Discovery of Dry Ice on Mars Reveals Clues About the Planet’s Atmosphere

An enormous underground deposit of frozen carbon dioxide was recently discovered at the south pole of Mars, suggesting that the atmosphere of the planet was much dustier and stormier than it is today. The report comes from scientists at the Southwest Research Institute in Boulder, Colorado. The discovery has prompted a comparison to the climate of the American Dust Bowl of the 1930s, but on an even greater scale.
Scientists were made aware of the presence of carbon dioxide under the surface of the planet due to the appearance of the Martian south pole. Described as “swiss cheese terrain” by scientists, the surface was covered with round depressions, suggesting that underground carbon dioxide deposits had evaporated.
The frozen carbon dioxide reservoir, which has also been referred to as a dry ice lake, is located at the south pole of the planet. The CO2 deposit has a volume of nearly 3,000 cubic miles, roughly the same size as Lake Superior. The frozen material was discovered by the Mars Reconnaissance Orbiter, which probed beneath the crust of the planet using shallow radar. Researchers have been aware of the presence of dry ice on the planet for some time, although it was believed to be in much smaller quantities. Scientists speculate that at least some of the frozen carbon dioxide was once a part of the Martian atmosphere, making it much denser than it is today.
In the past, the southern pole of Mars was exposed to sunlight when Mars’ axis tilted. This allowed some of the frozen carbon dioxide to melt, releasing some of it into the atmosphere and making it thicker. The release of the carbon dioxide would also cause more dust to be released into the air, causing severe storms. Other times, though, the carbon dioxide would simply go back into the ground as part of the seasonal cycle. Today, dust storms are less frequent because the carbon dioxide is frozen under the surface. The atmosphere is thinner because there is less CO2 creating air pressure. This decreases the strength of the wind, causing less frequent and less severe dust storms.
Even though Mars was more prone to storms during this time, the thicker atmosphere allowed for the presence of liquid water on some parts of the planet. When the planet was very young, it was much warmer and wetter, and the surface was filled with gullies, canyons, and rivers. Mars today is in stark opposition to this; the planet is extremely dry and frigid. The current atmosphere of Mars is primarily comprised of carbon dioxide and is extremely thin at less than one percent of Earth’s atmosphere. The Martian atmosphere is comprised of roughly 95 percent carbon dioxide, while Earth’s much thicker atmosphere is made up of .04 percent carbon dioxide.
The discovery of the frozen carbon dioxide is 30 times more carbon dioxide than scientists were expecting to find. The presence of the dry ice deposit may be a clue as to why the atmosphere of Mars is so thin. If released, the carbon dioxide has the potential to double the atmosphere of Mars, although it would be unable to considerably raise the planet’s temperatures or allow water to pool.
Jeffrey Plaut, a member of the discovery team, has described the discovery of the frozen carbon dioxide deposit as a “buried treasure.” The mysteries of Mars, particularly its atmosphere, continue to fascinate scientists. NASA has plans to study the upper Martian atmosphere and the phenomenon of how gases are lost in space with a new spacecraft starting in 2013.
Photo credit: sos.noaa.gov/datasets/solar_system/mars.html

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