If we are to find a biosignature, it may be in this kind of system,” says astrophysicist Nikku Madhusudhan of the Institute of Astronomy in Cambridge, U.K., who was not involved in the study. “In terms of transiting planets, this is as close to the holy grail as we’ve ever seen.” Team member Didier Queloz of the University of Cambridge says that the system, known as TRAPPIST-1, will be “a major driver of the question of whether there is life in the universe.” Says Thomas Henning, director of the Max Planck Institute for Astronomy in Heidelberg, Germany: “Imagine a solar system with seven planets like our own, it’s just amazing.”

 英国剑桥天文学研究所的天体物理学家尼库·马杜苏丹说:“如果我们要想发现某种生物特征,那么这种特征可能就存在于这样的系统中。从凌日行星的角度来说,这是我们所观察到的距离最近的系统了,很珍贵。”马杜苏丹没有参加这项研究。剑桥大学的研究小组成员迪迪埃·奎洛兹称:“在研究宇宙中到底是否拥有生命的问题上,这个被称为‘TRAPPIST-1’的系统将成为研究人员的主要研究动力。”德国海德尔堡市马普学会天文学研究所所长托马斯·亨宁说:“想象一下,一个恒星系统中拥有7颗类似我们地球的行星……太奇妙了!”

 Many exoplanets searches have focused on sunlike stars in the hopes of finding an analog to our own solar system—unsurprising because it is the one system known to foster life. But the team behind the Belgium-led TRAPPIST project (Transiting Planets and Planetesimals Small Telescope) took a different tack: They looked for planets that transit in front of dim, dwarf stars, by far the most numerous type of star in the Milky Way. Starting in 2010 with a 0.6-meter robotic telescope at the European Southern Observatory’s (ESO’s) La Silla Observatory in Chile, they quickly came across the star that came to be known as TRAPPIST-1.

 许多系外行星的寻找活动都集中于类日恒星,希望发现与我们太阳系类似的恒星系统。这一点也不奇怪,毕竟太阳系是可以促进生命发育的已知星系。然而,由比利时领导的“TRAPPIST(小型凌日行星和微行星望远镜)”项目团队采取了不同的策略:他们观测了在暗淡的矮星前面经过的行星,银河系的这种矮星在数量上要多得多。从2010年开始,该团队利用欧洲南方天文台(ESO)在智利建造的拉西拉天文台,凭借一架0.6米的机器人望远镜,很快发现了这个后来被称为TRAPPIST-1的系统。

 Transit surveys stare at stars, watching for the telltale dip in brightness that occurs when an orbiting planet passes in front and blots out a tiny bit of light. The duration of the dip determines the planet’s orbit, while the depth of the dip determines the planet’s size. Because dwarf stars are so small and dim, transiting planets block a bigger proportion of the light—making the transits more apparent from Earth.

 凌日观测要将镜头对准恒星,观察那种能够说明问题的亮度变暗。做环绕运行的行星在恒星前经过时,会遮挡很少一部分光线,这时恒星亮度就会变暗。变暗的持续时间决定着轨道的长短,而变暗的程度决定着行星的大小。由于矮星很小、很暗,凌日行星就会遮挡较大一部分光线,这样从地球上观测,凌日现象就更加明显了。

 TRAPPIST-1, which is 39 light-years distant and just 8% the mass of the sun, caught the team’s attention because it was obvious from multiple dips that more than one planet orbited the star. Last May, the team published in Nature the discovery of three Earth-sized planets in orbit around it. Finding that many was “an amazing discovery,” Henning says.

 TRAPPIST-1位于39光年之外,只有太阳质量的8%。该系统之所以引起团队的注意,是因为它明显地发生了多重变暗现象,这不仅仅是一颗做环绕运行的行星造成的。去年5月,该团队在《自然》杂志公布了三颗地球大小的行星围绕着TRAPPIST-1运行的相关发现。亨宁说:“发现那么多类地行星,真是令人吃惊!”

 But there were more planets to come. “There was a forest of transits,” Queloz says. “We could not make sense of it.” The team used NASA’s Spitzer Space Telescope along with observations from telescopes on Earth, including ESO’s Very Large Telescope in Chile and others in Morocco, Hawaii, Spain, and South Africa. A final, nearly continuous 20-day observation with Spitzer in September 2016, during which the team saw 34 transits, allowed them to untangle the mess. “Spitzer made all the difference,” team member Emmanu?l Jehin of the University of Liège in Belgium told a press conference yesterday.

