Mars is slowly losing parts of its atmosphere to space, and scientists have discovered that the process may be driven by giant waves created where the solar wind meets the planet’s upper atmosphere.
The new research, led by Boston University, shows that these waves act much like wind blowing across the surface of a lake, helping carry charged particles away from Mars.
The study was published in Science Advances.
The Sun constantly releases a stream of fast-moving charged particles called the solar wind.
Earth is protected from most of this flow by its strong global magnetic field, which acts like a shield around the planet.
Mars, however, lost its global magnetic field billions of years ago.
Without this protection, the solar wind can directly interact with the Martian atmosphere, gradually removing particles and allowing them to escape into space.
Scientists have known for many years that Mars is losing its atmosphere, but exactly how this happens has remained a mystery. The new study provides strong evidence for one important process behind this slow loss.
The researchers found that when the solar wind sweeps past Mars, it creates huge ripples at the boundary of the planet’s upper atmosphere.
These ripples are called Kelvin-Helmholtz waves, a type of wave that forms whenever two layers moving at different speeds slide past one another. A familiar example can be seen when wind blows across the surface of water, creating rolling waves and swirling patterns.
In space, the same kind of motion happens between the fast-flowing solar wind and the gases surrounding Mars. As these waves grow, they create large clouds of electrically charged gas, known as plasma. These plasma clouds help lift large numbers of atmospheric ions into space, increasing the rate at which Mars loses its atmosphere.
To make this discovery, the scientists combined observations from two different spacecraft. NASA’s MAVEN spacecraft measured the charged particles escaping from Mars, while China’s Tianwen-1 mission monitored the incoming solar wind before it reached the planet.
By comparing measurements from both spacecraft at the same time, the team was able to directly connect changes in the solar wind with the loss of atmospheric particles.
The study also revealed that this process is not the same everywhere around Mars. Instead, the giant waves and escaping plasma clouds tend to form on one side of the planet, depending on the direction of the solar wind’s electric field. This helps explain why atmospheric loss can vary from place to place.
The researchers now want to understand when these waves are most likely to appear, how they grow and how much they contribute to the long-term loss of Mars’ atmosphere. Answering these questions will require additional spacecraft observations and more detailed computer simulations.
Although NASA’s MAVEN mission is nearing the end of its operations, scientists are looking forward to new information from NASA’s ESCAPADE mission, which has already been launched and is expected to continue exploring how the solar wind affects Mars.
The findings may also help scientists study other worlds beyond our solar system. Planets without strong magnetic fields could experience similar atmospheric loss, making this research important for understanding how planetary environments change over billions of years.
Scientists believe Mars once had a much thicker atmosphere and liquid water on its surface, making it far more suitable for life than it is today.
By learning how the solar wind slowly stripped that atmosphere away, researchers hope to better understand the history of Mars and the evolution of planets throughout the universe.
