太空，这个人类亘古以来奇的地方，也是雅思/托福考试常常涉足的话题，寻找像地球一样的行星是科学家们最执着的追求。新的检测方法有可能让我们离梦想更进一步其中奥妙，大家自行阅读发现一下吧！

Astronomy：Hello, neighbours

The search forexoplanets moves to Earth’s back yard.

摘自The Economist April 21st 2018

Before 1992 astronomers could only presume that alien planets existed.That was the year the discovery of the first such worlds, orbiting a pulsar calledPSR 1257+12, about 2,300 light-years from Earth, was announced. These days,astronomers have more exoplanets than they know what to do with. The ExtrasolarPlanets Encyclopaedia lists 3,767 confirmed worlds as of April 18th, withthousands more detections awaiting confirmation.

This torrent of discovery has made exoplanetology one of the most exciting fields inastronomy. But it is also frustrating, for the majority of those planets are sofar away that, besides the fact of their existence, little can be learned aboutthem. Data on most are limited to the orbits they trace around their parent stars and estimates oftheir sizes and masses.

That is about to change. On April 18th a space telescope called theTransiting Exoplanet Survey Satellite (TESS), blasted into orbit from Cape Canaveral in Florida.TESS is designed to examine almost the entire sky, looking for evidence ofplanets around the nearest (and thus brightest stars)— those, in other words,that are easiest to study in more detail.

Over the course of its two-year mission, TESS will stare at around200,000 of the stars closest to Earth, watching for telltale dips in brightness caused by aplanet crossing in front of its star. The transit method, as this is known, relies on the orbital plane of a planetbeing aligned with the instrument doing the observing, so only a small fraction of any planets orbiting the starsin question will be detectable. Nevertheless, assuming Earth’s cosmic neighbourhood is similar to the galactic average, TESS should turn up around 3,000 planets.

The idea is to provide a target list of the most interesting worlds forfollow-up observations by other instruments using other methods. One suchmethod (the one by which PSR 1257+12’s planets were detected) is to measure the wobble that theplanet’s gravity causes in its parent star as it orbits. Such measurementsreveal a planet’s mass. Since TESS’s transit method reveals a planet’s size,the two together give enough information to calculate its density, and therefore to deduce whether it is made of rock or gas. Several telescopes around the world arebeing upgraded with just such TESS-assisted observations in mind.

Based on existing data, around 500 of the 3,000 planets that TESS isexpected to find are likely to be rocky worlds with radii up to twice that ofEarth. Of those, a couple of dozen might orbit in the habitable zone of their parent stars, wheretemperatures are right for liquid water to exist on their surfaces.

Since liquid water is required by all forms of terrestrial life, looking for it in the cosmosmakes a goodstarting-point in the quest for life of the non-terrestrial sort. And becauseTESS’s planets will be so close to Earth, it should be possible to checkwhether they do in fact possess water, not merely whether they might.

A new generation of instruments, including ultra-large ground-basedtelescopes and the delayed, over-budget James Webb Space Telescope, scheduledto launch in 2020,will be able to observe starlight that has passed through an alien planet’satmosphere on its way to Earth, and from that infer the chemical composition of the exoplanet’sair. The presence of certain gases would be tantalising hints that the planets in questionmightplay host to life. The simultaneous presence of methane and oxygen, for example, would excite interest becausethese two gases react together quickly, and would thus need constant renewal to coexist.

It may eventually be possible, for the closest worlds, to takephotographs of the planets. That could show general details of geography, suchas how much of the surface of a rocky body is covered by liquid and how much byland. Going, in the space of less than 30 years, from knowing nothing at allabout alien planets to making rough maps of them would bea feat of extraordinaryproportions.

重点词汇和表达

orbit v.绕轨道运行

detection n.探测，侦查

a torrent of 一连串的

[torrent n.奔流

trace v.追踪

blast (into) v.迸溅出

telltale n.迹象

transit n.经过，通过

orbital plane 轨道平面

be aligned with 与…一致

a small fraction of 一小部分

galactic adj.银河的，星系的

wobble n.摇晃，不稳定

deduce v.推论，推断

habitable adj.可居住的

terrestrial adj.地球的

cosmos n.宇宙

launch v.发射

infer v.推断

tantalising adj.引起好奇心的

play host to 迎接

simultaneous adj.同时发生的

a feat ofextraordinary proportions 非比寻常的壮举

本文作者简介：

王少娟

上海新航道雅思主讲，上海外国语大学教育技术学硕士。对综合英语的阅读教学有深入的研究，教授了数百名学生均取得了优异的英语成绩。讲解细致、逻辑清晰、课堂活跃，丰富的教学经验能帮助学生在学习中和练习中能够更有效的提高英语能力。

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