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Changes in Mars’ atmosphere are driven by enormous CO2 ice cap at its pole

We’re just starting to learn about how complex the atmosphere of Mars is. We know that it is primarily composed of carbon dioxide, but there are also smaller amounts of oxygen and methane there whose levels fluctuate over time. And all the way back in 1966, scientists theorized that the planet’s stable cap of carbon dioxide at its pole could have planet-wide effects on the atmosphere.

Now, a new study has looked at the carbon dioxide ice deposit on Mars’ south pole and found that it does indeed appear to affect global atmospheric pressure. This is due to several factors: The fact that Mars’ atmosphere is very thin, with a surface pressure of 0.6% that of Earth, and the fact Mars wobbles on its axis by up to 10 degrees as it orbits the sun, so at some times its poles are exposed to more sunlight than at other times.

Together, these factors mean that the carbon dioxide ice on the south pole is occasionally exposed to direct sunlight, leading to sublimation — where the carbon dioxide turns from a solid to a gas without passing through the liquid stage. The pumping of relatively large amounts of carbon dioxide gas into the atmosphere could have profound effects on the planet over the long term.

The Martian pole
The Martian pole NASA/JPL/Malin Space Science Systems

These changes would be enough to swing the pressure of Mars’ atmosphere from down to one-quarter of where it is today to all the way up to twice where it is today, although this change would happen slowly, over tens of thousands of years.

Researchers looked at the ice cap and the layers of carbon dioxide ice and water ice which comprise it, and they formulated a model of how the layers could have developed over time. When they compared their model to the real findings, they found an excellent match.

“Usually, when you run a model, you don’t expect the results to match so closely to what you observe,” researcher Peter Buhler said in a statement. “But the thickness of the layers, as determined by the model, matches beautifully with radar measurements from orbiting satellites.”

This gives strong evidence that the sublimation of carbon dioxide ice is indeed changing the atmospheric pressure over time. And that helps us to understand how Mars’ climate has changed in the past and will continue to change in the future. “Our determination of the history of Mars’s large pressure swings is fundamental to understanding the evolution of Mars’s climate, including the history of liquid water stability and habitability near Mars’s surface,” Buhler explained.

The findings are published in the journal Nature Astronomy.

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