火星电离层中的电流系统特征研究
Characterizing the current systems in the Martian ionosphere
AI总结：
本研究利用MAVEN任务八年数据识别出火星电离层中由太阳风、大气中性风分别驱动的两类电流系统，揭示了上下层因素对火星电离层动力学的共同作用，推进了对无磁行星电离层电流的认知。
摘要：
当太阳风与无磁行星的电离层相互作用时，会感应出形成感应磁层的电流。这些电流及其相关磁场在控制带电粒子运动方面发挥着关键作用，这对于理解行星离子的逃逸过程至关重要。与已有充分研究记录的磁层电流系统不同，无磁行星的电离层电流系统仍鲜为人知，这限制了对从恒星到这类行星的电动力学能量传输的量化研究。本研究利用火星大气与挥发物演化任务（Mars Atmosphere and Volatile EvolutioN, MAVEN）长达八年的观测数据，探究了火星电离层电流的全球分布特征。我们在火星电离层中识别出两种截然不同的电流系统：一种与太阳风电场方向一致，但在垂直于电场方向上呈现半球不对称性；另一种则与年平均中性风的流动模式相对应。我们提出，这两种电流系统分别由太阳风和大气中性风驱动。研究结果表明，火星电离层动力学同时受到来自下方的中性风和来自上方的太阳风的共同影响，凸显了无磁行星上电流系统的复杂性与独特性。
英文摘要：
When the solar wind interacts with the ionosphere of an unmagnetized planet, it induces currents that form an induced magnetosphere. These currents and their associated magnetic fields play a pivotal role in controlling the movement of charged particles, which is essential for understanding the escape of planetary ions. Unlike the well-documented magnetospheric current systems, the ionospheric current systems on unmagnetized planets remain less understood, which constrains the quantification of electrodynamic energy transfer from stars to these planets. Here, utilizing eight years of data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we investigate the global distribution of ionospheric currents on Mars. We have identified two distinct current systems in the ionosphere: one aligns with the solar wind electric field yet exhibits hemispheric asymmetry perpendicular to the electric field direction; the other corresponds to the flow pattern of annually-averaged neutral winds. We propose that these two current systems are driven by the solar wind and atmospheric neutral winds, respectively. Our findings reveal that Martian ionospheric dynamics are influenced by the neutral winds from below and the solar wind from above, highlighting the complex and intriguing nature of current systems on unmagnetized planets.
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