经济学人科技||系外行星 / 四六文摘

IN THE DELUGE of planets found beyond the solar system over the past decade, those of system TOI-270 might not seem special. There are three of them, orbiting a star 73 light-years away. This is neither the closest system known, nor does it contain the most Earthlike exoplanet. It has, though, sent a buzz through astronomy.

过去十年里，科学家们在太阳系外发现了大量行星，TOI-270恒星系统的行星似乎并不突出。这个系统中有三颗行星，它们绕着一颗73光年外的恒星运行。它既不是已知的离地球最近的恒星系统，也没有与地球最相似的系外行星。但是，它却在天文学界引起了轰动。

TOI-270 was discovered earlier this year by the Transiting Exoplanet Survey Satellite, TESS, an American instrument launched in 2018.(TOI stands for TESS object of interest.) Its innermost world is a super-Earth, a rocky planet a little bigger than Earth that scurries around its parent star once every three days. Farther out, at orbits of around six and 11 days, are a pair of larger objects known as mini-Neptunes. Having representatives of these two types of planet in a single system is a valuable find. It should help astronomers understand a bit better how different sorts of planet form.

TOI-270是今年早些时候由“凌日系外行星勘测卫星”（TESS）发现的。该卫星系统是由美国在2018年发射升空。（“TOI”意为“TESS的目标对象”）这个系统中最深处的行星是一颗“超级地球”，这颗比地球稍大一点的岩石类行星每3天绕母恒星快速旋转一周。再远一点，有一对更大的行星分别以6天和11天的周期绕恒星运行，它们被称为“迷你海王星”。在同一个恒星系统中能形成这两种具有代表性的行星，这个发现很有价值。它能帮助天文学家更好地了解不同种类的行星是如何形成的。

The proximity of TOI-270 to Earth means that it is within range of instruments such as the Hubble Space Telescope, making detailed follow-up studies possible. These will improve estimates of the planets’ sizes and better calculate their masses—information that will show what they are made of. TOI-270 is thus, in the words of Maximilian Günther, an astronomer at the Massachusetts Institute of Technology (MIT), an “exceptional laboratory” that will help answer some of the biggest questions in the rapidly growing science of exoplanetology. These include: why do planets form in the sizes they do? How does the solar system fit into a wider galactic context? And, is there life beyond Earth?

TOI-270与地球邻近，意味着科学家可以用哈勃太空望远镜等仪器探测到它，这使得详细的后续研究成为可能。这些研究将提高对行星大小的预测和行星质量的计算——这些信息能可以展现行星的构成。因此，用麻省理工学院(MIT)天文学家马克西米兰·冈瑟(Maximilian Gunther)的话来说，TOI-270是一个“特殊的实验室”，可以帮助发展迅速的系外行星学解答一些列重大问题。这些问题包括:行星大小是如何形成?太阳系如何融入更广阔的银河系?以及，地球之外有生命吗?

Dr Günther does, admittedly, have skin in the game. He is the lead author of the study that describes the new star system, published this week in Nature Astronomy. That publication was timed to coincide with a gathering, in Cambridge, Massachusetts, of astronomers, chemists, biologists, geologists and others to discuss the results of TESS’s first year of operation.

冈瑟博士切实参与其中。他以主要作者身份撰写了关于新星系的文章，并于本周发表在《自然·天文》期刊上。文章发布的时间正好在TESS系统运行一周年研讨会召开期间，天文学家、化学家、生物学家、地质学家及其他一些嘉宾汇聚在马塞诸塞州的剑桥，对TESS系统运行一年以来取得的成果进行探讨。

TESS is a pathfinder. It discovers nearby planetary systems so that other instruments may study them. It locates its quarry by looking for characteristic dips in a target star’s light caused by planets passing in front of that star. So far, it has found 24 planets the existence of which has been confirmed by other means, and a further 1,000 possibles that are waiting to be checked. It is expected to find thousands more, perhaps tens of thousands, over the course of its four-year mission.

