A new way the Sun and space weather can change planetary atmospheres
In December 2023, a solar storm struck Mars and revealed something no one had anticipated: a plasma-squeezing phenomenon, known as the Zwan-Wolf effect, unfolding in the planet's unshielded upper atmosphere. NASA's MAVEN spacecraft, long stationed in Martian orbit to study how the Sun erodes worlds without magnetic armor, captured the event in real time — the first such observation beyond Earth's own magnetosphere. The discovery invites a deeper reckoning with how exposed planets endure the Sun's relentless breath, and what that endurance means for the story of atmospheres, habitability, and time.
- A rare and powerful solar storm in December 2023 created conditions strong enough for MAVEN to catch a plasma phenomenon scientists had never seen operating in a bare planetary atmosphere.
- The Zwan-Wolf effect — previously confined to the study of Earth's magnetically shielded environment — was now compressing charged particles in a place with no magnetic field at all, upending assumptions about where such physics could occur.
- Researchers believe the effect may happen on Mars routinely, but most occurrences are too faint to detect, meaning this single storm-amplified event may represent the tip of a largely invisible iceberg.
- The finding extends the question outward to Venus, another unshielded world, suggesting that solar-atmospheric dynamics on magnetically naked planets may be far more complex and active than previously understood.
- MAVEN's broader mission — tracing how Mars lost its atmosphere and its liquid water over billions of years — now gains a new chapter, one that maps the ongoing, real-time ways the Sun continues to sculpt planetary fates.
In December 2023, a powerful solar storm struck Mars and handed scientists an unexpected gift. NASA's MAVEN spacecraft, orbiting the Red Planet since 2014, detected the Zwan-Wolf effect — a compression of plasma in the upper atmosphere caused by the solar wind — somewhere it had never been seen before. A team led by Christopher Fowler of the University of West Virginia published the findings in Nature Communications, describing how MAVEN's instruments caught the event as it unfolded.
What makes the discovery striking is that Mars has no magnetic field. The Zwan-Wolf effect had previously been studied only within Earth's magnetosphere, where a global magnetic shield shapes the interaction between solar wind and charged particles. On Mars, there is no such shield — yet the same squeezing mechanism appeared in the ionosphere, that upper layer where solar radiation frees electrons from gas molecules and leaves behind a charged plasma. Fowler described the surprise plainly: no one had expected this effect could even occur in an atmosphere, and its presence opens up physics that hasn't yet been explored.
Researchers believe the effect likely occurs on Mars more often than this single detection suggests, but routine events are probably too faint for current instruments to register. The December storm was exceptional enough to produce a detectable signal — a fortunate coincidence that cracked open a new line of inquiry.
The implications reach beyond Mars. Venus, which also lacks a magnetic field, may experience similar dynamics under solar bombardment. Venus has no plate tectonics, which prevents the internal heat circulation needed to generate a magnetic field despite having a liquid iron core. Understanding how the Zwan-Wolf effect operates on Mars could illuminate how Venus' atmosphere responds to the Sun as well.
MAVEN was originally sent to answer a foundational question: how did Mars lose the thick atmosphere it once had? The spacecraft confirmed that the solar wind, acting over billions of years, gradually stripped it away — taking with it the conditions that once allowed liquid water to exist on the surface. The Zwan-Wolf discovery adds a new dimension to that long story, showing that the Sun's influence on unprotected worlds is still being written, and still being understood.
In December 2023, something unexpected happened in the thin upper reaches of Mars' atmosphere. A powerful solar storm struck the planet, and NASA's MAVEN spacecraft—orbiting Mars since 2014—detected a phenomenon that scientists had never before observed on the Red Planet: the Zwan-Wolf effect, a kind of atmospheric squeezing caused by the solar wind compressing charged particles in the ionosphere.
The discovery matters because Mars has no magnetic field to shield it from space weather, the way Earth's magnetic field does. Yet somehow, the same plasma-squeezing mechanism that researchers had studied for years in Earth's magnetosphere was happening in Mars' bare atmosphere. A team led by Christopher Fowler, an assistant research professor at the University of West Virginia, published their findings in Nature Communications, describing how MAVEN's instruments captured this rare event in real time.
The ionosphere—that region of the upper atmosphere where solar radiation has knocked electrons loose from gas molecules, leaving behind a soup of positive ions and negative electrons—became the stage for this effect. When the solar wind, that constant stream of charged particles flowing from the Sun, collided with Mars' ionosphere during the December storm, it compressed the plasma in a way that had never been directly observed there before. Fowler noted the surprise in the discovery: "No one expected that this effect could even occur in the atmosphere. 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."
Researchers suspect the Zwan-Wolf effect may happen regularly on Mars, but those ordinary occurrences are too faint for current instruments to catch. The December 2023 solar storm was powerful enough to create a signature strong enough for MAVEN to detect. This single observation opens a window into how planets without magnetic fields respond to solar activity—a question with implications beyond Mars alone.
Venus, the only other planet in the solar system with an atmosphere but no magnetic field, could experience similar effects. Venus lacks a magnetic field because it has no plate tectonics, which means heat cannot circulate through its interior the way it does on Earth. That circulation, called convection, is one of two requirements for generating a magnetic field. Venus does have a liquid iron core—the other requirement—but without convection, no field forms. Understanding how the Zwan-Wolf effect operates in Mars' atmosphere may shed light on how Venus' atmosphere behaves under solar bombardment.
MAVEN itself has been on this mission since November 2013, arriving at Mars in September 2014. Its original purpose was to solve a long-standing mystery: how did Mars lose its atmosphere? The spacecraft confirmed what scientists had long suspected—that the solar wind, over billions of years, stripped away much of the Martian atmosphere, leaving behind the thin, cold world we see today. That loss of atmosphere also meant Mars could no longer hold liquid water on its surface, transforming it from a potentially habitable world into the desert planet it is now. The discovery of the Zwan-Wolf effect adds another layer to that story, revealing new ways the Sun shapes planetary atmospheres, even in the absence of a protective magnetic shield.
Citações Notáveis
No one expected that this effect could even occur in the atmosphere. 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.— Dr. Christopher Fowler, University of West Virginia, lead author of the study
A Conversa do Hearth Outra perspectiva sobre a história
So Mars has no magnetic field at all—it's completely exposed to the solar wind?
Completely. That's what makes this discovery so striking. We've known about the Zwan-Wolf effect in Earth's magnetosphere for years, but finding it in Mars' bare ionosphere suggests the physics works differently than we thought.
Why does it matter that it happened during a solar storm specifically?
The effect probably happens all the time on Mars, but too weakly to detect. The December 2023 storm was violent enough that MAVEN could actually see it. It's like the difference between hearing a whisper and hearing someone shout—same voice, different volume.
And this tells us something about Venus too?
Yes. Venus is in the same boat as Mars—no magnetic field, but it has an atmosphere. If we understand how solar wind interacts with Mars' ionosphere, we get clues about what's happening in Venus' atmosphere right now.
Does this change how we think about Mars losing its water?
It adds texture to the story. We already knew the solar wind stripped Mars' atmosphere away over time. Now we see another mechanism—this plasma squeezing—that shows just how dynamic and relentless that interaction is.
What happens next? Does MAVEN keep watching for this?
MAVEN went silent in December 2025, so we don't know yet. But this discovery means future missions to Mars will be looking for this effect, trying to understand how often it occurs and what role it plays in atmospheric loss.