 但是,接下来还有更多的行星呢!奎洛兹说:“该系统存在许多凌日现象,我们当时感到无法理解。”该团队利用美国国家航空航天管理局的斯必泽太空望远镜,以及地球表面天文台的望远镜,包括位于智利的ESO甚大望远镜和摩洛哥、夏威夷、西班牙、南非等地的其他望远镜。20169月,最终利用斯必泽望远镜进行了长达20天的连续观测,在此期间该团队观测到34次凌日现象,使他们解开了这个谜团。昨天,比利时列日大学的团队成员伊曼纽尔·耶因在一次记者招待会上称:“斯必泽望远镜就是与众不同!”

 In a paper published today in Nature, the team describes a tightly packed group of planets with orbits ranging from 1.5 to 12.3 days. The dimness of the star means that, despite the planets’ close orbits, all seven could conceivably harbor liquid water on their surfaces. Three are firmly in the “habitable zone,” with enough starshine to have liquid water oceans, as long as they have Earth-like atmospheres.

 今天,在发表于《自然》杂志的一篇论文中,研究团队描述了一组紧凑的行星,公转周期从1.5天至12.3天不等。这颗矮星的变暗情况意味着:尽管这些行星的轨道距离矮星很近,但是所有七颗行星的表面都有可能拥有液态水。其中三颗行星位于“宜居带”上,很稳定,拥有足够的光线,只要拥有类似地球上的大气,就会支持液态水的海洋存在。

 Their orbits are not random but appear to be in a so-called chain of resonance, meaning that the orbital period of each planet is related to that of its neighbors by a ratio of small whole numbers. For example, for every eight orbits made by the innermost planet, the next planet orbits five times, while the next one out orbits three times. Planets don’t form in such tidy arrangements, which suggests that the TRAPPIST-1 planets were born in orbits farther out, before migrating inward and becoming trapped in the stable, resonant orbits. Forming in the system’s colder outer regions, where volatile compounds such as water and carbon dioxide freeze out, makes it possible that the planets incorporated those ices and carried them along to a warmer place where they could melt, evaporate, and become oceans and atmospheres.

 这些行星的轨道并非没有规律,而是好像处于一种所谓的“共振链”中,这意味着每一颗行星的轨道周期都跟相邻行星的轨道周期相关,其比率均为小整数。例如:最内部的行星每公转8圈,与其相邻的行星公转5圈,而下一颗相邻的行星则公转3圈。行星轨道通常不会形成这么整齐的排列,这说明TRAPPIST-1系统中的行星诞生之后,轨道相距较远,当时的行星还没有向内迁移,没有被束缚在稳定的共振轨道中。这些行星在外围较冷的区域形成,像水和二氧化碳等易挥发的化合物冻结,因此这些行星有可能含有这些化合物结成的冰,然后携带着这些冰一路到达较为温暖的区域,最后融化、蒸发,变成海洋和大气。

 One question that hangs over these planets is whether they are rocky, like Earth, or gassy, like mini-Neptunes. A measure of their density would answer that question. But for that, astronomers need to know their mass—individual transit studies reveal only size. However, in the case of TRAPPIST-1 the team was able to estimate masses by watching for a subtle gravitational effect on the planets’ orbits. Because the planets are bunched, they exert a small gravitational pull when they pass by each other. This occasional tug causes some transits to occur slightly later or earlier than expected. By measuring these transit timing variations and performing some fearsome modeling of the system, they were able to estimate the planets’ masses—and work out their densities. They all seemed to be rocky.

