宇宙是一個很大的化學裝置

MOST people think of the empty space between the stars as being, well, empty. But it is not. It is actually filled with gas. Admittedly, at an average density of 100-1,000 molecules per cubic centimetre (compared with 100 billion billion in air at sea level), it is a pretty thin gas. But space is big, so altogether there is quite a lot of it.

大多數人們認爲星星之間就是空無一物，但事實並非如此。實際上有氣體彌散其中。誠然，分子平均密度10^2-10^3/cm^3的氣體非常稀薄（海平面處是10^26/cm^3）。不過由於空間很廣闊，氣體分子總體數量是可觀的。

Most of it, about 92%, is hydrogen. A further 8% is helium, which is chemically inert. But a tiny fraction—less than one-tenth of a percent—consists of molecules with other elements, such as oxygen, carbon and nitrogen, in them. Though these other elements are a mere soupçon of the interstellar soup, they do give it real flavour.

大部分（約92%）的氣體是氫，另外8%是惰性氣體氦。還有一小部分（不超過千分之一）由氧、碳、氮等其他元素構成的分子。雖然這些元素僅僅是“星際濃湯”輕微的調料，但它們確實增添了湯的味道。

Signs of life

生命的跡象

So far about 180 types of these molecular ingredients have been detected in space from their microwave spectra—the energy produced when molecules rotate around their chemical bonds. There are two reasons for wanting to study them. One is that these molecules are probably the precursors of life. The other is that the rarefied nature of astrochemistry changes the way processes work. It means the individual steps in chemical reactions can be disentangled from one another in a way that is hard—and sometimes impossible—on Earth. And it allows reactions to happen that are unknown on Earth.

到目前爲止，人們已經通過微波譜線探測出約180種分子成分。分子繞其化學鍵旋轉時，分子能級會發生改變，從而產生微波譜線。研究微波譜線有兩個原因。一是分子可能是生命的預兆。二是天體化學其稀薄的屬性會改變化學反應的過程。人們可以用這種方式把化學反應中獨立的一步從彼此步驟間分離出來，有時這在地球上很難實現。並且還有可能發生人類未知的化學反應。

Now the astrochemists have a new tool: the Atacama Large Millimetre/submillimetre Array (ALMA) in northern Chile. It was officially opened on March 13th but has already been making discoveries, including the most intense bursts of star birth in the early universe. ALMA consists of 66 dishes and is the world’s most powerful radio telescope. At a cost of $1.3 billion it should provide a hundredfold increase in sensitivity and resolution over the best older instruments.

現在天體化學家有了新工具：阿塔卡馬大型毫米/亞毫米波天線陣（ALMA，位於智利北部）。3月13日ALMA正式運作，到現在已經有了發現，例如宇宙早期恆星誕生最激烈的爆發。ALMA有66臺天線，是世界上最強勁的射電望遠鏡。花費13億美元想必會使靈敏度分辨率比過去最好的儀器還要好百倍。

Those older telescopes had to focus on nebulae, where the interstellar gas is most concentrated (a familiar one, visible through binoculars, is the gas cloud around the stars that make up Orion’s sword). And older telescopes can detect only strong, simple signals of the sort emitted by small molecules like carbon monoxide and hydrogen cyanide, which have two and three atoms respectively. Spotting more complex substances was almost impossible because their rotational energy is scattered by their numerous bonds across a wide range of frequencies.

以往的望遠鏡必須關注星雲，那裏是星際氣體最集中之處。一個可用雙筒望遠鏡看到的典例是氣體環繞恆星所形成的獵戶座的”劍”。並且老望遠鏡只能探測到一氧化碳（雙原子）、氫氰化物（三原子）等小分子釋放出的強的，簡單的信號。而鑑別更復雜的物質幾乎不可能，大量化學鍵佔有很寬的頻率範圍，以至於旋轉能被散射掉。

ALMA, by contrast, can detect such things routinely. It has already identified glycolaldehyde and acetone, molecules that have eight and ten atoms respectively. In particular, ALMA’s masters, a consortium of research agencies from Canada, Chile, Europe, Japan, Taiwan and the United States, hope to find simple sugars and organic acids—molecules most researchers in the field believe were needed to get life going on Earth.

相反ALMA可以輕易探測到這些信號：它已經鑑定出了乙醇醛（8原子分子）和丙酮（10原子分子）。特別的，由加拿大、智利、歐洲、日本、臺灣及美國的財團組成的研究機構掌控ALMA，希望以此尋覓簡單的糖類和有機酸——該領域大多數研究人員認爲它們是地球上生命的必需之物。

The ability to study chemical reactions stage by stage will be equally important. High-school chemistry lessons, with their neat equations transforming, say, 2H₂ + O₂ into 2H₂O, miss out a plethora of intermediate steps such as (in this case) the formation of hydroxyl, OH. In a lab, these intermediates are often too short-lived to be detectable. But in space an intermediate may hang around a long time before it encounters its partner in the next stage of a reaction. ALMA can see the microwave traces of such intermediates, and thus gain a better understanding of them.

能夠研究化學反應中的每一步同樣很重要。高中化學課上簡單的反應方程式省略了大量的中間步驟。例如2H₂ + O₂ = 2H₂O就沒有體現形成羥基（OH）的過程。實驗室裏，這些中間過程非常短暫，人們難以探測。不過在太空中，一箇中間過程會持續很長時間，直到碰到下一步反應的搭檔。ALMA可以看到這些中間過程的微波軌跡，因此研究者可以更好的瞭解這些過程。

There are also completely new reactions to discover. Anthony Remijan, of America’s National Radio Astronomy Observatory, who is one of the astronomers putting ALMA through its paces, is studying the formation of methyl formate, a compound widely used on Earth in applications from insulation to insecticides. Usually it is synthesised either from methanol and formic acid, or methanol and carbon monoxide. But there is, in theory, a third route that uses formic acid and an unstable substance made from methanol and hydrogen. This has not been seen in an Earthly laboratory, but Dr Remijan thinks it is an important pathway in space, and ALMA should soon tell him if he is right.

還有全新的反應有待人們發現。美國國家射電天文臺的Anthony Remijan是將ALMA引入這個方向的天文學家中的一員。他正在研究甲酸甲酯的形成過程。從絕緣體到殺蟲劑，可以說地球上到處都是甲酸甲酯。通常它由甲醇和甲酸，或甲醇和一氧化碳合成。但是在理論上，還可以使用甲酸和一種不穩定的物質來製造甲酸甲酯。（不穩定的物質則由甲醇和氫來形成。）這還沒有在地球上的實驗室中發現，但Remijan博士認爲在太空中這是一個重要的過程。ALMA應該很快就會告訴他他是否正確。

Probably, that particular discovery will have no practical consequences. The known syntheses are effective, and methyl formate is already cheap. But it will prove a principle about using the cosmos as a chemistry laboratory,and the hope is that similar findings about other molecules that are harder to make may allow chemical engineers at home to reformulate their that happens, the test tube in the sky really will have proved its worth.

也許，上述特別的發現不會產生實用效果。甲酸甲酯熟知的合成方法很有效，而且它很便宜。但是，這證明了一個理念：用宇宙充當化學實驗室。希望有關其他較難製造的分子的類似發現能夠讓化學工程師在家裏重新制定它們的合成過程。如果可以，天空中的試管確實有其價值。