水星的地壳磁化强度表明古代发电机更强
Mercury's Crustal Magnetization Indicates a Stronger Ancient Dynamo
AI总结：
研究通过模拟表明水星古代发电机磁场强度远强于现今，排除两种机制，支持其由近完全对流核心产生的结论。
摘要：
水星是太阳系中除地球外唯一拥有活跃发电机磁场（赤道表面约200纳特斯拉）的类地行星。此外，水星约39亿至37亿年前的地壳被强烈磁化（30公里高度处约10纳特斯拉），表明存在过古代发电机。然而，古代发电机的磁场强度及其产生机制尚不明确。为解决这一问题，我们开展了三维磁流体动力学模拟，模拟古代太阳风与行星磁场的相互作用，并结合地壳热演化与磁化模型。结果显示，地壳磁化很可能由偶极场产生，赤道表面强度至少约2000纳特斯拉；若发电机反转频率超过每百万年一次，强度可能高达约30000纳特斯拉。如此强的磁场很可能排除了37亿年前的太阳风反馈机制和热发电机机制，相反，我们的结果与古代发电机由近完全对流的核心产生的结论相符。
英文摘要：
Mercury is the only terrestrial planet in the solar system other than Earth with an active dynamo magnetic field (~200 nT at the equatorial surface). Furthermore, Mercury's ~3.9-3.7-billion-year-old (Ga) crust is strongly magnetized (~10 nT at ~30-km altitude), indicating the presence of a past dynamo. However, the strength of the past dynamo field and the mechanism that generated it are unknown. To address this, we performed three-dimensional magnetohydrodynamic simulations of the ancient solar wind interaction with the planetary field coupled with crustal thermal evolution and magnetization models. We show that the crustal magnetization was likely produced by a dipole field with equatorial surface strength of at least ~2,000 nT and possibly as high as ~30,000 nT for a dynamo with a reversal frequency greater than once per million years. Such strong fields likely exclude both the solar wind feedback and thermoelectric dynamo mechanisms at 3.7 Ga ago. Instead, our results are compatible with the past dynamo being generated by a nearly fully convective core.
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