Saturn moon Iapetus' huge landslides stir intrigue
Published: 29th Jul 2012 22:01:48
Saturn's moon Iapetus frequently plays host to a huge type of landslide or avalanche that is rare elsewhere in the Solar System, scientists report.
Sturzstroms or "long-runout landslides" move faster and farther than geological models predict they should.
They have been seen on Earth and Mars, but there is debate about their causes.
Now, images from the Cassini space mission, reported in Nature Geoscience, suggest that heating of icy surfaces helps the landslides keep going.
On Earth, landslides typically travel a horizontal distance that is less than twice the distance that the material has fallen.
Long-runout landslides, by contrast, can travel as much as 30 times the vertical falling distance.
A great many mechanisms have been proposed to explain this phenomenon, ranging from simple sliding on ice to the sound waves from the slide making rock and debris behave more like a fluid.
But there is little consensus on which of these theories, if any, is correct.
Now, Kelsi Singer of Washington University in St Louis, US, and colleagues report that the geography of Iapetus is a unique setting to test these theories.
"The landslides on Iapetus are a planet-scale experiment that we cannot do in a laboratory or observe on Earth," Ms Singer said.
"They give us examples of giant landslides in ice, instead of rock, with a different gravity, and no atmosphere. So any theory of long-runout landslides on Earth must also work for avalanches on Iapetus."
Iapetus is a geologically interesting place to look; it is a squashed sphere, fatter at its equator than its poles, and is mostly encircled by a ridge that reaches peaks some 20km high.
It also has a number of giant impact craters reaching depths of 25km.
The icy satellite has more giant landslides than any Solar System body other than Mars. The reason, says Prof William McKinnon, also from Washington University, is Iapetus' spectacular topography.
"Not only is the moon out-of-round, but the giant impact basins are very deep, and there's this great mountain ridge that's 20km (12 miles) high, far higher than Mount Everest," he explained.
"So there's a lot of topography and it's just sitting around, and then, from time to time, it gives way."
Ms Singer was looking for stress fractures in the moon's ice, but instead found evidence of 30 massive landslides - 17 along crater walls and 13 along the giant equatorial ridge.
Analysis of the images from these events suggests that the "coefficient of friction" - a measure of how much the slip-sliding of material in a landslide tends to slow it down - on Iapetus is far lower than expected for ice.
It appears that this faster-moving ice seen on Iapetus has a lower friction coefficient than that of slow-moving ice measured in Earth-bound laboratories.
The team suggests that the tiny contact points between bits of ice debris in such a landslide may heat up considerably, melting it and forming a more fluid - and thus less friction-limited - mass of material.
They suggest that physicists here on Earth test the idea in the laboratory, giving insight not only into what is happening on Iapetus, but closer to home as well.
At 01:58:33 in HeadlinesChester Zoo was the brainchild of a shopkeeper who started it in his back garden. It meant a remarkable childhood for his daughter, writes Ellen Tsang.
At 01:53:08 in BusinessUS auditor Arthur Andersen is having its name resurrected more than a decade after it collapsed because of the Enron accounting scandal.
At 01:45:05 in Entertainment
At 01:39:15 in HeadlinesPatients in Kenya may soon start receiving live maggots as a treatment after promising results from a pilot study using the age-old practice.
At 01:29:26 in WorldThe owners of one the most infamous buildings in Paris have been ordered to put back a commemorative plaque recalling the role of the "French Gestapo" in World War Two.
At 01:24:54 in EnglandA £7m claim has been launched against two firms involved in the design and building of an "eco-school" that closed after it developed leaks.
At 01:24:42 in WorldThe Ukraine conflict has pushed Nato-Russia relations to a new low, and there are fears that the old Cold War suspicions and hostility are back.
At 01:23:52 in HealthAll diets - from Atkins to Weight Watchers - have similar results and people should simply pick the one they find easiest, say researchers.
At 01:17:33 in HealthSurplus NHS land should be used to build dedicated housing for older people, a former care minister says.
At 01:12:46 in EnglandA school aimed at pupils who want to work in the space industry is due to open its doors in Oxfordshire.
Harvard CitationBBC News, 2012. Saturn moon Iapetus' huge landslides stir intrigue [Online] (Updated 29th Jul 2012)
Available at: http://www.ukwirednews.com/news/1443362/Saturn-moon-Iapetus-huge-landslides-stir-intrigue [Accessed 3rd Sep 2014]
News In Other Categories
You may not realise it, but every time you open up your laptop or switch on your phone, you are at the heart of one of the greatest battles now taking place in our midst - what shape will the internet take in the future, and what role will anonymity play in deciding it?
US captain Tom Watson has named Keegan Bradley, Hunter Mahan and Webb Simpson as his three wildcard picks for the Ryder Cup at Gleneagles this month.
There will be no prosecutions over complaints about the performance of a folk band at the Ardoyne Fleadh last month.
All diets - from Atkins to Weight Watchers - have similar results and people should simply pick the one they find easiest, say researchers.
For the past three or four months or so, the referendum race has looked as though it was stalled.
A £7m claim has been launched against two firms involved in the design and building of an "eco-school" that closed after it developed leaks.