TESS是探路者，它的任务是找出邻近的星系，然后由其他设备对这些星系进行研究。当别的行星从目标星球前方经过时，目标星球的光线会出现凹陷，TESS据此来定位这些行星。截止目前，TESS已经发现了24颗行星，并通过其它方式确认了这些行星的存在，另外还有1000多颗行星有待确认。据预计，在TESS四年的任务期内，它还会发现数千甚至上万颗行星。

As astronomers have catalogued planets found by TESS and other instruments, they have spotted both patterns and puzzles. There are, for instance, lots of super-Earths and lots of mini-Neptunes. But there is a gap between them. Few planets are known that have between one-and-a-half times and twice the diameter of Earth.

在天文学家对TESS及其他设备发现的行星进行分类的过程中。他们发现了一些规律，也遇到了很多问题。比如，他们发现了许多超级地球和迷你海王星。但是两者之间的跨度巨大。目前已知的行星中，很少有直径为地球1.5-2倍的行星。

This so-called “Fulton gap”—named after Benjamin Fulton, a PhD student who noticed it in 2017—could have several explanations. Possibly, planets on either side of the gap are different sorts of object. Super-Earths might be born from dust and rocks, and be kept small by a lack of suitable material from which to grow, while mini-Neptunes, constructed of commoner materials such as ice, can grow much larger. Alternatively, all planets may form in the same way, as mini-Neptunes with rocky Earthlike cores surrounded by thick atmospheres of hydrogen and helium. Some, though, may subsequently have most of their atmospheres blown away by the radiation from their parent star, a process known as photoevaporation.

这就是 “富尔顿分隔带”，在2017年由一位名叫本杰明·富尔顿的博士生发现，并以她的名字命名。对于这种现象有几种解释。一种可行性是位于分隔带两头的行星由不同的物质组成。超级地球由尘灰和岩石组成，由于缺少合适的物质，无法长大；而迷你海王星则是由于例如冰等更为常见的物质组成，因此可以长得更大一些。无论属于哪一种，所有的行星都可以由同样的方式构成，像迷你海王星那样具有地球般的岩石内核，外部由氢气和氦气构成的厚实的大气层包裹。尽管之后有些行星的大气层会遭到母星辐射的破坏，这个过程叫做“光蒸发”。

In the view of James Owen, an astrophysicist at Imperial College, London, TOI-270 presents a way to test the photoevaporation hypothesis. Comparing planets orbiting different stars is hard, because it is impossible to know how much high-energy radiation they have received in the past from their stellar parents. But all three objects in TOI-270 have had the same history in this regard, so Dr Owen has been able to remove that uncertainty and predict what the minimum masses for the outer planets should now be, if the photoevaporation hypothesis is indeed correct. If all TOI-270’s planets started as mini-Neptunes, he says, the two outermost should now weigh at least 1.8 and 1.3 Earth masses respectively. Planned measurements should soon tell him if he is correct.

在伦敦帝国理工学院天体物理学家詹姆斯·欧文（James Owen）看来，TOI-270恒星系统可以用于验证“光蒸发”假说。比较围绕不同恒星轨道运行的行星是很困难的，因为我们不可能知道它们过去在母恒星那里获取了多少的高能辐射。就这点而言，TOI-270恒星系统种的三个行星有着相同的辐射吸收史，所以欧文博士可以排除这种不确定性的影响，在假设光蒸发理论正确的基础上，预测当前外行星的最小质量。他说，如果所有TOI-270恒星系统的行星都始于迷你海王星，那么当前两个最外层行星重量应该分别为1.8个地球质量和1.3个地球质量。计划好的测量结果应该很快会告诉他这一假说是否正确。

注：
A fashion for flares 耀斑的时尚（flares也有喇叭裤的意思，请读者配合笑一笑）

Most of the systems that TESS will catalogue are expected to be orbiting small, red stars known as M-dwarfs. Courtney Dressing, of the University of California, Berkeley, says that planets around these stars could be excellent places for life to develop because M-dwarfs are extremely long-lived and are stable once they reach maturity. They do, however, reach that maturity only after a stroppy adolescence involving intense bouts of activity, regular flares and the release of huge amounts of energy and charged particles.

