Structure and Thermal Evolution of Exoplanetary Cores
Structure and Thermal Evolution of Exoplanetary Cores
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DOI：
10.1029/2020je006724
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发表时间：
2020-10
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影响因子：
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通讯作者：
I. Bonati;M. Lasbleis;L. Noack
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文献类型：
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作者：
I. Bonati;M. Lasbleis;L. Noack
太阳系中的大多数大型岩石天体都显示出过去和/或当前磁活动的证据，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激发了对太阳系以外磁场的探索。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未来大气观测中限制内部特性开辟新途径。在这里，我们研究了具有不同体积和地幔铁含量的大质量岩石行星（0.8 − 2 MEarth）的演化。从吸积后的温度分布开始，我们确定了核心的结构，并对其随后超过 5 Gyr 的热和磁演化进行了建模。我们发现行星铁的库存和分布强烈影响核心结构、演化和磁场的寿命。体积和地幔铁含量较高的行星往往具有较大的固体内核，其可以生长到液体外核半径，从而关闭任何预先存在的磁活动。因此，具有中等铁库存的大质量行星获得了最长的发电机寿命（~ 4.25 Gyr）。较小的内核半径和轻杂质引入的化学浮力通量可以将磁场寿命延长至 5 Gyr 以上。虽然计算出的磁场太弱而无法被地面设施检测到，但间接观测可能会为了解系外行星发电机提供有价值的见解。
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 MEarth) 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.