月表温度对于月幔对流影响的数值模拟研究

行星内部对流计算中, 一般都将其表面温度作为常温处理.但在月球、水星等无大气的天体表面, 温度与纬度明显相关, 月球两极和赤道的平均温度相差可以达到100 K以上.纬度相关的温度边界条件, 是否会影响天体早期对流特征与内部热状态, 过去没有得到重视和研究.本文使用有限元方法进行了二维球壳对流模型的热演化模拟, 以评估无大气行星上, 与纬度高度相关的表面温度对其内部对流和演化的影响.模拟计算结果表明, 表面温度会对月球对流形态产生较大影响, 两极因为相对更冷而易于形成下降流, 上升流更倾向于从赤道位置开始, 在早期演化中表现得尤为明显.受边界条件影响, 月球两极与赤道的岩石圈厚度差异可以达到400 km以上.今后在研究太阳系内月球、水星一类没有大气的天体演化、特别是早期演化时, 对于表面温度纬度相关分布的影响应该予以考虑.

Influence of surface temperature on lunar convection

The surface temperature is generally considered to be constant in planetary thermal convection calculations. However, the temperature is significantly correlated with latitude on the surface of non-atmospheric bodies such as the Moon and Mercury. The average temperature difference between the lunar poles and the equator can reach more than 100 K. Whether the latitude-dependent temperature boundary conditions affect the early convective characteristics and internal thermal state of celestial bodies has not been paid much attention and studied in the past. In this paper, thermal evolution simulations of a two-dimensional spherical-shell convection model using the finite element method are performed to assess the effect of the latitude-dependent surface temperature on the internal convection and evolution on an atmosphere-free planet. The results of the simulations show that surface temperature largely affects the lunar convection pattern. The poles are prone to form downwelling plumes because of lower temperatures, and upwelling plumes prefer to start from the equatorial position, particularly evident in the early evolution. The difference in lithospheric thickness between the lunar poles and the equator can exceed 400 km due to boundary conditions. The influence of the latitudinal correlation of surface temperature distribution should be taken into account when studying the evolution of non-atmospheric bodies in the solar system in the future, especially in early evolution.