Most bodies in the solar system have rocky mantles and metallic cores, with an icy layer on top. But Saturn’s moon Iapetus stands out from other moons with its mostly ice composition. There are bits of rock and carbonaceous material that make half the moon appear darker than the other, but this seems to be only a surface feature.
Moreover, Ice on Iapetus is different from ice found on Earth. Because the moon’s temperature can get as low as 185 degrees Celsius (300 degrees Fahrenheit), the moon’s ice is very hard and very dry.
Recently, long landslides spotted on Iapetus, could help provide clues to similar movements of material on Earth. Scientists studying the icy satellite have determined that flash heating could cause falling ice to travel 10 to 15 times farther than previously expected on Iapetus.
Slow-moving ice creates a lot of friction, so when the ice falls from high places, scientists expected that it would behave much like rock on Earth does. Instead, they found that it traveled significantly farther than predicted.
How far a landslide runs is usually related to how far it falls, lead scientist Kelsi Singer of Washington University, explains. Most of the time, debris of any type loses energy before traveling twice the distance it fell from. But on Iapetus, the pieces of ice move 20 to 30 times as far as their falling height.
Flash heating could be providing that extra push.
Flash heating occurs when material falls so fast that the heat doesn’t have time to dissipate. Instead, it stays concentrated in small areas, reducing the friction between the sliding objects and allowing them to travel faster and farther than they would under normal conditions.
“They’re almost acting more like a fluid,” Singer says.
On Iapetus, falling material has a good chance of reaching great speeds because there are a number of great heights to fall from. The moon hosts a ring of mountains around its bulging equator that can tower as high as 20 km. (12 miles), and the longest run-outs discovered are associated with the ridge and with impact-basin walls.
Extended landslides can be found on Mars and Earth, but are more likely to be composed of rock than ice. Despite the differences in materials, scientists believe there could be a link between the long-tumbling debris on all three bodies.
“We think there’s more likely a common mechanism for all of this, and we want to be able to explain all of the observations,” Singer says.
Giant landslides stretching as far as 50 miles litter the surface of Iapetus. Singer and her team identified 30 such displacements by studying images taken by NASA’s Cassini spacecraft.
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