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Simultaneous Mars-orbit observations reveal Kelvin-Helmholtz instability-driven bulk atmospheric ion escape
Chi Zhang1, Chuanfei Dong1,2, Gangkai Poh3,4
1Center for Space Physics and Department of Astronomy, Boston University, Boston, MA, USA.
Science Advances
|July 31, 2026
Summary
Localized plasma clouds, driven by the Kelvin-Helmholtz instability (KHI), are key to Martian atmospheric ion escape. Joint MAVEN and Tianwen-1 data reveal KHI
Area of Science:
- Planetary Science
- Space Physics
- Atmospheric Science
Background:
- Atmospheric ion escape is crucial for Mars' long-term atmospheric evolution.
- Localized plasma clouds represent significant, yet poorly understood, atmospheric ion loss events.
- Previous studies lacked simultaneous upstream measurements to identify the origin of these clouds.
Purpose of the Study:
- To identify the origin of localized plasma clouds responsible for Martian atmospheric ion escape.
- To provide direct evidence linking these clouds to a specific instability mechanism.
- To constrain the spatial scales of the underlying wave phenomena.
Main Methods:
- Joint observations from the Mars Atmosphere and Volatile Evolution (MAVEN) and Tianwen-1 missions.
- Real-time upstream monitoring of solar wind and plasma conditions.
- Two-point measurements to constrain the spatial scale of wave packets.
Main Results:
- Direct evidence confirms plasma clouds are nonlinear wave packets generated by the Kelvin-Helmholtz instability (KHI).
- The spatial scale of KH waves was constrained for the first time using two-point measurements.
- Ion fluxes within these plasma clouds are significantly higher (1-2 orders of magnitude) than in steady-state escape channels.
Conclusions:
- The Kelvin-Helmholtz instability (KHI) is a primary driver for localized atmospheric ion escape on Mars.
- KHI plays a crucial role in the solar wind coupling to upper atmospheres of unmagnetized planets.
- Understanding KHI is vital for modeling atmospheric evolution and ion loss on Mars and similar planets.
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