Unveiling Mars’s Harsh Winter Atmosphere
New observations have shed rare light on Mars’s north polar vortex during its long, shadowed winter. Researchers studying the Red Planet’s atmosphere found that the conditions inside the vortex are far more extreme than those outside, with darkness enabling an unusual surge in ozone. The findings were presented at the EPSC-DPS2025 Joint Meeting in Helsinki, highlighting how the polar night creates a unique laboratory for planetary chemistry.
Inside the North Polar Vortex: A World of Extreme Cold
From the surface up to about 30 kilometers high, the atmosphere inside the Martian northern polar vortex runs a frigid regime roughly 40 degrees Celsius colder than regions outside the vortex. This dramatic temperature difference is tied to Mars’s seasonal tilt and the prolonged darkness at the pole, which suppresses the usual daytime heating that distributes heat and light more evenly across the planet.
The Chemistry Behind the Ozone Surge
Water Vapor Condensation and Ozone Destruction
In these frigid conditions, the small amount of water vapor present in the Martian atmosphere tends to condense and settle on the ice cap. This condensation has a profound effect on atmospheric chemistry. On Earth and Mars alike, ozone is partially destroyed by reactions involving ultraviolet sunlight and water vapor. When water vapor is scarce, these destructive pathways are limited, allowing ozone to accumulate inside the vortex rather than being broken down.
Why Ozone Matters on Mars
Ozone is a reactive form of oxygen that serves as a tracer for how fast atmospheric chemistry is progressing. By measuring how much ozone builds up and how variable it is, scientists can infer past and present atmospheric processes on Mars. Researchers also raise the intriguing possibility that Mars may have once possessed a protective ozone layer that shielded its surface from ultraviolet radiation, potentially impacting the planet’s habitability billions of years ago.
How Scientists Probe the Polar Night
The investigation relies on data from two space-based assets. The ExoMars Trace Gas Orbiter (TGO), equipped with the Atmospheric Chemistry Suite (ACS), observes Mars by looking at the limb when sunlight passes through the atmosphere. The specific wavelengths absorbed by atmospheric molecules reveal which gases are present and at what altitudes. But ACS cannot operate during the polar night, so researchers needed a complementary approach.
To detect when the vortex is inside versus outside the dark region, the team used temperature measurements from NASA’s Mars Reconnaissance Orbiter (MRO) and its Mars Climate Sounder. A sudden drop in temperature signals that a measurement is likely inside the vortex. By combining ACS and Climate Sounder data, scientists observed clear differences between the atmosphere inside the vortex and that outside, offering a rare window into Martian atmospheric chemistry under polar night conditions.
Implications for Mars’s History and Future Missions
These findings provide critical clues about how Mars’s atmosphere behaves under extreme, sunless winters and how ozone chemistry responds to the planet’s unique conditions. Understanding ozone dynamics helps scientists reconstruct past atmospheric states and assess whether Mars might have hosted an ozone layer in its ancient history. This knowledge feeds into broader questions about the planet’s climate evolution and its potential to have supported life.
Looking ahead, Europe’s ExoMars program aims to push these inquiries further with the Rosalind Franklin rover, planned for launch in 2028. The mission will search for signs of ancient life and, by extension, may offer additional context about early Martian atmospheric conditions and the role ozone could have played in shielding or exposing the surface to ultraviolet radiation.
Research and Outlook
The study, titled “What goes on inside the Mars north polar vortex?” and published as part of EPSC-DPS2025, synthesizes observations from multiple instruments to illuminate the dynamic chemistry of Mars’s polar night. As missions continue to orbit and land on Mars, scientists hope to refine models of atmospheric processes and deepen our understanding of how a planet with a thin air envelope interacts with sunlight, darkness, and the mysteries of ozone.
Reference: Olsen et al., EPSC-DPS2025, 2025. DOI: 10.5194/epsc-dps2025-1438
