类地行星地幔对流的比较研究

After the formation of a terrestrial planet, its thermal evolution can be reagarded as a cooling history of the planet when mantle convection plays a key role during the long geolocial time. Mantle convection dominates many aspects of the terrestrial planet, such as thermal state, rate of heat release, internal structure and tectonics, even the formation and extinction of the planetary magnetic field. Taking the size, composition, internal structure and precise material properties of the terrestrial planets into account, this proposal will use numerical method with large scale parallel computation to simulate the mantle convections for Mercury, Venus, Earth and Mars, investigate the effects of mantle convections in different planets and study the conditions under which mantle convection can be generated in a planet. The relationship between the planet internal structure, physical properties of materials, tectonic movement and mantle convection will also be studied. Based on the facts that Mars lost its magnetic field and no magnetic field is found on Venus (probablly caused by resurfacing), the proposal will implement a comparative study of mantle convections among Venus, Earth and Mars to find the reasons that causes the differences. The study will try to answer the questions why Mars suspended mantle convection, whether it will restart and when. It will also try to explain why there is no intrinsic magnetic field on Venus, even there is no evidence of residual magnetic field found on its surface. Furthermore, this study will provide refernce value for the extraplanet research.

类地行星形成之后的热演化是一部冷却史，而地幔对流加速了行星的冷却过程，决定着行星的热状态，同时地幔对流又是类地行星形成内部分层结构、驱动地质构造运动的决定性因素，甚至还左右着行星磁场的形成和消失。本项目将以水星、金星、地球和火星为对象，采用大规模并行数值模拟方法，综合考虑行星的大小、物质组成、分层结构、力学特性等因素，构建全三维数值模型，模拟不同类地行星中地幔对流的形态、强度和演变，研究产生地幔对流的条件，探讨地幔对流与行星内部结构、物性和构造运动的密切关系。尤其对于大小、质量相近的金地火三大行星，将结合行星磁场的形成和消失以及地质构造运动的活动性，对比研究地幔对流的差异并揭示差异形成的原因，探索火星和金星在演化过程中地幔对流可能发生的中止、重启现象。研究将深入了解类地行星地幔对流、内部结构、地质活动、热能释放和磁场演变的关系，并为系外类地行星研究提供参考。

在我国开启行星际深空探测的背景下，本项目对类地行星的地幔对流情况进行了对比研究，为观测到的行星表面地质地貌多样性与行星内部动力学过程的联系提供了理论解释。我们构建了行星地幔对流的物理和数学模型，通过数值模拟，研究了水星产生地幔对流的条件，结果认为水星地幔厚度如在300～600km+范围内，水星现在极可能存在地幔对流，但对流强度较弱。200km厚度则是限制地幔对流发生的阈值；我们对比研究了类地行星地幔对流差异的主要影响因素，认为影响其地幔对流格局的主要因素是与行星大小密切相关的热演化史，以及由温度（热演化）决定的地幔粘滞性。结合太阳系边缘探测计划，对与行星地幔对流类似的冰卫星冰幔对流进行了预研究，尝试解释冰卫星表面地形、热泉等观测现象。本研究不仅能使我们深入了解行星地幔不同的动力学过程，还将为我国的行星探测活动提供科学目标。

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