应用重力场模型二阶位系数及新近岁差率约束火星内核大小及密度组成  

Constraining the size and density composition of the Martian core by using second-order potential coefficient and recent precession rate of gravity field model

作　　者：钟振[1] 文麒麟 梁金福 Zhong Zhen;Wen Qi-Lin;Liang Jin-Fu(School of Physics and Electronic Science,Guizhou Normal University,Guiyang 550025,China)

机构地区：[1]贵州师范大学物理与电子科学学院,贵阳550025

出　　处：《物理学报》2023年第2期380-386,共7页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:41864001,42030110)资助的课题.

摘　　要：针对当前InSight数据无法检测火星固态内核是否存在的问题,提出利用火星平均密度和平均惯性矩因子估算火星固态内核的大小及其密度组成.根据火星高阶重力场模型JGMRO120f和GMM3-120以及最新火星岁差率,推导了观测数据下的火星平均密度和平均惯性矩因子;参考火星内部结构的4层模型以及不同自由参数(壳层密度、幔层密度、外核密度、内核大小和内核密度),求解了火星平均密度和平均惯性矩因子的模型值.利用观测值与模型值最小残差平方和作为约束条件,大批量统计结果表明:1)两个重力场模型求解的自由参数具有相同的分布特征,自由参数的最优值基本一致;2)火星壳层密度、幔层密度和外核密度接近其他研究结果,表明统计结果有一定的参考价值;3)火星可能存在840 km左右的固态内核,其密度约为6950 kg·m^(-3).内核密度大小表明火星内核不由纯铁物质组成,该结果与火星核富集轻元素物质的近期研究一致,计算结果具有一定的参考价值.由于反演结果的非唯一性,未来随着InSight火星星震数据处理技术的提高,有望进一步约束火星内核的大小及其组成.It is still difficult to detect the existence of Martian solid inner core merely based on Mars seismic InSight data.To deal with this problem,our study intends to use the mean density and mean moment of inertia factor to constrain the size and density of Martian solid inner core.Using the Mars high-degree gravity field models:JGMRO120f and GMM3-120,and considering the recent precession rate,we obtain the mean density and mean moment of inertia factor,which are treated as the observed values.Referring to the 4-layers internal structure model of Mars,and considering the 4 parameters,i.e.crustal density,mantle density,density of outer core,size and density of inner core,we calculate the modeled values of the Martian mean density and the mean moment of inertia factor.From the minimum residuals between observed and modeled values of mean density as well as that of mean moment of inertia factor,it is found that the two gravity field models have the same result of distribution of free parameters.As to the optimized values of the free parameters,the two gravity field models even have the same results.Furthermore,the optimized crustal density,mantel density and density of outer core approach other studies,indicating the dependence of our results.Finally,our result demonstrates that Mars likely has a solid inner core with a size close to 840 km,and the density of inner core is nearly 6950 kg·m^(-3).Our result implies that Mars has an inner core not fully composed of pure iron,which is consistent with the recent study that Mars requires a substantial complement of light elements in Martian core.However,it is further needed to constrain the size and composition of Martian inner core due to the non-uniqueness of inversion results.With the improvement of processing technology on the InSight data,it can be further constrained for the size and composition of Martian inner core.

关 键 词：InSight 岁差变化率 平均惯性矩因子 火星内核大小 火星内核密度 

分 类 号：P185.3[天文地球—天文学]