![Average ion velocity and magnetic field distributions near the ICB. (A) The center-of-mass velocity of heavy ions in the XZMSE plane, averaged over −1 RM < YMSE < 1 RM. (B) Proton velocity. (C) Velocity shear between protons and heavy ions. (D) Magnetic field strength. (E) Angle between the magnetic field and the X�⃗ MSEin the YZMSE plane, averaged over −1.5 RM < XMSE < 0.5 RM. Black arrows in (A) to (C) indicate velocity directions. Black curves in (A) to (D) mark the nominal locations of the bow shock and ICB. The black shaded sphere in (E) denotes the planetary shadow. -- [physics.space-ph]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/08/Simultaneous.png?fit=1200%2C676&ssl=1)
[physics.space-ph] Atmospheric ion escape driven by the solar wind is a key process controlling the long-term loss of the Martian atmosphere. Localized plasma clouds can carry substantial fluxes of planetary ions away from Mars, representing episodes of bulk escape.
However, their origin has remained unclear due to the absence of simultaneous upstream measurements. Using joint observations from the MAVEN and Tianwen-1 missions, which provide real-time upstream monitoring, we present direct evidence that these plasma clouds are nonlinear wave packets generated by the Kelvin-Helmholtz instability (KHI).
The spatial scale of KH waves is constrained for the first time via two-point measurements. Ion fluxes within plasma clouds are one to two orders of magnitude higher than those in typical steady-state escape channels. Our results indicate that KHI is an important process for solar wind coupling to planetary upper atmospheres and plays a crucial role in shaping atmospheric ion escape for unmagnetized planets.
Chi Zhang, Chuanfei Dong, Gangkai Poh, Jasper Halekas, Xuanye Ma, Ruhunusiri Suranga, Kathleen G. Hanley, Han-Wen Shen, Hongyang Zhou, Xinmin Li, Liang Wang, Jiawei Gao, Shannon Curry, Christian Mazelle
Subjects: Space Physics (physics.space-ph); Earth and Planetary Astrophysics (astro-ph.EP); Plasma Physics (physics.plasm-ph)
Cite as: arXiv:2608.03780 [physics.space-ph] (or arXiv:2608.03780v1 [physics.space-ph] for this version)
https://doi.org/10.48550/arXiv.2608.03780
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Related DOI:
https://doi.org/10.1126/sciadv.aed9072
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Submission history
From: Chi Zhang
[v1] Tue, 4 Aug 2026 15:02:14 UTC (2,023 KB)
https://arxiv.org/abs/2608.03780
Astrobiology, exoplanet,
