In October 2014, the close encounter between Mars and comet Siding Spring produced a transient ionized layer in the upper atmosphere composed primarily of Mg⁺ and Fe⁺ ions. The layer was detected by instruments on three spacecraft, including the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) on Mars Express. Analyses of the MARSIS data indicated the transient layer persisted up to 19 h after the comet's closest approach. We report MARSIS observations that suggest the transient layer lasted at least 7 days—and potentially as long as 32 days—after closest approach. During this period, the transient layer was mostly confined to a narrow latitude range between 20°N and 60°N and a longitude range spanning 275°E to 95°E. Since this period coincided with a highly active Sun, we discuss how solar flares may have contributed to the layer's prolonged lifetime.

中文翻译：

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彗星壁板弹簧引起的火星大气瞬变电离层寿命延长

2014年10月，火星与Siding Spring彗星之间的紧密相遇在高层大气中产生了一个瞬态电离层，该层主要由Mg ⁺和Fe ^+组成离子。该层被三架航天器上的仪器探测到，包括火星地下雷达和电离层测深仪（MARSIS）。对MARSIS数据的分析表明，在彗星最接近的方法之后，过渡层持续了19小时。我们报告了MARSIS的观察结果，表明过渡层在最接近的方法之后至少持续了7天，甚至可能长达32天。在此期间，过渡层主要被限制在20°N至60°N的较窄纬度范围和275°E至95°E的经度范围内。由于这一时期恰好是活跃的太阳，因此我们讨论了太阳耀斑如何有助于延长该层的寿命。