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望远镜和太空任务

望远镜和太空任务

Further proof of extraterrestrial origin of 准晶体s

13 Aug 2012
建立准晶体

An international team of researchers has found nine new samples of naturally occurring 准晶体s. The work also provides further proof that 准晶体s were delivered to the Earth by a meteorite. The team’这项发现挑战了我们对晶体学和太阳系形成的理解。

常规的晶体结构由周期性重复的原子或原子簇构成。这些模式通常限于两倍,三倍,四倍或六倍旋转对称–与360度旋转过程中晶体出现多少次相同的数字°。长期以来,这些规则被认为是一成不变的规则,并且认为不存在破坏这些条件的晶体。

有序但非周期性

然而,以色列物理学家丹尼尔·谢赫特曼(Daniel Shechtman)于1984年发现了这种打破常规的晶体,并因其努力而荣获2011年诺贝尔化学奖。谢克曼发现了一个准晶体–一种有序的晶体,不包含周期性重复的结构。施克特曼’s晶体也具有10倍的旋转对称性。即使在他被发现后,人们仍然对这种材料的存在持怀疑态度。但是随着岁月的流逝,其他物理学家开始构造自己的准晶体,现在已经有100多个 发现了不同的类型。但是,这些是合成的,并且是在精确控制的实验室条件下创建的。就像最初假定准晶体不存在一样,在发现它们之后,也假定准晶体不可能在更广阔的世界中自然存在。

该假设在2009年普林斯顿大学时受到质疑’s Paul Steinhardt –最初创造这个词的人“quasicrystal” – appeared to have discovered a naturally occurring variety in a rock sample from Russia. Steinhardt and his colleague Luca Bindi, from the University of Florence, Italy, measured the ratio of oxygen isotopes within the sample and their results suggested that the rock belongs to a class of meteorites known as carbonaceous chondrites. Not only did this rock contain a naturally occurring 准晶体, it also came from outer space.

激动过去

But the scepticism that had followed 准晶体s around since their discovery continued. The rock sample was traced back to Valery Kryachko, a Russian who in 1979 had been panning for platinum in a stream flowing through the Koryak mountains in far-eastern Siberia. The rock had somehow turned up in Bindi’的意大利博物馆收藏。“人们对岩石持怀疑态度’关于佛罗伦萨的故事涉及秘密日记,走私者和克格勃特工,” Steinhardt told physicsworld.com.

“解决辩论的唯一方法是尝试寻找更多样本,”斯坦哈特解释。他组建了一支由10名科学家,两名驾驶员和一名厨师组成的团队,并展开了为期四天的西伯利亚考察之旅,回到了Kryachko找到原始样本的溪流中。到达那里后,他们摇摄1.5 从河堤中提取出的沉积物,最终分离出几公斤用于分析。

经过六周的细粒度分析,他们发现了一些特别之处。“我们发现了上面有金属斑点的谷物。它不仅包含准晶体,而且氧同位素比值与原始样品完全相同,” says Steinhardt. “那是一个不可思议的时刻。在现场,没有人押注成功找到任何东西的机会超过1%,”他补充说。该小组共分离出九个准晶体样品。据认为这些样品都来自同一陨石,对沉积物层的分析表明,它降落在最后15,000个 years.

极端形成

As the 准晶体s come from a carbonaceous-chondrite meteorite, they must have formed in the earliest days of the solar system. Carbonaceous chondrites are thought to have collided together to form the cores of the rocky planets, and so Steinhardt’s 准晶体s are older than the Earth itself. However, current models cannot account for the presence of these 准晶体s. “我们需要一种新颖的地质过程来形成它们,因此它挑战了我们关于太阳系形成的想法,” Steinhardt says.

太阳系中存在的强烈条件 ’s youth also challenge the prevailing view of 准晶体s as objects that need a carefully controlled laboratory set-up to produce. “准晶体不是以前认为的精细材料。我们发现的那些必须是在早期太阳系的强壮和艰苦条件下形成的,” Steinhardt says.

Others agree that the world of 准晶体s could be changed by this 10-fold increase in the number of known naturally occurring examples. “This result emphasizes how normal 准晶体s are and will hopefully make them less of an eccentricity,”美国宾夕法尼亚州立大学表面物理学研究员雷妮·迪尔(Renee Diehl)告诉 physicsworld.com. “我们看到他们可能已经在我们周围,而我们只是没有注意到,” she explains.

该研究发表在 物理学进展报告.

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