Department of Earth and Planetary Science, University of California, Berkeley, CA, 94720, USA.
École Normale Supérieure de Lyon, Université Lyon 1, Laboratoire de Géologie de Lyon, CNRS UMR5276, Lyon Cedex 07, 69364, France.
Nat Commun. 2018 Sep 24;9(1):3883. doi: 10.1038/s41467-018-06432-6.
Super-Earths are extremely common among the numerous exoplanets that have been discovered. The high pressures and temperatures in their interiors are likely to lead to long-lived magma oceans. If their electrical conductivity is sufficiently high, the mantles of Super-Earth would generate their own magnetic fields. With ab initio simulations, we show that upon melting, the behavior of typical mantle silicates changes from semi-conducting to semi-metallic. The electrical conductivity increases and the optical properties are substantially modified. Melting could thus be detected with high-precision reflectivity measurements during the short time scales of shock experiments. We estimate the electrical conductivity of mantle silicates to be of the order of 100 Ω cm, which implies that a magnetic dynamo process would develop in the magma oceans of Super-Earths if their convective velocities have typical values of 1 mm/s or higher. We predict exoplanets with rotation periods longer than 2 days to have multipolar magnetic fields.
超级地球在已发现的众多系外行星中极为常见。其内部的高压高温很可能导致长期存在的岩浆海洋。如果它们的电导率足够高，超级地球的地幔将产生自己的磁场。通过从头算模拟，我们表明，在熔化过程中，典型地幔硅酸盐的行为从半导体转变为半金属。电导率增加，光学性质发生实质性改变。因此，在冲击实验的短时间尺度内，可以通过高精度反射率测量来检测到熔化。我们估计地幔硅酸盐的电导率约为 100 Ω·cm，这意味着如果超级地球的对流速度具有典型值 1mm/s 或更高，那么在其岩浆海洋中将会发展出磁发电机过程。我们预测自转周期超过 2 天的系外行星将具有多极磁场。
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