Mercury's inner core size and core-crystallization regime
Mercury's inner core size and core-crystallization regime
复制标题
DOI：
10.1016/j.icarus.2014.10.038
复制
发表时间：
2015-03-01
期刊：
影响因子：
3.2
通讯作者：
Rivoldini, Attilio
中科院分区：
文献类型：
--
作者：
Dumberry, Mathieu;Rivoldini, Attilio
基于地球的雷达观测水星的旋转矢量，结合信使号航天器的重力观测，得出了水星的转动惯量和它的硅酸盐外壳在88天内的振动幅度。这两个大地测量约束提供了水星内部结构的信息，包括流体核心的存在，核心-地幔边界的半径以及核心和地幔的体积密度。在这项工作中，我们展示了它们如何进一步提供关于固体内核大小和流体核心结晶机制的信息。如果水星的流体核心是一种Fe-FeS合金，硫浓度在共晶富铁的一侧，那么在1西格玛水平上与大地测量观测相匹配的最大内核是1325 +/- 250 km。我们的结果进一步表明，最适合大地测量观测的结晶情景涉及到流体核心中铁雪的形成，并且这种情景更适合具有贫铁地幔成分的模型。因此，水星的发电机很可能与雪的形成相一致。对于大于650 km的内核，雪的形成延伸到内核边界。如果发电机不能通过雪形成的动力学来维持，或者发电机产生的磁场与观测不相容，那么水星的内核必须小于650公里。(C) 2014爱思唯尔公司版权所有。
Earth-based radar observation of Mercury's rotation vector combined with gravity observation by the MESSENGER spacecraft yield a measure of Mercury's moment of inertia and the amplitude of the 88-day libration of its silicate shell. These two geodetic constraints provide information on Mercury's interior structure, including the presence of a fluid core, the radius of the core-mantle boundary and the bulk densities of the core and mantle. In this work, we show how they further provide information on the size of the solid inner core and on the crystallization regime of the fluid core. If Mercury's fluid core is a Fe-FeS alloy with a sulfur concentration on the Fe-rich side of the eutectic, the largest inner core compatible with geodetic observations at the 1 sigma level is 1325 +/- 250 km. Our results further suggest that the crystallization scenario that best fits the geodetic observations involves the formation of Fe-snow within the fluid core, and that this scenario is preferred for models with an iron-poor mantle composition. Consequently, Mercury's dynamo most likely operates in concert with snow formation. For an inner core larger than similar to 650 km, snow formation extends to the inner core boundary. If a dynamo cannot be maintained by the dynamics of snow formation, or if such dynamo produces a magnetic field incompatible with observation, Mercury's inner core must then be smaller than 650 km. (C) 2014 Elsevier Inc. All rights reserved.