Mars, often called the Red Planet due to its rusty iron oxide covered surface, is Earth’s smaller, colder neighbour. Orbiting the Sun at an average distance of 228 million kilometres, Mars shares remarkable similarities with Earth; a 24.6 hour day, polar ice caps, seasons driven by a 25.2 degree axial tilt, and evidence of ancient rivers and lakes that once flowed across its surface. Yet Mars today is a harsh world with a thin atmosphere just 1% the density of Earth’s, average temperatures of -63°C, and no liquid water on its surface. It has an incredibly thin atmosphere composed primarily of carbon dioxide (95%) which is so tenuous that liquid water cannot exist on the surface, yet it’s still thick enough to generate global dust storms.
Mars, the red planet (Credit : Kevin Gill)
Despite its thin atmosphere, Mars experiences dramatic seasonal weather patterns driven by its axial tilt. A team of researchers has recently been studying one of these seasonal events, the north polar vortex, a massive atmospheric circulation system similar to Earth’s polar vortex. They found that temperatures inside the vortex are 40°C colder than outside, creating conditions unlike anywhere else on the planet. A polar vortex is a large scale circular wind pattern that forms in the upper atmosphere around a planet’s polar regions. It’s a little like a massive spinning column of cold air that acts like an atmospheric fence, trapping cold air over the pole.
The polar vortex forms as a consequence of the Martian seasons, which occur because the planet’s axis is tilted at 25.2 degrees. This is very similar to Earth’s 23.5 degree tilt and just like on Earth, the end of northern summer sees an atmospheric vortex develop over Mars’s north pole and last through to the spring. What makes this discovery particularly interesting is the chemistry inside the vortex. Ordinarily, ozone on Mars is destroyed by reacting with molecules produced when ultraviolet sunlight breaks down water vapour.
A strong tropospheric polar vortex configuration in November 2013 (Credit : National Oceanic and Atmospheric Administration)
Instead, during Martian winters and at such cold temperatures, what little water vapour exists freezes out completely and deposits onto the ice cap. Meanwhile, the polar region descends into months of total darkness. Without water vapour and without sunlight to drive the usual destructive chemical reactions, ozone can build up to surprising levels.
“Ozone is a very important gas on Mars, it’s a very reactive form of oxygen and tells us how fast chemistry is happening in the atmosphere. By understanding how much ozone there is and how variable it is, we know more about how the atmosphere changed over time, and even whether Mars once had a protective ozone layer like on Earth.” – Dr. Kevin Olsen of the University of Oxford
It’s remarkable the team were able to make such progress in their study. The winters at the north pole of Mars experience total darkness so it’s quite difficult to study the vortex. Instead the team had to use two different spacecraft working together. One of them was the European Space Agency’s ExoMars Trace Gas Orbiter, which studies the Martian atmosphere by observing sunlight passing through the planet’s limb. But this technique alone doesn’t work so they combed this data with temperature measurements from NASA’s Mars Climate Sounder aboard the Mars Reconnaissance Orbiter.
This artist’s concept of NASA’s Mars Reconnaissance Orbiter features the spacecraft’s main bus facing down, toward the red planet (Credit : NASA/JPL/Corby Waste)
They team were able to look for a sudden drop in temperature which would be the telltale signs of a vortex. Studying the vortex has directly helped to understand more about the ozone levels on Mars and therefore whether the planet once had an ozone layer that protected the surface from ultraviolet radiation. If so, it increases the chance that life could perhaps once have existed on Mars billions of years ago.
Source : Mars’s Chilly North Polar Vortex Creates a Seasonal Ozone Layer