Planetary scientists discovered unexpected and enormous ice avalanches on Saturn’s moon Iapetus, half of which is light-colored while the other is dark. Its mountains are 12 miles in height, which is twice the height of Mount Everest.
Kelsi Singer, graduate student in earth and planetary sciences at Washington University in St. Louis, and the lead author of a new study published in the journal Nature Geoscience states that this isn’t something that they were expecting to find on Iapetus.
The icy landslides are something similar to long-runout ones on Earth that are known as sturzstroms. They can travel distances 20 to 30 times the height they fall from. Typical landslides only travel about twice the height they fall from. This implies that the Iapetus landslides were probably caused by objects impacting the moon’s surface.
Planetary scientists aren’t yet sure on exactly what mechanism allows them to travel so far, but possible candidates include riding on a cushion of trapped air, sliding on groundwater or mud, sliding on ice, or slipping caused by strong acoustic vibrations. Singer thinks that on Iapetus the landslides are caused by frictional heating of ice.
The researchers analyzed images taken by NASA’s Cassini spacecraft as it orbited Saturn in 2004 and 2007. They measured the ratio of the landslide’s vertical to horizontal motion, and estimated the friction involved. The ratios indicate that the friction was caused by flash heating of the ice until it was slippery enough to slide on, without completely melting.
It could involve a phenomenon known as pre-melting, where only a thin layer of ice crystals melt. Since Iapetus is so cold, ice acts like rock on Earth.
Reference: “Massive ice avalanches on Iapetus mobilized by friction reduction during flash heating” by Kelsi N. Singer, William B. McKinnon, Paul M. Schenk and Jeffery M. Moore, 29 July 2012, Nature Geoscience.