Giovanni Cassini, the man who discovered four of the largest moons in the world, was the first to observe the Martian polar ice caps. The connection to Earth's own ice caps was established when Sir William Herschel recorded his own observations. The southern cap grew and shrunk due to seasonal changes in the planet Mars.
Scientists have learned a lot more about the polar deposits with the development of telescopes and robotic explorers. The southern cap is mostly composed of frozen carbon dioxide, which is unlike the northermost ice sheet. The glaciers of carbon dioxide ice have been carving features in the southern polar region for more than 600,000 years, and are currently moving.
The leader of the research team was an assistant professor of Earth and Space Science at York University in Toronto, who is also a Canada Research Chair in Planetary Science. He was joined by scientists from the Institute of Low-Temperature Science and the Hokkaido University in Japan.
The MRO confirmed the presence of carbon dioxide glaciers in the southern polar region in 2011. Scientists noted that they were flowing like glaciers of water ice on Earth, based on the surface features they carved in their wake. Smith described it in a recent press release.
“Approximately 600,000 years ago, CO2 ice started forming at the Martian south pole. Due to climate cycles, the ice has increased in volume and mass several times, interrupted by periods of mass loss through sublimation. If the ice had never flowed, then it would mostly be where it was originally deposited, and the thickest ice would only be about 45 meters thick. Instead, because it flowed downhill into basins and spiral troughs – curvilinear basins – where it ponded, it was able to form deposits reaching one kilometer thick.”
The portion of the ice cap composed of water ice appears to be stationary at high altitudes. Scientists investigated the strength properties of the carbon dioxide glaciers to find out why they were collapsing. Their results showed that carbon dioxide ice flows were 100 times faster than water ice glaciers.
The CO2 ice behaves like glaciers here on Earth, which makes the water ice cap appear stationary. These are large!
Smith and his colleagues used the NASA Ice Sheet and Sea-Level System Model to model the glacier's movements. They found that typical methods weren't moving the carbon dioxide glaciers on the surface of Mars. The flow rates peaked about 400,000 years ago when the deposition was at its best. Smith said that the flow rate of the glaciers is currently in a slow period since their ice is decreasing in mass.
“Atmospheric deposition would put the ice in a pattern we don’t see. It would be much more evenly spread and thinner. What the glacier interpretation provides is a mechanism to move the ice from high places, into the lower basins that are also at lower [latitudes].
“If atmospheric deposition were the only process acting on the ice, then most of it would be found at the highest latitude and highest elevation. That’s just not the case. The ice is flowing downhill into basins, much like water flows downhill into lakes. Only glacial flow can explain the distribution we found in 2018.”
Smith and his team identified several surface features that are very good analogues for features seen on glaciers. These include topographic profiles, crevasses, and compression ridges, which provided a basis to compare with their adapted-ISSM models.
Earth, Mars, and Pluto are the only bodies in the Solar System that have actively flowing ice. There are many icy bodies in the Solar System, including the larger satellites that circle Jupiter, Neptune, and other planets. Many of the same bodies have regular exchanges between their interiors and surfaces.
Many of these bodies will have glaciers of their own made of substances like carbon monoxide, ammonia, and methane, which could behave in even more exotic ways! In the coming years, scientists will be able to test these theories thanks to missions like the Enceladus Orbiter, which will explore two major satellites that have interior oceans and may even support life. Evidence of how these moons formed and evolved could be provided by the dynamics of their icy surfaces.
The paper that describes their findings was published in the journal JGR Planets.
Further reading on the topic of PSI.
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