人们预计将来TESS编录的大多数恒星系统都是围绕着红色小恒星运行的，这种红色小恒星也被称作“M矮星”。加州大学伯克利分校的教授考特妮·德雷辛（Courtney Dressing）说围绕着这些恒星的行星可能是支持生命发展的好地方，因为M矮星的寿命非常长，进入成熟期后就会保持稳定。当然，要进入成熟期必然要经历暴躁的青春期，而在青春期内会有强烈的间断性活动，包括一般性的耀斑燃烧以及释放大量的能量和带电粒子。

All this radiation would be bad for any life that had already developed on a nearby planet, but might, paradoxically, encourage life to emerge in the first place. Some think that ultraviolet light falling on the early Earth provided the energy needed to make the complex organic molecules that were life’s precursors. Mature M-dwarfs do not produce enough ultraviolet for this to happen. But adolescent ones might.

所有的这些辐射对于已经存在于邻近行星的生命是有害的，然而这些辐射也反而可能会激发新的生命。有人认为，照射在早期地球表面的紫外线提供了形成复杂有机物所需要的能量，而这些有机物就是生命的前兆。成熟的红矮星没有足够的紫外线来支持这个过程。但是处在青春期的红矮星也许可以。

Back at MIT, Dr Günther has spotted hundreds of flares on M-dwarfs being scrutinised by TESS—some of which made the stars temporarily 30 times brighter than normal. These data, along with measurements from other observatories, provide details of flares’ probable impacts on exoplanetary atmospheres and will allow Drs Günther and Dressing to test their theories.

而在麻省理工学院后，冈瑟博士在由TESS系统检测到的M矮星上发现了数百个耀斑-其中一些耀斑使这些恒星的亮度暂时比正常亮度高出30倍。这些数据以及来自其他天文台的测量数据呈现了耀斑可能对系外行星大气层产生的影响的详细情况，同时也使得冈瑟博士和德雷辛博士能够顺利测试他们的理论。

TESS will also provide a catalogue of interesting targets, likeTOI-270, for study by future missions. One of these, CHEOPS(Characterising Exoplanet Satellite), will be launched this autumn by the European Space Agency, ESA, with the aim of measuring the precise sizes of as many super-Earths and mini-Neptunes as possible. These data, combined with knowledge of objects’ masses, will lead to a better understanding of what particular planets are made of. Gassy planets will have low densities. “Water worlds” will have rather higher ones. Higher still will be the densities of rocky worlds made principally of silicates. The highest of the lot will belong to those planets made mainly of iron.

TESS还发现了很多有意思的值得研究的星系，可以作为未来的研究目标，例如TOI-270。今年秋天，欧洲航天局将发射一颗名为CHEOPS(系外行星卫星)的卫星目标是准确测量尽可能多的超级地球和迷你海王星的体积。这些数据再加上对物体质量的了解，将有助于人们更好地了解某种特定行星的构成。气态行星的密度较低，“水态”行星的密度要高一些。“岩态”行星主要由硅酸盐构成，其密度更高一些。而密度最高的行星是那些主要由铁构成的行星。

After CHEOPS, ESA’s next planet hunter will be PLATO, a bigger version of TEAfter CHEOPS, ESA’s next planet hunter will be PLATO, a bigger version of TESS—so big, indeed, that it will be sensitive enough to look for terrestrial bodies that, like Earth itself, orbit at longer periods around bright sun-like stars. Oliver Shorttle of Cambridge University reckons that, using PLATO and its successors, astronomers are likely, within three or four decades, to have found all the planets in the nearest portion of the galaxy to Earth. And this will allow the $64,000 question to be answered: how propitious are astronomical circumstances for the development of life?

