【经济学人】什么？！城市泥浆惊现小陨石？！|2016年12月17日|总第761期

ABOUT 4.6bn years ago,  a spinning disc of gas and dust began to coalesce into balls of matter. The largest sphere , at the disc’s centre, collapsed under its own gravity to form the sun. Other clumps of dust, scattered around its periphery , became planets and asteroids. In planets this dust has long since metamorphosed into rock. But in many asteroids it is still more or less intact . As a consequence, when asteroids collide , some of it is liberated—and a small fraction of that material eventually falls to Earth as micrometeorites. This micrometeoritic dust arrives at a rate of around six tonnes a day. Spread over Earth’s surface, that amounts to just one particle per square metre each year.

大约46亿年前，宇宙中盘旋的气体和尘埃开始混合，形成一个一个的球状物体。其中最大的混合球体受自身重力影响发生爆炸，于是太阳就诞生了。而其他散落在太阳的周围的尘埃团成为了行星和小行星。构成行星的尘埃团早已硬化成岩石，但许多小行星上的尘埃团却或多或少的保留着原始的样子。因此，当小行星发生碰撞时，其中的一些气团就被释放出来，最终一部分跟随小行星以微小陨石的形态落向地球。这些微观陨石灰尘以每天六吨的频率达到地球，但除以地球的总表面积，每平方米覆盖值就如一颗粟米落入沧海，不值一提了。

• Micrometeorite: n 微小陨石

• Gutter：n 贫民窟；排水沟

• Planetary：行星的

• Coalesce：v 联合

• Sphere： n 球体

• Periphery：n 边缘

• Metamorphosed：v 使变质

• Intact：a 原封不动的

• Collide：v 碰撞

Researchers go to great lengths to gather these grains, because they can reveal details of the solar system’s composition and history. They normally collect them by dredging up ooze from the ocean bed, then sifting and filtering it to find a few precious particles, or by melting tonnes of ice from the Antarctic to see what precipitates. Those two locations have the advantage of being isolated and reasonably free of dust from industrial sources. Now, in a study just published in Geology, a group of researchers have identified about 500 micrometeorites from an unlikely source: gutter sediment from the roofs of buildings in two of Europe’s capital cities.

研究人员竭尽全力收集这些陨石，因为它们可以揭示太阳系的组成和历史的细节问题.。研究人员通常从深海海底捞取淤泥，筛选过滤并从中获取有价值的颗粒，或在南极融化成吨的冰查看沉淀物。海底和南极这两个地点的优势在于它们与世隔绝并且完全不受工业灰尘影响。现今，在近期出版的《地质学》的一篇研究中提出，一组研究人员发现了500颗陨石，而它们都来自一个不太可能的地方：欧洲的两座首都城市建筑的屋顶，从排水沟沉淀物中所提取。

• sediment：n 沉淀物
  

• Dredge：v 捞取

• Ooze：n 软泥

Enthusiastic amateur astronomers have claimed to have found cosmic dust in such urban slurry before. Professional scientists, however, tend to be sceptical of such claims, and none has been verified. Jon Larsen, a Norwegian musician, refused to be discouraged. He collected detritus from gutters in his hometown, Oslo, and also from rooftops in several cities that he visited to play jazz or to attend conferences.

热心的业余天文爱好者声称他们之前就在这样的城市泥浆中发现了宇宙尘埃。然而，专业的天文学家却对这种说法持怀疑态度，因为没有一个曾得到证实过。尽管如此，挪威音乐家Jon Larsen却毫不气馁。他在家乡奥斯陆收集碎屑，也在他参观演奏爵士乐或出席会议的城市的屋顶收集淤泥。

• Cosmic:a 宇宙的

• Detritus：n 岩屑

Micrometeorites contain magnetite, a naturally magnetic form of iron oxide, commonly known as lodestone. Mr Larsen’s first step was therefore to pass his slurry, about 300kg of it, past a magnet and keep anything that stuck. He then examined the 30kg or so of debris that resulted under a microscope, to hunt for cosmic dust. Micrometeorites melt as they zip through Earth’s atmosphere at speeds of around 12km a second. The globules then cool into spherical grains, and the minerals of which these are composed take on a distinctive stripy appearance (see picture). An experienced eye, such as Mr Larsen’s, can thus pick them out from other particles, which tend to be jagged and lack these markings. Altogether, he found about 500 of these “spherules”, each around 300-400 microns in diameter (a few times the width of a human hair).

陨石含有磁铁矿，一种自然的磁性铁氧化物的形式，俗称吸铁石。因此，Larsen先生的第一步是将他收集的约300KG泥浆放入磁铁，过滤出被磁铁吸引的磁铁矿。然后在显微镜下观察约30kg的样本，从中寻找宇宙尘埃。微小陨石以每秒12km的速度穿越大气层时会溶解。这些溶解后形成的液体球冷却后形成了球形颗粒，并且这些矿物表面会产生明显的条状细纹（如图）。有经验的人比如Larsen先生，可以将其从其他参差不齐、缺乏标记的粒子中区分出来。总之，他大约发现了500颗“小球”，每颗直径大约300-400微米（人类头发宽度的几倍）。

• Debris：n 碎片

• Globule：n 小球

• Stripy：a 有条纹的

To confirm that the spherules were indeed micrometeorites Mr Larsen needed both expertise and more heavyweight equipment than he had at home. He therefore turned to Matthew Genge of Imperial College, London and his colleagues. They analysed 48 items from Mr Larsen’s Oslo and Paris collections under a scanning electron microscope. They were able to confirm that the composition of these matched that of micrometeorites, which tend to be rich in olivine , a greenish semi-precious gemstone. Most tellingly, Mr Larsen’s samples contained iron and nickel alloys common in micrometeorites, but rare in Earth-bound rocks because these metals oxidise rapidly.

为了确认这些球形颗粒就是微小陨石，Larsen先生需要更专业更重量级的先进设备。他向伦敦帝国学院的Matthew Genge先生及其团队寻求帮助。通过电子显微镜的扫描，他们分析了拉森先生的48个奥斯陆和巴黎的收藏品。他们已经可以确认球形颗粒的成分和微小陨石相匹配，而这些成分在绿色橄榄石中含量十分丰富。（橄榄石只是一种半宝石。在宝石学中，宝石一般分为贵重宝石和半宝石两类。贵重宝石主要有四种，即钻石、红宝石、蓝宝石和祖母绿，而其余的宝石，像水晶、玛瑙、红玉髓等属于半宝石。）更值得一提的是，Larsen先生的样品中包含了铁和镍合金，这在微小陨石中很常见，但在地球上非陨石岩中很罕见，因为这些金属很容易氧化。