 围绕这些行星产生的一个问题就是:它们是像地球一样的岩石行星还是像迷你型海王星一样的气态行星呢?针对密度测量一下,应该能够解决这个问题。为此,天文学家们需要知道这些行星的质量,而研究某颗行星的凌日情况只能说明其大小。不过,就TRAPPIST-1系统而言,该团队能够通过观测对行星轨道所产生的微妙的引力效应来估算行星的质量。由于这些行星是紧凑的,它们互相之间通过时会产生微弱的引力,这种偶尔产生的引力会引起凌日现象的发生比预期要么稍晚一些、要么稍早一些。通过观测凌日现象在时间上的变化,并且对该系统进行某种复杂的模拟,研究团队能够估算出这些行星的质量,进而计算出它们的密度。经计算,这些行星似乎都是岩石行星。

 The next question for astronomers: Do the planets have atmospheres, and—if so—what are they made of? Transits can reveal atmospheres because as a planet passes in front of its star, atmospheric gases can absorb certain frequencies of the light passing through. Such observations are pushing the spectroscopic powers of even the Hubble Space Telescope to its limits. “Hubble is observing [the system], but it’s a little bit on the edge because of the size of the telescope,” Queloz says. So far, the team has confirmed that neither of the two innermost planets has a thick envelope of hydrogen gas, which is what you would expect if they were mini-Neptunes.

 对于天文学家们来说,下一个问题是:这些行星有大气吗?如果有的话,是由什么气体构成的呢?通过凌日现象可以揭示出大气情况,因为当一颗行星在其恒星前经过的时候,大气中的气体可以吸收穿过大气的特定波段的光线。但是,这样的观测甚至将哈勃太空望远镜分光镜的能力都推到了极限。奎洛兹说:“哈勃太空望远镜正在观测这个系统,但是由于该望远镜的大小而受到局限,观测有些靠边。”到目前为止,该团队已经证实,最内部的两颗行星都没有厚厚的一层氢气——如果属于迷你型海王星的话,会含有氢气层的。

 Realistically, any detailed study of TRAPPIST-1’s atmospheres will have to wait for the launch of Hubble’s successor, the James Webb Space Telescope (JWST), due late next year. With the frequent transits, “you can just stare with JWST,” Henning says. He thinks the JWST will be able to tease out the composition of the planets’ atmospheres, which has never yet been achieved for an Earth-sized exoplanet. Discerning biomarkers—which could be a particular mixture of methane, ozone, and oxygen—within those atmospheres, however, will be “extremely challenging,” Henning says. “It’s a goal, but may take longer than the next couple of years.” It may also take the muscle of the next generation of extremely large telescopes on Earth, which will debut next decade.

 实际上,对TRAPPIST-1系统的任何详细研究都必须要等到接替哈勃的望远镜——詹姆斯-韦伯太空望远镜(JWST)的发射升空,该望远镜计划于明年年底发射。亨宁说:“对于这种频繁的凌日现象,你完全可以利用JWST去观测。”他认为,JWST将能够分析出这些行星大气中的气体成分。对于地球大小的系外行星来说,天文学家们从来都没有获得过这样的资料。亨宁称:“在这些行星的大气中,生物标记物可能是一种特定的甲烷、臭氧和氧的混合物,然而辨别这些生物标记物将是极具挑战性的。这是我们的目标,但是要实现这个目标可能并不是接下来几年就能做到的。”此外,要想实现这一目标,可能还需要下一代巨型地面望远镜的力量,这种望远镜将于下一个十年面世。

 Researchers are prepared to wait a few more years for this, perhaps the greatest prize in astronomy. But the discovery of TRAPPIST-1 certainly gives them more hope that they will get there. The TRAPPIST project was only a forerunner for a more concerted search for exoplanets around dwarfs called SPECULOOS, which will rely on four 1-meter telescopes currently being installed at ESO’s Paranal Observatory in Chile. Over the next few years it will survey a thousand such stars. “Imagine how many similar systems may be out there,” Madhusudhan says. “The universe could be teeming with these things."

 为了实现这一目标,研究人员准备再等待几年,或许这将成为天文学史上最伟大的发现。然而,TRAPPIST-1系统的发现肯定会带给研究人员更多的希望,使他们更加相信有朝一日会抵达那里。TRAPPIST项目只是寻找系外行星的前奏,随后还有合作更加广泛的、寻找矮星周围系外行星的项目,该项目被称为“SPECULOOS”,项目的开展将要依靠四架1米的望远镜,目前ESO智利帕拉纳尔天文台正在安装这些望远镜。在接下来的几年中,SPECULOOS项目将要搜寻一千颗这样的恒星。马杜苏丹说:“想象一下类似的系统会有多少吧,宇宙中可能充满了这样的系统!”

   
译自:http://www.sciencemag.org/
原著:Daniel Clery(丹尼尔·克利里)
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