In 1666, the famous Italian astronomer and mathematician Giovanni Cassini (the man who discovered four of Saturn’s largest moons) observed the Martian polar caps for the first time. However, it was not until the late 18th century, when Sir William Herschel recorded his own observations, that the connection to Earth’s own ice sheets was made. In his later treatise,On the remarkable apparitions in the polar regions of the planet Mars(1784), noted how the south cap grew and shrunk due to seasonal changes.
With the development of modern telescopes and robotic explorers, scientists have learned much more about these polar deposits. In 2011, they learned that unlike the northernmost ice sheet, the southern ice sheet is largely made up of frozen carbon dioxide (aka “dry ice”). According to new research by the Institute of Planetary Sciences (PSI), glaciers of carbon dioxide ice have been move and sculpt functions in the southern polar region for over 600,000 years – and are on the move right now!
The research team was led by isaac smithformer PSI researcher and Assistant Professor of Earth and Space Sciences at York University in Toronto (where he also holds a Canada Research Chair in planetary sciences). He was joined by geologists, glaciologists and engineers from PSI, York University, Institute of Low Temperature Sciences and arctic research center at Hokkaido University in Japan and NASA’s Jet Propulsion Laboratory (JPL).
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The presence of carbon dioxide glaciers in the south polar region of Mars has been first confirmed in 2011 by the Mars Reconnaissance Orbiter (MRO). Along with data obtained by ESA’s Mars Express, the scientists noted that they flowed much like water-ice glaciers do here on Earth, based on the surface features they carved in their wake. As Smith described in a recent PSI Press release:
“About 600,000 years ago, CO2 ice has begun to form at the Martian south pole. Due to climatic cycles, the ice increased several times in volume and mass, interrupted by periods of loss of mass by sublimation. If the ice had never sunk, it would mostly be where it was originally deposited, and the thickest ice would only be about 45 meters thick. Instead, because it flowed downward into spiral basins and troughs – curvilinear basins – where it accumulated, it was able to form deposits up to a kilometer thick.
These observations also showed that the part of the ice sheet composed of water ice appears to be stationary, remaining at high altitude. In previous research, to which Smith helped contribute while still at PSI, scientists studied the resistance properties (i.e. flow laws) of carbon dioxide glaciers to determine why this was happening. Their results indicated that in the kinds of conditions that exist around the southern polar region, carbon dioxide ice flows were almost 100 times faster than water ice glaciers.
For this, they concluded that CO2 ice behaves like glaciers here on Earth, which makes the slow-moving ice sheet appear stationary. “Glaciers have enough mass that if sublimated they would double the atmospheric pressure of the planet,” Smith added, quoting a 2018 article by Than Putzig, senior scientist at PSI and co-author of this article. “The longest glacier is about 200 kilometers long and about 40 kilometers wide. These are great!”
For this study, Smith and his colleagues relied on NASA Ice sheet and sea level system model (ISSM) to model the movements of the glacier. Once adapted to conditions on the surface of Mars and with CO2, they found that typical methods did not displace carbon dioxide glaciers. They found that while activity continues, flows peaked about 400,000 years ago, when deposition was at its peak. Since their ice mass is currently shrinking, Smith said, glacier flow is currently in a “slow period”:
“Atmospheric deposition would place the ice in a pattern that we don’t see. It would be much more evenly distributed and thinner. What the glacier interpretation provides is a mechanism to move ice from high places to lower basins which are also at lower levels. [latitudes].
“If atmospheric deposition were the only process acting on the ice, then most of it would be at the highest latitude and highest altitude. This is simply not the case. Ice flows down into ponds, much like water flows down into lakes. Only glacial flow can explain the distribution we found in 2018.”
This work is bolstered by additional research by Smith and his team, which identified several surface features that are very good analogues for features seen on terrestrial glaciers. These include topographic profiles, crevices and compression ridges, which provided a basis for comparison with their adapted ISSM models. These findings could also inform future planetary investigations and point to more “Earth-like” glacial activity.
To date, Earth, Mars, and Pluto are the only bodies in the solar system known to have actively flowing ice, ranging from water ice to CO2 with frozen nitrogen. But there are many other icy bodies in the solar system, including the larger satellites orbiting Jupiter, Saturn, Uranus and Neptune, and the growing number of smaller planets discovered in the Kuiper Belt. Many of these same bodies experience regular exchanges between their interiors and their surfaces (endogenous resurfacing, cryovolcanism, etc.).
Many of these bodies will likely have their own glaciers composed of substances like carbon monoxide, ammonia and methane, which could behave in even more exotic ways! In the years to come, scientists will be able to test these theories with missions like the European Clipper and the Enceladus Orbiter, which will explore two major satellites that have interior oceans and may even harbor life. The dynamics of their icy surfaces could provide further evidence for the formation and evolution of these moons.
The article describing their findings recently appeared in the journal JGR Planets, a publication overseen by the American Geological Union (AGU).
Further reading: psi