Scientists have put on their Sherlock Holmes caps to unravel a mystery that has puzzled researchers for decades – the origin of the huge layer of CO2 layered ice and water ice at the south pole of Mars and its relationship to CO2 in the atmosphere.
One of the main hypotheses is that these layers are pressed against each other when the Mars axis tilts towards the Sun and deviates from it, and simulation models published in the new study support this idea.
The ice cap in question is about a kilometer deep and is believed to contain as much CO2 as there is in the entire atmosphere of Mars today, and a combination of factors led to this unusual layered structure.
“Usually, when you run a model, you don't expect the results to be that close to what you observe,” says Peter Buehler, planetary scientist at NASA's Jet Propulsion Laboratory.
“But the thickness of the layers determined by the model is in excellent agreement with radar measurements from orbiting satellites.”
What makes the South Pole ice cap so strange is that it shouldn't actually be there – water ice is more thermally stable and darker than CO2 ice, so scientists expect CO2 ice to destabilize.
According to the new model, three factors prevented this from happening: the change in the tilt of the Mars axis as it rotates around the Sun, differences in the way the two types of ice are reflected by sunlight, and the change in atmospheric pressure that occurs when CO2 ice turns into gas.
Over time, the changing climate of the Red Planet changed atmospheric pressure – increasing it, as Leighton and Murray predicted in the 1960s.
Scientists estimate this has been going on for about 510,000 years – since the last period when all the CO2 would have been sublimated into the Martian atmosphere.
“Our determination of the history of large pressure drops on Mars is fundamental to understanding the evolution of the climate on Mars, including the history of stability and liquid water near the surface of Mars,” says Buehler.
The study was published in the journal Nature Astronomy.
