Most of the large rocky bodies in the solar system display evidence of past and/or current magnetic activity, driven by thermochemical convection in an electrically conducting fluid layer. The discovery of a large number of extrasolar planets motivates the search for magnetic fields beyond the solar system. While current observations are limited to providing planetary radii and minimum masses, studying the evolution of exoplanets' magnetic fields and their interaction with the atmosphere can open new avenues for constraining interior properties from future atmospheric observations. Here, we investigate the evolution of massive rocky planets (0.8 − 2 M_Earth) with different bulk and mantle iron contents. Starting from their temperature profiles after accretion, we determine the structure of the core and model its subsequent thermal and magnetic evolution over 5 Gyr. We find that the planetary iron inventory and distribution strongly affect core structure, evolution, and the lifetime of a magnetic field. Planets with large bulk and mantle iron contents tend to feature large solid inner cores, which can grow up to the liquid outer core radius, shutting down any pre‐existing magnetic activity. Consequently, the longest dynamo lifetimes (∼ 4.25 Gyr) are obtained for massive planets with intermediate iron inventories. The smaller inner core radii and the chemical buoyancy fluxes introduced by the presence of light impurities can extend the magnetic field lifetimes to more than 5 Gyr. While the calculated magnetic fields are too weak to be detected by ground facilities, indirect observations may provide valuable insights into exoplanetary dynamos.

中文翻译：

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系外核的结构和热演化

太阳系中的大多数大型岩石体都显示出过去和/或当前的磁活动的证据，这些活动是由导电流体层中的热化学对流驱动的。大量太阳系外行星的发现促使人们寻找太阳系以外的磁场。虽然目前的观测仅限于提供行星半径和最小质量，但研究系外行星磁场的演化及其与大气的相互作用可以为限制未来大气观测的内部特性开辟新途径。在这里，我们研究了大型岩石行星（0.8 − 2 M_地球）具有不同的散装和地幔铁含量。从吸积后的温度曲线开始，我们确定了磁芯的结构，并对其随后在5 Gyr内的热和磁演化建模。我们发现行星铁的存量和分布强烈影响铁心的结构，演化和磁场的寿命。具有大体积和地幔铁含量的行星往往具有较大的固体内核，这些内核可以长到液体外核半径，从而关闭任何先前存在的磁活动。因此，对于具有中等铁含量的大型行星，可以获得最长的发电机寿命（约4.25 Gyr）。较小的内芯半径和由于存在轻杂质而引入的化学浮力通量可以将磁场寿命延长到5 Gyr以上。