Using data from NASA’s MAVEN spacecraft, a team from West Virginia University found evidence that the planet’s atmosphere is protected from the solar wind even in the absence of a strong magnetic field, also known as the Zwanwolf effect.
The Zwan-Wolf effect was first reported in 1976 and was observed only in the planetary magnetosphere, not in the atmosphere. However, the findings reported in Nature Communications observed effects in Mars’ atmosphere, providing a new understanding of how the sun interacts with planetary bodies in the solar system.
The Sun continuously emits a stream of plasma known as the solar wind. When this plasma stream encounters large objects, such as planets or comets, it is deflected around them, much like the flow of water around rocks in a stream.
“But,” says planetary scientist Christopher Fowler of West Virginia University, “the water in that stream is relatively dense, so the physical collisions of water molecules colliding with each other and rocks determine the direction of the water. In contrast, the environment in space is so tenuous that solar wind particles don’t collide with each other. Instead, electromagnetic forces control how particles are deflected around these objects.”
“Very interesting wiggles”
When the solar wind curves around a planet with a strong magnetic field like Earth, the Zwan-Wolf effect is observed because the plasma is squeezed by electromagnetic forces passing through “flux tubes” (regions of space created by parallel magnetic field lines).
“This compression helps move the solar wind plasma around the planet, making the plasma at the front of the planet less dense,” Fowler said.
“By discovering this effect in the atmosphere of Mars, we are discovering new ways in which the sun interacts with and influences the planets in our solar system. It’s amazing to think that a solar eruption could disturb the atmosphere of Mars 142 million miles away.”
Fowler found “very interesting changes” in the 2023 data from MAVEN, NASA’s Mars Atmosphere and Evolution mission. “We had no idea it would have this kind of effect because it had never been observed in a planet’s atmosphere before.”
Observing this rare phenomenon may help protect future explorers from the effects of space weather
“We think this effect can always occur in the Martian atmosphere, but it’s usually a very small effect so our instruments aren’t sensitive enough to detect it,” Fowler said.
“The solar storm actually hit Mars hard and disrupted the entire space environment around Mars. This likely amplified the Zwan Wolf effect, making it observable during this period. We were lucky to be in the right place at the right time with MAVEN to see this.”
“We observed these signatures all the way to the lowest altitudes that MAVEN sampled, suggesting that they are affecting the atmosphere even below the spacecraft,” Fowler said. “Understanding how these space weather phenomena affect our solar system is important not only for keeping robotic and potentially human spacecraft safe in the future, but also for protecting the space assets we rely on for everyday technology here on Earth.”
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