2023年10月25日出版的《自然》杂志发表了法国科学家的一项最新研究成果。来自巴黎城市大学的 Samuel, Henri 的研究团队，提出了火星地核上方富集的熔融硅酸盐层的地球物理证据。

研究团队表明，这种结构与所有地球物理数据兼容，特别是(1)深反射和衍射地幔地震相位，(2)地震频率上的弱剪切衰减和(3)火星在火卫一潮汐上的耗散性质。在这种情况下，地核大小为 1,650±20km，这意味着其密度为 6.5g cm^-3。比以前的地震估计值大 5-8 %，并且可以用比以前所需的合金轻元素更少、更不丰富来解释，其数量符合实验和宇宙化学的限制。最后，研究人员认为层状地幔结构需要外部来源，来产生在火星地壳中的磁信号记录。

据研究人员介绍，火星深层反射 S 波的探测，要求与实验岩石学限制不相容的轻元素含量，从而推断出火星地核的大小为 1,830±40km 。该推断假设火星地幔的成分是均匀的，但这与最近测量到的沿火星地核—地幔边界衍射的传播异常缓慢的 P 波不一致。另一种假设认为火星的地幔是不均匀的，该假设是早期岩浆海洋凝固形成一个富含铁和产热元素的基底层的结果。这种富集导致在地核上方形成熔融硅酸盐层，覆盖有部分熔融层。

附：英文原文

Title: Geophysical evidence for an enriched molten silicate layer above Mars’s core

Author: Samuel, Henri, Drilleau, Mlanie, Rivoldini, Attilio, Xu, Zongbo, Huang, Quancheng, Garcia, Raphal F., Leki, Vedran, Irving, Jessica C. E., Badro, James, Lognonn, Philippe H., Connolly, James A. D., Kawamura, Taichi, Gudkova, Tamara, Banerdt, William B.

Issue&Volume: 2023-10-25

Abstract: The detection of deep reflected S waves on Mars inferred a core size of 1,830±40km, requiring light-element contents that are incompatible with experimental petrological constraints. This estimate assumes a compositionally homogeneous Martian mantle, at odds with recent measurements of anomalously slow propagating P waves diffracted along the core–mantle boundary. An alternative hypothesis is that Mars’s mantle is heterogeneous as a consequence of an early magma ocean that solidified to form a basal layer enriched in iron and heat-producing elements. Such enrichment results in the formation of a molten silicate layer above the core, overlain by a partially molten layer. Here we show that this structure is compatible with all geophysical data, notably (1) deep reflected and diffracted mantle seismic phases, (2) weak shear attenuation at seismic frequency and (3) Mars’s dissipative nature at Phobos tides. The core size in this scenario is 1,650±20km, implying a density of 6.5g cm^-3, 5–8% larger than previous seismic estimates, and can be explained by fewer, and less abundant, alloying light elements than previously required, in amounts compatible with experimental and cosmochemical constraints. Finally, the layered mantle structure requires external sources to generate the magnetic signatures recorded in Mars’s crust.

DOI: 10.1038/s41586-023-06601-8

Source: https://www.nature.com/articles/s41586-023-06601-8