Caltech study may have explained Martian atmosphere mystery

In the mid-1960s, scientists from Caltech, Robert B. Leighton, and Bruce C. Murray theorized about the carbon dioxide in the Martian atmosphere that was discovered on a flyby by Mariner IV. The scientists theorized that Mars could have a long-term stable polar deposit of carbon dioxide ice that could control the global atmospheric pressure.

A new Caltech study suggests that their theory may be correct. Carbon dioxide makes up 95% of the atmosphere of Mars. The Red Planet has a surface pressure of only 0.6% of the Earth's. The theory from Leighton and Murray was that atmospheric pressure could change in value as the planet wobbles on its axis in orbit around the sun.

That would expose the poles to more or less sunlight, and direct sunlight on the carbon dioxide ice in the poles leads to sublimation. Sublimation is the direct transition of a material from a solid to a gaseous state. The scientists predicted that atmospheric pressure would swing from one-quarter of the pressure of Mars' atmosphere today to twice that of today over cycles of tens of thousands of years.

The new model by Caltech researchers has provided key evidence to support that model. The team explored the existence of a mysterious feature of the south pole of Mars, a massive deposit of carbon dioxide ice and water ice in alternating strata. The layers extend to a depth of 1 km. The scientists say that the layer deposits have as much carbon dioxide as the entire Mars atmosphere today.

Scientists long thought that carbon dioxide ice couldn't survive when buried under water ice. However, the new Caltech model shows the layers could have evolved as a result of changing tilt of the planet's rotation, the difference in how water ice and carbon dioxide ice reflect sunlight, and an increase in atmospheric pressure caused by carbon dioxide ice sublimation. They think that the warmer periods cause the carbon dioxide ice to sublime, leaving behind the layers of more stable water ice.