类地行星热物理条件与热演化影响因素分析——以火星地幔热柱演化为例

The study of the inner thermal physical conditions and their effect on the thermal evolution of terrestrial planets:An example for Martian mantle plume evolution

太阳系内类地行星具有相似的岩石层包围金属核的圈层结构,在行星幔的热演化历史起源方面具有同时性和同源性,并且都在早期变形重力位能加热的基础上随放射性热能衰减而冷却。但是,由于半径、密度、粘度以及表层构造属性等物理条件的差异,其热演化历史各具特色。依据基本的热对流和热传导方程,我们计算分析了类地行星热物理条件差异对行星幔热演化历史的影响。计算表明,类地行星热演化的早期,行星幔热对流是主要的散热方式。半径较大的行星表面热流密度大,平均散热量也大。半径较小的行星内部温差小,粘滞系数高,对流能力低,提早进入传导散热状态,且传导散热的岩石层也比大行星厚。不同边界层热物理条件下,类地行星幔热演化历史会分别出现逐渐冷却的平稳式、包含热柱上涌的波动式、行星幔幕次翻转的周期式等特点不同的热演化过程。火星内部曾经存在的地幔热柱构造与火星地幔热动力学演化过程密切相关。我们从火星地幔热动力学演化模型出发,定量计算与地幔热柱构造演化相关的地幔热动力学演化特征,通过三维球壳数值模拟,研究了火星地幔热演化历史上可能存在的热柱活动造成的火星热演化历史的非单调变化,火星地幔对流环结构随时间的演变方式,以及与边界相关的地幔热柱对火星地形的影响。

The terrestrial planets are very similar in structure that consists of lithosphere and iron-rich core. They are simultaneous and homologous in thermal evolution history. Their mantles had been heated by gravity potential energy before very early, and then have been cooling with the attenuation of the radioactive thermal energy. However, their thermal evolution history is in a variety of ways that arise because of the differences of radius, viscosity and surface tectonics. Based on the equations of thermal convection and thermal conductivity, we computed the thermal evolution history of terrestrial planets under difference thermal physical condition. The results show that the mantle convection is the main way for heat elimination in terrestrial planets in their early thermal evolution. Large planet that has higher heat flow would loss more heat energy on its surface. Small planet that has fewer temperature descents and higher viscosity in mantle would have the poor convection ability, and thus began thermal conductive at an earlier epoch. The lithosphere of small planet would be thicker than that of large planet in the conductive situation. With the different physical conditions on upper boundary layer, the planetary would represent dissimilar thermal evolution modes. The differences thermal evolution modes among the terrestrial planets appear in our study are monotonic cooling mode, non- steady-state wave mode and overturn at regular intervals or periodicity mode. Martian mantle plume is closely related to Mars thermal dynamic evolution process. We set off from the Martian mantle thermal dynamic evolution model, and quantitatively calculated the mantle plume thermal dynamic evolution characteristics. Based on three dimensional numerical simulation of the spherical shell, we studied non-monotonic Martian mantle thermal evolution history, and mantle convection ring structure, as well as Martian terrain evolution.