Mars Atmosphere Stripped by Solar Wind Waves, New Study Finds

Mars is a cold, dry world today, but the Red Planet once possessed a thicker atmosphere and surface liquid water. Understanding how that transformation occurred has long puzzled planetary scientists. Unlike Earth, which enjoys the protective shield of a global magnetic field generated by its churning molten iron core, Mars lost its equivalent shield approximately four billion years ago. What remains of its magnetic protection is limited to scattered patches of ancient magnetized crust in the southern hemisphere—far too weak to deflect the Sun’s continuous stream of charged particles.

Without a robust global shield, the solar wind sweeps directly into the upper Martian atmosphere. Scientists previously identified two pathways through which it strips atmospheric ions away: a dayside plume where particles are accelerated outward, and a nightside tail where ions drift off into space. But a Boston University-led research team has now proven the existence of a third, highly dynamic mechanism that operates in sharp, concentrated bursts.

Two Spacecraft Solve an Observational Puzzle at Mars

For years, a fundamental observational barrier blocked researchers from confirming how large plasma clouds formed in the upper atmosphere. A single spacecraft could not observe the undisturbed solar wind upstream on Mars while also measuring the atmospheric ions escaping into space. Without that independent upstream baseline, scientists could not distinguish whether escaping plasma clouds were triggered externally by solar wind gusts or generated locally at the atmospheric boundary.

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That limitation vanished when researchers combined simultaneous observations from NASA’s MAVEN orbiter and China’s Tianwen-1 orbiter. Tianwen-1 tracked the parameters of the undisturbed solar wind before it reached the planet, while MAVEN recorded the escaping ions just above the atmosphere. By pairing the two missions, the team ruled out incoming solar wind gusts as the direct trigger and pinned the phenomenon on fluid dynamics.

Kelvin-Helmholtz Waves Whip Up Planetary-Scale Plasma Clouds

The physical mechanism operating at Mars is familiar terrestrial physics scaled up to a planetary level. When wind blows across the surface of water, the velocity difference between fast-moving air and slower water generates ripples that curl into rolling vortices. The same fluid-dynamics process occurs wherever two fluids in relative motion share a boundary.

At Mars, the boundary is the outer edge of the upper atmosphere where fast solar wind protons meet slower Martian atmospheric ions. Instead of a uniform flow, the solar wind stirs the outer atmospheric boundary, creating enormous plasma disturbances known as Kelvin-Helmholtz waves. Growing wave crests trap pockets of ionized Martian gas and fling them outward as large plasma clouds.

Published in Science Advances, the study notes that ion escape rates measured inside these plasma clouds reach between 10 and 100 times higher than the rates observed in the steady-state dayside plume and nightside tail channels. Whether these intense, burst-mode events account for a major share of total cumulative atmospheric loss over geological timescales remains an open question for future computer simulations.

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Uneven Atmospheric Loss and Future Exploration

The atmospheric draining process does not affect the planet uniformly. Researchers discovered that the Kelvin-Helmholtz wave activity concentrates primarily on one side of the planet, depending on the direction of the solar wind electric field.

Chi Zhang, lead author of the study at Boston University’s Center for Space Physics, emphasized that subsequent work will target the specific conditions favoring the formation and growth of these waves. Understanding how much they contribute to total atmospheric escape will require advanced numerical modeling and a larger array of spacecraft.

While the MAVEN mission moves toward its closeout stage, researchers look to upcoming projects to carry forward the work.