双航天器观测揭示火星磁鞘中广泛存在的等离子体射流

中文摘要 AI 辅助

行星磁鞘中的等离子体射流是瞬态的、高动态压力结构，能够强烈扰动下游磁层并调节太阳风能量传输。尽管最近在火星上发现了它们，但其形成机制和全球出现范围仍缺乏约束。利用火星大气与挥发物演化任务（MAVEN）和天问一号的双航天器观测，我们表明磁鞘射流发生在整个火星磁鞘中，这与地球形成鲜明对比——在地球上，射流的发生受到行星际磁场方向的强烈控制，并且主要局限于准平行激波区域。我们提出，这种广泛分布与火星延伸的氢冕有关，氢冕产生拾取离子，这些离子在弓形激波上游驱动质子回旋波。由于这一机制对于任何嵌入恒星风中的具有延伸冕（或外逸层）的天体都是通用的，这一发现对彗星和其他小天体处的太阳风相互作用，以及无磁场类地系外行星的空间环境具有意义。这些结果表明，磁鞘射流的形成不仅受外部太阳风强迫控制，还受行星固有属性控制，指出了在无磁场世界中太阳风-行星耦合的一条先前未被认识到的途径。

英文摘要

Plasma jets in planetary magnetosheaths are transient, high dynamic pressure structures capable of strongly perturbing downstream magnetospheres and modulating solar wind energy transfer. Although recently identified at Mars, their formation mechanisms and global occurrence remain poorly constrained. Using dual-spacecraft observations from Mars Atmosphere and Volatile EvolutioN (MAVEN) and Tianwen-1, we show that magnetosheath jets occur throughout the Martian magnetosheath, in striking contrast to Earth where jet occurrence is strongly controlled by interplanetary magnetic field orientation and largely confined to quasi-parallel shock regions. We propose that this widespread distribution is linked to Mars' extended hydrogen corona, which generates pickup ions that drive proton-cyclotron waves upstream of the bow shock. Because this mechanism is generic to any body with an extended corona (or exosphere) embedded in a stellar wind, this finding bears on solar-wind interactions at comets and other small bodies, and on the space environments of unmagnetized terrestrial exoplanets. These results indicate that magnetosheath jet formation can be governed not only by external solar wind forcing but also by intrinsic planetary properties, pointing to a previously unrecognized pathway for solar wind-planet coupling at unmagnetized worlds.

发表机构

• Boston University（波士顿大学）
• Institute for Advanced Study, Princeton（普林斯顿高等研究院）
• The Johns Hopkins University Applied Physics Laboratory（约翰斯·霍普金斯大学应用物理实验室）

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