托福听力指导：分类词汇之天文学_小升初复习

托福听力指导：分类词汇之天文学

新托福机经背景大讲堂-月球的南极艾特肯盆地(TPO)

(一)南极-艾特肯盆地(South Pole-Aitken basin).简称为SPAB

月球上最大的环形山，同时也是太阳系内已知最大的，形成了South Pole-Aitken basin(SPAB)。这个环形山位于月球的背面，接近南极的Aitken 盆地，直径约2，500 千米，深12千米。

该盆地层略有升高丰度的铁，钛，和钍等化学元素。

(二)In terms of mineralogy(矿物学), the basin floor is much richer in clinopyroxene and orthopyroxene than the surrounding highlands .Several possibilities exist for this distinctive chemical signature. One is that this composition might simply represent lower crustal materials that are somewhat more rich in iron, titanium and thorium than the upper crust. Another possibility is that this composition reflects the widespread distribution of ponds of iron-rich basalts(玄武岩) , similar to those that make up the lunar maria (月海)Alternatively, the rocks here could contain a component from the lunar mantle if the basin excavated all the way through the crust. The origin of the anomalous composition of this basin is not known with certainty at this time, however, and a sample return mission will most likely be required to settle this debate. Complicating matters is the fact that all three of the above hypotheses could contribute to the anomalous geochemical signature of this giant crater. Furthermore, it is possible that a large portion of the lunar surface in the vicinity of this basin was melted during the impact event, and differentiation of this impact melt sheet could have given rise to additional geochemical anomalies.