□ 曹 燕

雙語小知識（五）

□ 曹 燕

Exoplanets 系外行星（一）

It feels like every time astronomers even look at a star these days, they find a planet or two in orbit around it. They’ve confirmed about 3500 planets in all, with thousands more awaiting confirmation. The planets range from about the mass of the Moon to many times the mass of Jupiter, the largest planet in the solar system. Some are quite close to their parent stars, while others are far away. And some orbit a single star, while others have two suns in their sky — or even three.

近來，好像只要天文學(xué)家們朝一顆恒星看上一眼，就能在其軌道上發(fā)現(xiàn)一兩顆行星。他們已經(jīng)確認(rèn)了總共大約3500顆行星，還有數(shù)千顆正等待確認(rèn)。行星的質(zhì)量范圍從月亮那么大到數(shù)倍于太陽系最大的行星——木星的質(zhì)量。有些離它們的恒星很近，有些卻離得很遠(yuǎn)。有些繞唯一的恒星運(yùn)行，而另外一些則有兩顆甚至三顆太陽高懸于天空。

One amazing thing about these discoveries is that, in an era of giant telescopes, most of the exoplanets were found with small telescopes.

關(guān)于這些發(fā)現(xiàn)，一件令人驚異的事情是：在這個(gè)巨型望遠(yuǎn)鏡的時(shí)代，絕大多數(shù)的系外行星都是用小望遠(yuǎn)鏡找到的。

Most of the planets were discovered with Kepler Space Telescope. The spacecraft looks for a small dip in a star’s light caused by a planet passing across its disk. And it does so with a main mirror that measures just three feet across — quite small by modern research standards.

大部分系外行星是由開普勒太空望遠(yuǎn)鏡發(fā)現(xiàn)的。該航天器尋找行星經(jīng)過恒星圓面時(shí)少許變暗的星光。而它是依靠一個(gè)口徑只有三英尺的主鏡完成這些的——用現(xiàn)代研究的標(biāo)準(zhǔn)看，三英尺口徑確實(shí)非常小了。

圖中所示的是12顆處于宜居帶中的系外行星，它們都有適宜液態(tài)水存在的溫度，這是生命存在的重要條件之一。圖片來源：行星宜居性實(shí)驗(yàn)室（Planetary Habitability Laboratory）

Many ground-based planet searches are done with even smaller telescopes, which devote all their time to hunting planets. A robotic network known as HAT, for example, has discovered almost 60 planets with telescopes that consist of 200-millimeter camera lenses. And a telescope known as KELT-North, which uses an 80-millimeter lens, has discovered four confirmed planets.

很多基于地面的行星研究甚至是通過更小的、專門狩獵行星的望遠(yuǎn)鏡完成的。比如，一個(gè)被稱為HAT的自動監(jiān)測網(wǎng)已經(jīng)發(fā)現(xiàn)了大約60顆行星，監(jiān)測網(wǎng)由多架口徑20厘米望遠(yuǎn)鏡組成。一架被稱為KELT-North的望遠(yuǎn)鏡，運(yùn)用8厘米的鏡片發(fā)現(xiàn)了4顆已被確定的行星。

These little telescopes are helping make some big discoveries about worlds in other star systems.

這些小望遠(yuǎn)鏡正在幫助發(fā)現(xiàn)其他恒星系統(tǒng)中的世界做出大貢獻(xiàn)。

ExoplanetsⅡ 系外行星（二）

The giant planets Jupiter and Saturn are unlikely homes for life. They don’t have solid surfaces, and conditions in their atmospheres aren’t good for the kind of life we have here on Earth. Yet both planets have moons that are considered much more likely abodes for life. The moons have liquid water below their icy crusts, along with sources of energy and the right chemistry for life. That’s inspired astronomers to look for moons orbiting planets in other star systems.

巨行星木星和土星并不適宜成為生命的家園，它們沒有固態(tài)表面，大氣層的條件也不適合類似我們地球上的生物。但是這兩顆行星都有被認(rèn)為好像更加適合生物駐扎的衛(wèi)星。這些衛(wèi)星冰冷的外殼下都存在液態(tài)水，同時(shí)有能源和適合生命的化學(xué)成分。這激勵了天文學(xué)家們尋找其他恒星系統(tǒng)中圍繞行星運(yùn)行的衛(wèi)星。

ExoplanetsⅢ 系外行星（三）

Like most people, many scientists believe there’s some type of life on other planets. It could be as simple as microbes, or as complex as the plant and animal life here on Earth.

和多數(shù)人一樣，很多科學(xué)家也相信其他行星上會存在一些種類的生命。它們可能像細(xì)菌一樣簡單，也可能像我們地球上的植物和動物一樣復(fù)雜。

But there’s a huge gap between believing that something’s there and actually proving it. And so far, there’s no confirmed evidence of life on any world other than our own. Yet astronomers are already trying to tease out that evidence on exoplanets — worlds that orbit stars other than the Sun.

