近日，瑞典空间物理研究所的Qi Zhang及其研究团队取得一项新进展。经过不懈努力，他们证实火星的感应磁层会退化。相关研究成果已于2024年9月18日在国际权威学术期刊《自然》上发表。

本文研究表明，当火星处的锥角较小时，感应磁层会发生退化。在日照侧没有激波，仅有微弱的侧翼激波。此时会出现横流羽流，并且双极场会驱动行星离子向上游移动。采用4°锥角的混合模拟结果，与火星大气与挥发物演化任务以及火星快车的观测结果相符。退化的感应磁层是复杂且尚未得到充分研究的对象。离子逃逸导致的大气损失等过程中的次要效应仍有待进一步研究。

据悉，行星与恒星风之间的相互作用会导致大气损失，因此对于行星大气的演化至关重要。我们太阳系中的行星通常与太阳风相互作用，而太阳风的速度与嵌入的恒星磁场之间形成较大的夹角。对于没有固有磁场的行星，这种相互作用会产生感应磁层以及行星前方的弓形激波。然而，当太阳风速度与太阳风磁场之间的夹角（即锥角）较小时，相互作用则大不相同。

附：英文原文

Title: Mars’s induced magnetosphere can degenerate

Author: Zhang, Qi, Barabash, Stas, Holmstrom, Mats, Wang, Xiao-dong, Futaana, Yoshifumi, Fowler, Christopher M., Ramstad, Robin, Nilsson, Hans

Issue&Volume: 2024-09-18

Abstract: The interaction between planets and stellar winds can lead to atmospheric loss and is, thus, important for the evolution of planetary atmospheres. The planets in our Solar System typically interact with the solar wind, whose velocity is at a large angle to the embedded stellar magnetic field. For planets without an intrinsic magnetic field, this interaction creates an induced magnetosphere and a bow shock in front of the planet. However, when the angle between the solar wind velocity and the solar wind magnetic field (cone angle) is small, the interaction is very different. Here we show that when the cone angle is small at Mars, the induced magnetosphere degenerates. There is no shock on the dayside, only weak flank shocks. A cross-flow plume appears and the ambipolar field drives planetary ions upstream. Hybrid simulations with a 4° cone angle show agreement with observations by the Mars Atmosphere and Volatile Evolution mission and Mars Express. Degenerate, induced magnetospheres are complex and not yet explored objects. It remains to be studied what the secondary effects are on processes like atmospheric loss through ion escape.

DOI: 10.1038/s41586-024-07959-z

Source: https://www.nature.com/articles/s41586-024-07959-z