University of Central Florida, PO Box 162385, Orlando, Florida 32816-2385, USA.
Nature. 2010 Apr 29;464(7293):1320-1. doi: 10.1038/nature09029.
It has been suggested that Earth's current supply of water was delivered by asteroids, some time after the collision that produced the Moon (which would have vaporized any of the pre-existing water). So far, no measurements of water ice on asteroids have been made, but its presence has been inferred from the comet-like activity of several small asteroids, including two members of the Themis dynamical family. Here we report infrared spectra of the asteroid 24 Themis which show that ice and organic compounds are not only present on its surface but also prevalent. Infrared spectral differences between it and other asteroids make 24 Themis unique so far, and our identification of ice and organics agrees with independent results that rule out other compounds as possible sources of the observed spectral structure. The widespread presence of surface ice on 24 Themis is somewhat unexpected because of the relatively short lifetime of exposed ice at this distance ( approximately 3.2 au) from the Sun. Nevertheless, there are several plausible sources, such as a subsurface reservoir that brings water to the surface through 'impact gardening' and/or sublimation.
有人认为，地球目前的水资源是由小行星提供的，时间是在产生月球的那次碰撞之后（那次碰撞会将任何先前存在的水蒸发掉）。到目前为止，还没有对小行星上的水冰进行测量，但从包括 Themis 动力家族的两个成员在内的几个小行星的彗星状活动中推断出了其存在。在这里，我们报告了小行星 24 Themis 的红外光谱，表明冰和有机化合物不仅存在于其表面，而且还很普遍。它与其他小行星之间的红外光谱差异使得 24 Themis 迄今为止独一无二，我们对冰和有机物的识别与排除其他化合物作为观察到的光谱结构可能来源的独立结果一致。由于在离太阳约 3.2au 的这个距离处暴露的冰的寿命相对较短，因此 24 Themis 表面冰的广泛存在有些出人意料。然而，有几种合理的来源，例如一个地下水库，它通过“冲击园艺”和/或升华将水带到表面。
