NASA's MAVEN spacecraft has recorded something Mars has never shown before, which is the Zwan-Wolf effect. It's a process long known in Earth's magnetosphere but now seen for the first time in a planetary atmosphere. The findings, published in Nature Communications, came from data collected in December 2023 during a solar storm. Instead of helping deflect the solar wind as it does at Earth, the effect at Mars appears to "squeeze" the upper atmosphere, reshaping how space weather interacts with the Red Planet.
"When investigating the data, I all of a sudden noticed some very interesting wiggles," Christopher Fowler, a research assistant professor at West Virginia University in Morgantown and lead author of the study, said as quoted by NASA. "I would never have guessed it would be this effect, since it's never been seen in a planetary atmosphere before."
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First identified in 1976, the Zwan-Wolf effect describes how charged particles get compressed along magnetic field lines called flux tubes. At Earth, this compression helps divert the solar wind around our protective magnetic shield.
Mars doesn't have a global magnetic field. That's why the MAVEN team didn't expect to find the effect there. Yet the spacecraft's instruments picked up telltale "wiggles" in the ionosphere, the electrically charged layer of the Martian atmosphere below about 200 km.
MAVEN, short for Mars Atmosphere and Volatile Evolution, found that during the December 2023 solar storm, charged particles in Mars' ionosphere were being squeezed and redistributed around the planet. The effect was occurring deep in the atmosphere, where there's a significant population of ions, not just in the near-space environment around the planet.
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The new Zwan-Wolf observations add another piece to that puzzle, revealing a way the atmosphere can be compressed and redistributed during space weather events.
"No one expected that this effect could even occur in the atmosphere," said Fowler. "That's what makes this even more exciting. It introduces interesting physics that we haven't yet explored and a new way the Sun and space weather can change the dynamics in the Martian atmosphere."
The finding could help scientists learn more about Mars' climate. "Knowing how space weather interacts with Mars is essential," said Shannon Curry, the principal investigator of MAVEN and research scientist at the Laboratory for Atmospheric Space Physics at the University of Colorado Boulder. "The MAVEN team continues making new discoveries with our datasets and finding these links between our host star and the Red Planet."
