Martian North Polar Vortex creates a layer of seasonal ozone, say planetary scientists
The polar vortex is a consequence of the Martian seasons, which occur because the axis of the planet is tilted at an angle of 25.2 degrees, according to Dr. Kevin Olsen of the University of Oxford and his colleagues from Latmos, the CNRS, the Space Research Institute, the open university and the Jet of Nasa jet laboratory.
View in perspective of the northern ice cap of March and its distinctive dark hollows forming a spiral pattern. The view is based on the images taken by Mars Express of ESA and generated using altitude data from the Altimeter Laser Mars Orbiter on board the NASA Global Surveyor of NASA. Image credit: ESA scientific team / DLR / FU Berlin / NASA / MGS / MOLA.
“The atmosphere inside the polar vortex, near the surface about 30 km high, is characterized by extreme cold temperatures, about 40 degrees Celsius colder than outside the vortex,” said Dr. Olsen.
“At such freezing temperatures, the small water vapor in the atmosphere freezes and is deposited on the ice cap, but this leads to consequences on the ozone in the vortex.”
Usually, ozone is destroyed by reacting with molecules produced when ultraviolet light breaks down water vapor.
However, with all the missing water vapor, there is nothing to react to ozone. Instead, ozone is able to accumulate in the vortex.
“Ozone is a very important gas on Mars – it is a very reactive form of oxygen and tells us how fast the chemistry occurs in the atmosphere,” said Olsen.
“By understanding the quantity of ozone and how variable it is, we know more about how the atmosphere has changed over time, and even if Mars once had a layer of protective ozone as on earth.”
Rosalind Franklin Rover of ESA, which should currently be launched in 2028, will seek evidence of past life on Mars.
The possibility that Mars once had a layer of ozone protecting the surface of the planet from the deadly influx of ultraviolet radiation from space would increase the chances that life could have survived Mars billions of years ago.
The polar vortex is a consequence of the seasons of March, which occur because the axis of the planet is tilted at an angle of 25.2 degrees.
Just like on Earth, the end of northern summer sees an atmospheric vortex developing on the North Pole of March and last until spring.
On Earth, the polar vortex can sometimes become unstable, lose its shape and go down to the south, bringing colder weather to the middle latitudes.
The same can happen to the Mars polar vortex, and in doing so, it offers the possibility of probe its interior.
“Because winters at the North Pole in Mars know total darkness, as on earth, they are very difficult to study,” said Dr. Olsen.
“By being able to measure the vortex and determine whether our observations are inside or outside the dark vortex, we can really say what is happening.”
The suite of atmospheric chemistry aboard the gas orbiter trace of ESA studies the Martian atmosphere by looking at the member of the planet when the sun is on the other side of the planet and shines in the atmosphere.
The wavelengths to which sunlight is absorbed give the molecules present in the atmosphere and the height above the surface.
However, this technique does not work in the total darkness of the Martian winter when the sun does not rise on the North Pole.
The only opportunities to erase inside the vortex are when it loses its circular shape but, to know exactly when and where it happens, requires additional data.
For this, the researchers turned to the instrument of Sounding Climate Mars on the NASA Mars recognition orbiter to measure the extent of the vortex via temperature measurements.
“We sought a sudden drop in temperature – a certain sign of being inside the vortex,” said Dr. Olsen.
“The comparison of ACS observations with the results of the Sono-Sonder of the Mars climate shows clear differences in the atmosphere inside the vortex compared to the outside.”
“It is a fascinating opportunity to know more about the chemistry of the Martian atmosphere and how the conditions change during the polar night to allow the ozone to accumulate.”
Scientists presented their results this month EPSC-DPS2025 joint meeting In Helsinki, Finland.
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K. Olsen and al. 2025. What is happening inside the Mars North polar vortex? EPSC summary 18: EPSC-DPS2025-1438; DOI: 10.5194 / EPSC-DPS2025-1438
