Mars polar vortex traps cold and builds seasonal ozone layer
At the EPSC-DPS2025 Joint Meeting in Helsinki, scientists reported that Mars’s north polar vortex traps air about 40°C (72°F) colder than its surroundings, creating conditions for ozone to build up in the darkness of winter.
A view of the north pole of Mars, created by taking images as seen by the European Space Agency’s Mars Express spacecraft and applying topographic data from the Mars Orbiter Laser Altimeter that was on board NASA’s now defunct Mars Global Surveyor mission. Credit: ESA/DLR/FU Berlin/NASA MGS MOLA Science Team.
Measurements show that the atmosphere inside the north polar vortex, from the surface up to 30 km (19 miles), is about 40°C (72°F) colder than outside. These extreme temperatures freeze out what little water vapour exists, depositing it onto the ice cap.
Normally, ozone is destroyed when ultraviolet sunlight breaks down water vapour, releasing molecules that react with ozone. With water vapour removed, that destruction stops. Ozone is then able to accumulate in the dark, cold vortex.
Ozone is a reactive form of oxygen. On Earth, it forms a protective layer that shields the surface from ultraviolet radiation. On Mars, it acts as a tracer of atmospheric chemistry, showing how fast reactions occur and how conditions have changed over time.
Why the discovery matters for habitability
This seasonal ozone layer raises questions about whether Mars once had a more permanent ozone shield. A thicker atmosphere in the past may have supported a protective layer like Earth’s, blocking harmful ultraviolet light and creating a safer surface for potential microbial life.
The European Space Agency’s Rosalind Franklin rover, scheduled to launch in 2028, will search for signs of ancient life in subsurface samples. Evidence that Mars once had an ozone shield would strengthen the case that the surface environment was more hospitable billions of years ago.
How scientists detected ozone inside the vortex
The team led by Dr Kevin Olsen of the University of Oxford used the Atmospheric Chemistry Suite on ESA’s ExoMars Trace Gas Orbiter to analyze the martian atmosphere. This instrument identifies gases by studying how sunlight is absorbed when passing through the atmosphere at the limb of the planet.
During the polar night, this method is not possible, since no sunlight reaches the north pole. Instead, the team relied on data from the Mars Climate Sounder on NASA’s Mars Reconnaissance Orbiter. By measuring temperature changes, they identified the vortex boundary.
A sharp temperature drop between 10 and 20 km (6–12 miles), defined as colder than −103°C (−153°F), marked the edge of the vortex. Inside this region, water vapour nearly vanished and ozone concentrations rose. This confirmed the link between ozone buildup, extreme cold, and the absence of water vapour.
The planetary mechanics behind the vortex
Mars has an axial tilt of 25.2°, close to Earth’s 23.4°, which produces seasons. At the end of northern summer, a polar vortex forms and remains through autumn and winter until spring sunlight returns.
Like Earth’s vortex, which can sometimes destabilize and spill cold air southward, Mars’s vortex can deform and shift. These distortions allow orbiters to glimpse its interior, offering rare opportunities to study its chemistry.
A natural laboratory for Mars’s climate history
Each winter, the polar vortex becomes a chemical chamber, isolating air masses, removing water, and cutting off sunlight. Inside, conditions are preserved that reveal how atmospheric chemistry operates in extreme cold.
For scientists, the vortex offers a chance to understand Mars’s climate cycles and their connection to long-term atmospheric loss. Comparing the martian vortex with Earth’s helps refine models of how tilted planets regulate their seasonal climates.
References:
1 What goes on inside the Mars north polar vortex? – Kevin Olsen – Euro Planet – https://doi.org/10.5194/epsc-dps2025-1438 – July 9, 2025
2 EPSC-DPS2025: Mars’s Chilly North Polar Vortex Creates a Seasonal Ozone Layer – Euro Planet – September 17, 2025
I’m a science journalist and researcher at The Watchers, contributing to the Epicenter edition, where I cover peer-reviewed scientific research and emerging discoveries across Earth and space sciences. With a background in astronomy and a passion for environmental science, I’ve worked in shark and coral conservation in Fiji, conducting reef and shark-behavior research, contributing to mangrove restoration, and earning PADI Open Water and Coral Reef Certifications. I bring a blend of scientific rigor and storytelling to illuminate the discoveries shaping our planet and beyond.
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