但是相信它們存在和實(shí)際證明它們存在之間有著巨大的鴻溝。到目前為止，除了我們的世界，其他任何地方都沒有生命存在的有力依據(jù)。然而天文學(xué)家們已經(jīng)試圖去梳理在系外行星，太陽以外其他恒星的行星上存在生命的證據(jù)了。

They’re doing so by taking advantage of the fact that most of the worlds discovered so far pass in front of their stars. Astronomers take a spectrum of the star when no planet is in front of it, revealing the star’s chemistry. Then they take another spectrum when the planet passes in front of the star. If the planet has an atmosphere, then some of the star’s light passes through it. Comparing the spectra can reveal the chemistry of that atmosphere.

他們利用這一事實(shí)來進(jìn)行梳理：到目前為止發(fā)現(xiàn)的絕大多數(shù)行星都從它們的恒星前經(jīng)過。天文學(xué)家們拍攝沒有行星經(jīng)過時(shí)恒星的光譜，了解恒星的化學(xué)成分；之后，他們再拍攝有行星經(jīng)過時(shí)的恒星光譜。如果有大氣層，那么一些星光會穿過大氣層。對比兩個(gè)光譜可以發(fā)現(xiàn)行星大氣的化學(xué)物質(zhì)。

右面這幅美術(shù)作品中Gliese 1214b正從其恒星前經(jīng)過。Gliese 1214b也被稱為GJ 1214b，曾經(jīng)被看成是“超級地球”，它比地球大，大概有海王星那么大。整個(gè)Gliese 1214是迄今為止發(fā)現(xiàn)的離太陽最近的恒星系統(tǒng)，約在42光年之外。圖片來源：歐洲南方天文臺（ESO）

Life on Earth produces elements and compounds that are rarely found without life, such as oxygen and methane. So if one of these “biomarkers” turns up in a planet’s atmosphere, it increases the odds that something is living there. And if more than one biomarker is found, especially at high concentrations, then it’s a good bet that it’s a living world.

地球上的生命制造了沒有生命的世界里很難找到的元素和化合物，比如氧氣和甲烷。如果有一個(gè)這種“生命指標(biāo)”出現(xiàn)在行星的大氣層中，這就增加了有生命在那里存在的可能性。如果發(fā)現(xiàn)超過一項(xiàng)的指標(biāo)，尤其是高濃度的，就可以贏率很高地打賭說這是一個(gè)有生命存在的世界了。

Astronomers have used this technique to study the atmospheres of several planets. So far, though, they haven’t found any biomarkers — the signature of life on another world.

天文學(xué)家們通過這一方法研究了幾顆行星的大氣層。但是，到目前為止，他們都沒有發(fā)現(xiàn)任何指標(biāo)，那些在另一個(gè)世界存在生命的信號。

They’ve already discovered several giant planets that are in the habitable zone — the distance from the star where temperatures are just right for liquid water. The planets are too much like Jupiter and Saturn for Earth-like life. But if they have big moons, those worlds could be good abodes for life— small, rocky worlds with lots of water.

他們已經(jīng)在宜居帶（與恒星距離合適，其溫度適宜液態(tài)水存在）發(fā)現(xiàn)了數(shù)顆巨行星。對于類地生命來說，這些行星太像木星和土星了。但是，如果它們有大型衛(wèi)星，那里可能很適宜生命居住——小而且擁有很多水的巖石世界。

Recent simulations by researchers at McMasters University found that such“exomoons” could grow to about twice the mass of Mars — bigger than any moon in the solar system. Such a heavy world could hold on to its water and atmosphere for billions of years— providing plenty of time for life to develop.

最近，麥克馬斯特大學(xué)的研究人員通過模擬發(fā)現(xiàn)，這類“系外衛(wèi)星”可能達(dá)到大約火星質(zhì)量的2倍，比太陽系里所有的衛(wèi)星都要大。如此重大的世界可以在數(shù)十億年中牢牢吸引水和大氣層，為生命的進(jìn)化提供足夠的時(shí)間。

So far, no one has seen any exomoons. They’re quite hard to detect with current technology. But new telescopes on the ground and in space should have the ability to pluck them from the observations of exoplanets — perhaps revealing some distant homes for life.

到目前為止，沒有人見過任何系外衛(wèi)星。以今天的科技來探測它們確實(shí)太難了。但是，地面上和太空中的新型望遠(yuǎn)鏡可能擁有通過觀察系外行星捕獲它們的能力，這也許會揭示一些遙遠(yuǎn)的生命居所。

特別說明：以上三篇文稿英文撰稿均為Damond Benningfield。文章來源于Star Date網(wǎng)站（https://stardate.org/），歡迎大家關(guān)注網(wǎng)站查看原文。

（責(zé)任編輯 張長喜）