继CHEOPS(系外行星卫星)之后，ESA(欧洲航天中心)的下一个行星猎手将是PLATO，是一个更强大的TESS系统。– PLATO系统非常强大，灵敏度足以寻找到以更长周期围绕类日恒星运行的类地行星。剑桥大学的Oliver Shorttle估计通过使用PLATO以及之后的探测卫星，在三，四十年内，天文学家很可能发现银河系中近地球区域所有的行星。这样就可以回答这个价值64,000美元的问题：天文环境到底对生命的发展有什么好处？

With an extensive sample of this sort it should be possible to estimate how many Earthlike worlds exist in the galaxy, and what fraction of those are located at a distance from their parent star that might permit liquid water to form on their surfaces. Meanwhile, astronomers and geologists will be scrutinising those examples that have turned up within the range of the telescopes then available, in a bid to understand how their climates work, look for chemical signatures of life, and watch for weather and geological events such as volcanic eruptions. “If we find these alien Edens,” says Dr Shorttle, “how could we not stop and stare?”

有了这些广泛的样本，人们就可以估计星系中有多少类地系统存在，以及它们中的哪些距其母星距离使得液态水能够在其表面形成。同时，天文学家和地质学家还将仔细研究那些能够用更先进的望远镜观测到的的样本，以便了解那里的气候运作，寻找生命的化学特征，并观察天气和地质性事件，如火山喷发等等。Shorttle博士说：“一旦找到了这些外星人的伊甸园，我们怎么可能不停下来仔细观赏一番呢？”

翻译组：

Cindy，女，未来外贸工，TE粉

Yifei，女，英专硕士，专八，二笔

Sinyar，女，理性乐观派，TE爱好者

Angela，女，人大附中，托福110，爱哲学爱猫爱旅行

校对组：

Lee ，爱骑行的妇女之友，Timberland粉

Rachel Zhang，学理工科，爱跳芭蕾，热爱文艺的非典型翻译

观点|评论|思考

本次观点由Pippy独立完成

Piggy，爱吃鱼，爱跳舞，爱睡回笼觉的小能猫，NUS食品系

Gazing into the night sky and the infinite number of stars, the question might just appear naturally: is there anyone out there? Are we alone in the universe?

Many scientists would now argue that the detection of extraterrestrial life is more a question of when, not if. The confidence mainly comes from the speed of scientific advancement and the rate at which exoplanets (planets orbiting other stars) were being discovered in the past 50 years. In 2000, astronomers knew about 50 exoplanets. To date, about 3,800 exoplanets have been confirmed, and 47 of which are regarded as “potentially habitable”.

The more we are able to peer into space, the more it seems plausible that life could be distributed throughout the universe.

Suppose we wake up one morning to learn that extraterrestrial life has been discovered, how would you react? In scientific fiction, often the discovery of alien life is portrayed as having negative consequences – buildings crumble, fires rage, riots break out, and societies collapse. But how true is that? If that’s how Earthlings are going to deal with the news that there is life beyond on Earth, why risk looking for it?

Some scientists remain optimistic. A team led by Michael Varnum from the Arizona State University, who has recently presented their study at the American Association for the Advancement of Science annual meeting, said that people’s survey responses were generally positive towards the scenarios of finding of alien life, which range from hypothetical questions to the famously false announcement of microbial fossils from Mars in 1996. Varnum and his team thus suggested that the public’s reactions to intelligent aliens are likely to be similarly positive.

But not everyone agrees that the study’s results can be generalized. There are light-years of difference between acknowledging the presence of harmless (and long dead) microbes on the next planet and being informed of other civilizations whirling around out there in the universe.

To date, there seems to have no solid evidence to rebut our beliefs that human beings are the winners of natural selection, and occupy a privileged position in relation to other creatures. However, with the discovery of other alien civilizations, we might find that we are just insignificant creatures living on a tiny planet in a galaxy hiding at the forgotten corner of the universe, in which there are far more galaxies than people. Would the discovery make us feel inferior, and as a consequence, cause people to question their faith and very own existence? How unique are we? We would need to consider whether we could accommodate these new findings, or if our beliefs would be shaken to the core.

Fortunate (or unfortunate) enough, no discovery of alien life has been made. Scientists from the SETI (The Search for Extraterrestrial Intelligence) Institute are still trying to determine whether advanced civilization is part of the cosmic landscape – sending out radio signals and waiting for response, if any, from the mysterious universe.

It is exciting to see how science can bring our understanding about the universe to the next level in the coming years. Till then, we still have plenty of time to consider the potential ethical issues associated with human-alien contact, and possibly come out with an SOP for the event.

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