MAVEN observes particle squeeze on Mars

NASA said this week that its MAVEN orbiter has recorded the first observations at Mars of the Zwan-Wolf effect, a process in which charged particles are squeezed along magnetic structures known as flux tubes. The finding was published May 18 in *Nature Communications* and described the effect in Mars’ ionosphere, deep in the upper atmosphere below 200 kilometers. Scientists had previously observed the effect at Earth, where it has been studied for decades, but not in a planetary atmosphere. Christopher Fowler, a research assistant professor at West Virginia University and lead author of the study, said the signal first appeared as “very interesting wiggles” in MAVEN data from December 2023. Fowler said he did not expect the pattern to be the Zwan-Wolf effect because it had “never been seen in a planetary atmosphere before.” NASA’s account said the event was detected when a large solar storm hit Mars and amplified a process that may otherwise be too weak for MAVEN to resolve clearly. (science.nasa.gov) ### What exactly did MAVEN see at Mars? NASA said MAVEN observed charged particles in the Martian ionosphere being compressed and redistributed along magnetic structures, in the same broad pattern associated with the Zwan-Wolf effect at Earth. The agency described the process as particles being squeezed “like toothpaste coming out of a tube” along flux tubes. At Earth, that effect helps deflect solar wind around the planet. At Mars, NASA said, it appears to squeeze the atmosphere and shape how space weather interacts with it. (science.nasa.gov) The *Nature Communications* paper said the observations show the Zwan-Wolf effect occurring at an unmagnetized planet that lacks a dipole magnetic field. That makes Mars an unusual setting for the phenomenon, because the planet does not have the kind of global magnetic shield that protects Earth. ### Why is Mars an unexpected place to find this? Mars lacks a global magnetic field, and NASA said that difference changes how the planet responds to solar wind and space weather. (science.nasa.gov) Instead of a stable, planet-wide magnetic shield, Mars has an induced magnetosphere created by the interaction between the solar wind and the ionosphere. NASA said that induced field can change greatly in size and shape during major solar-wind events. (nature.com) The new observations placed the effect in the ionosphere below 200 kilometers, where electrically charged particles are abundant. NASA said the measurements indicate the squeezing process may be present more often, but that the December 2023 storm likely strengthened it enough for the spacecraft to detect it clearly. ### Why were scientists looking at December 2023 data? (science.nasa.gov) December 2023 was the period in which researchers found the signal while reviewing MAVEN measurements, according to NASA’s account of the study. The agency said the spacecraft was flying through the atmosphere when the team noticed unusual magnetic-field fluctuations tied to a large solar storm at Mars. Those conditions gave researchers a way to study how the Martian atmosphere reacts when solar activity intensifies. (science.nasa.gov) MAVEN, short for Mars Atmosphere and Volatile EvolutioN, has been orbiting Mars since September 21, 2014. NASA says the mission’s central goal is to understand the Martian upper atmosphere and how the planet has lost part of that atmosphere over time. The new result fits that mission by adding another observed mechanism linking solar activity, magnetic structure and atmospheric behavior. ### Where does this leave the mission now? (science.nasa.gov) NASA’s MAVEN mission page says the orbiter remains an active Mars mission focused on the upper atmosphere, even as the agency has also been reviewing a separate loss-of-signal episode disclosed in March 2026. The new Mars result was posted through NASA Science and tied directly to the May 18 publication in *Nature Communications*, which names Fowler and his co-authors as the next reference point for follow-up work on the effect. (science.nasa.gov)