Remanent magnetization and active magnetic fields have been detected for several telluric planetary bodies in the solar system (Earth, Mercury, Moon, Mars) suggesting the presence of core dynamos active at the early stages of the planet formation and variable lifetimes. Among the factors controlling the possibility of core dynamos generation, the dynamics of the surrounding silicate mantle and its associated thermal properties are crucial. The mantle governs the heat evacuation from the core and as a consequence the likeliness of an early thermally driven dynamo. In the case of planets with a thick mantle (associated with supercritical Rayleigh numbers), the core heat is efficiently removed by mantle convection and early thermally-driven dynamos are likely. At the opposite, planets with a thin mantle (associated with subcritical Rayleigh numbers) might evacuate their inner heat by diffusion only, making early thermally-driven dynamos difficult. Within the Solar System, Mercury is a potential example of such a regime. Its small mantle thickness over the planet radius ratio might be inherent to its small orbital semi-axis and hence, might be ubiquitous among the terrestrial objects formed close to their star.

To constrain the likeliness of a thermally driven dynamo on “Mercury-like” planets (i.e. with large Rc/R), we present new thermal diffusivity measurements of various solid, glassy and molten samples. We applied the Angstrom method on cylindrical samples during multi-anvil apparatus experiments at pressures of 2 GPa and temperatures up to 1700 K. Thermal diffusivities and conductivities were estimated for solid and partially molten peridotites, with various melt fractions, and for basaltic and rhyolitic glasses and melts. Our study demonstrates that melts have similar thermal properties despite a broad range of composition investigated. The melts reveal much lower thermal conductivities than the solids with almost an order of magnitude of decrease: 1.70 (±0.19) to 2.29 (±0.26) W/m/K against 0.18 (±0.01) to 0.41 (±0.03) W/m/K for peridotites at high temperatures and various melts respectively. Partially molten samples lie in between and several predictive laws are proposed as a function of the melt fraction and solid/melt texture.

Using our results into forward calculations of heat fluxes for dynamo generation for Mercury-like planets, we quantify the effect of mantle melting on the occurrence of thermally driven dynamos. The presence of a mushy mantle and partial melting could significantly reduce the ability of the mantle to evacuate the heat from the core and can prevent, shut or affect the presence of a planetary magnetic field. The buoyancy and fate of molten material in such bodies can thus influence the magnetic history of the planet. Future observations of Mercury-like planets accreted near their star and the detections of their magnetic signatures could provide constraints on their inner state and partial melting histories.

在太阳系（地球，水星，月球，火星）中的几个碲化行星体上已经检测到剩余的磁化和活跃磁场，这表明在行星形成的早期阶段和可变寿命中存在活跃的核心动力。在控制核心动力产生可能性的因素中，周围硅酸盐地幔的动力学及其相关的热学性质至关重要。外套控制着核心的热量散发，因此控制着早期热驱动发电机的可能性。对于地幔较厚的行星（与超临界瑞利数相关），地幔对流有效地消除了地心热量，并且可能有早期的热力驱动发电机。在对面，地幔薄的行星（与次临界瑞利数相关）可能仅通过扩散来排空内部热量，这使得早期的热力驱动的动力学变得困难。在太阳系内，水星就是这种制度的潜在例子。在整个行星半径比上，其较小的地幔厚度可能是其较小的轨道半轴所固有的，因此，在靠近恒星的地面物体中可能无处不在。

为了限制热驱动发电机在“类汞”行星（即具有大的Rc / R）上的相似性，我们提供了各种固体，玻璃状和熔融样品的新热扩散率测量值。在多砧装置实验中，在2 GPa的压力和高达1700 K的温度下，我们在圆柱样品上应用了Angstrom方法。估计了具有不同熔体分数的固体和部分熔融橄榄岩的热扩散率和电导率，以及玄武岩和流纹玻璃的热扩散率和电导率融化。我们的研究表明，尽管所研究的成分范围很广，但熔体具有相似的热性能。熔体的热导率比固体低得多，几乎降低了一个数量级：1.70（±0.19）W / m / K，相对于0.18（±0.01）W / m / K（0.40（±0））。03）W / m / K分别用于高温橄榄岩和各种熔体。部分熔融样品介于两者之间，并且根据熔体分数和固/熔体织构提出了几种预测规律。

使用我们的结果对类似水星的行星生成发电机的热通量进行前向计算，我们可以量化地幔融化对热驱动发电机产生的影响。糊状的地幔和部分融化的存在会大大降低地幔将热量从岩心中抽散的能力，并且会阻止，关闭或影响行星磁场的存在。因此，此类物体中熔融材料的浮力和命运会影响行星的磁历史。对类似水星的行星的进一步观察表明它们的恒星附近增生，并且对它们的磁学特征的检测可能会限制它们的内部状态和部分融化历史。