Mars may be losing its atmosphere through a process that looks surprisingly familiar: the same kind of rolling instability that creates waves and vortices when wind blows across water. A new study led by Boston University researchers has found that the solar wind can generate enormous waves along the outer boundary of Mars’ upper atmosphere, helping propel clouds of atmospheric ions into space. The discovery offers a clearer explanation for how the Red Planet gradually lost much of the atmosphere and surface water it may once have possessed.
The solar wind is a continuous stream of electrically charged particles released by the Sun. Moving primarily as a plasma—a state of matter composed of free electrons and ions—it travels through the Solar System at hundreds of kilometers per second. Earth is protected from much of this flow by its global magnetic field, which diverts charged particles around the planet. Mars, however, no longer has a strong planet-wide magnetic shield. Its upper atmosphere is therefore exposed to direct interaction with the solar wind, allowing atmospheric particles to be heated, accelerated, and carried away into space.
The new research, published in Science Advances, identifies Kelvin–Helmholtz waves as an important mechanism in this atmospheric loss. These waves form when two fluids or plasmas move past one another at different velocities. The velocity difference creates shear along the boundary between them, causing the interface to roll, twist, and develop wave-like structures. On Earth, the same instability can appear where wind flows across water or at the boundaries between layers of air moving at different speeds. At Mars, the process occurs where the solar wind meets the planet’s ionized upper atmosphere.
The researchers combined measurements from NASA’s Mars Atmosphere and Volatile Evolution mission, known as MAVEN, with observations from China’s Tianwen-1 spacecraft. Tianwen-1 monitored the solar wind upstream of Mars, before it was altered by interaction with the planet. At the same time, MAVEN measured atmospheric ions escaping from the region around Mars. This two-spacecraft arrangement allowed the team to compare changing solar-wind conditions with the behavior of escaping particles in near real time.
That capability was crucial because a single spacecraft cannot easily measure both the undisturbed solar wind far from Mars and the atmospheric ions leaving the planet. Without simultaneous upstream measurements, it is difficult to determine whether changes in atmospheric escape are caused by solar-wind variations or by processes occurring within the Martian environment itself. By linking the two data sets, the researchers were able to trace the formation of large plasma structures back to the interaction between the solar wind and the upper atmosphere.
The study focuses on enormous clouds of plasma containing ions from Mars’ atmosphere. These clouds represent a form of “bulk escape,” in which groups of atmospheric particles are removed together rather than escaping individually. Scientists had previously proposed several possible explanations for the origin of these structures, but direct observational evidence had been limited. The new results indicate that Kelvin–Helmholtz waves can gather and reshape atmospheric plasma, creating conditions that allow substantial quantities of ions to be swept away.
The process is not distributed evenly around Mars. According to the researchers, the waves and associated ion escape are concentrated on one side of the planet, depending on the direction of the solar-wind electric field. In a plasma, an electric field can exert forces on charged particles and influence the direction in which they drift. Because ions and electrons respond to electromagnetic fields, the orientation of the solar wind can determine where the boundary instability develops most strongly and where atmospheric material is most efficiently transported into space.
The findings provide a direct physical connection between solar-wind conditions, Kelvin–Helmholtz waves, and enhanced atmospheric escape. Over geological time, repeated loss of atmospheric particles could have contributed to the transformation of Mars from a potentially warmer and wetter world into the cold, dry planet observed today. The mechanism described in the study is not necessarily the only process responsible for atmospheric loss, but it may help explain how large amounts of material can be removed from the upper atmosphere during favorable solar-wind conditions.
The researchers now aim to determine when these waves are most likely to form, how quickly they grow, and how much atmospheric material they remove. Answering those questions will require additional spacecraft observations and high-resolution numerical simulations of plasma behavior around Mars. MAVEN is entering the closeout stage of its mission, but NASA’s ESCAPADE mission is expected to provide a new opportunity to investigate how the solar wind drives atmospheric escape. The same instability may also occur at other worlds without strong global magnetic fields, including some exoplanets whose atmospheres are exposed directly to their stars.
Subject of Research: Not applicable
Article Title: Simultaneous Mars-Orbit Observations Reveal Kelvin–Helmholtz–Instability–Driven Bulk Atmospheric Ion Escape
News Publication Date: 31-Jul-2026
Web References: https://www.science.org/doi/10.1126/sciadv.aed9072
References: Science Advances, DOI: 10.1126/sciadv.aed9072
Image Credits: Chi Zhang, Boston University
Keywords
Mars, solar wind, atmospheric escape, Kelvin–Helmholtz waves, plasma, MAVEN, Tianwen-1, planetary science, space weather, Mars atmosphere, exoplanets
