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SATURN'S MOON

The electric sands of Titan

Experiments suggest the particles that cover the surface of Saturn's largest moon are electrically charged

Experiments led by researchers at the Georgia Institute of Technology suggest the particles that cover the surface of Saturn's largest moon, Titan, are "electrically charged." When the wind blows hard enough Titan's non-silicate granules get kicked up and start to hop in a motion referred to as saltation.


As they collide, they become frictionally charged, and clump together in a way not observed for sand dune grains on Earth -- they become resistant to further motion. They maintain that charge for days or months at a time and attach to other hydrocarbon substances. The findings have just been published in the journal Nature Geoscience.


The electrification findings may help explain an odd phenomenon. Prevailing winds on Titan blow from east to west across the moon's surface, but sandy dunes  seem to form in the opposite direction. These electrostatic forces increase frictional thresholds, this makes the grains so sticky and cohesive that only heavy winds can move them. The prevailing winds aren't strong enough to shape the dunes.


To test particle flow under Titan-like conditions, the researchers built a small experiment in a modified pressure vessel in their Georgia Tech lab. They inserted grains of naphthalene and biphenyl -- two toxic, carbon and hydrogen bearing compounds believed to exist on Titan's surface -- into a small cylinder. Then they rotated the tube for 20 minutes in a dry, pure nitrogen environment (Titan's atmosphere is composed of 98 percent nitrogen). Afterwards, they measured the electric properties of each grain as it tumbled out of the tube.

 

All of the particles charged well, and about 2 to 5 percent didn't come out of the tumbler, they clung to the inside and stuck together. When we did the same experiment with sand and volcanic ash using Earth-like conditions, all of it came out. Nothing stuck.

Earth sand does pick up electrical charge when it's moved, but the charges are smaller and dissipate quickly. That's one reason why you need water to keep sand together when building a sand castle. Not so with Titan.

 

Visually, Titan is the object in the solar system most like Earth. Data gathered from multiple flybys by Cassini since 2005 have revealed large liquid lakes at the poles, as well as mountains, rivers and potentially volcanoes. However, instead of water-filled oceans and seas, they're composed of methane and ethane and are replenished by precipitation from hydrocarbon-filled clouds. Titan's surface pressure is a bit higher than our planet -- standing on the moon would feel similar to standing 15 feet underwater here on Earth.


"Titan's extreme physical environment requires scientists to think differently about what we've learned of Earth's granular dynamics," said Dufek, co-author of the sttudy - landforms are influenced by forces that aren't intuitive to us because those forces aren't so important on Earth. Titan is a strange, electrostatically sticky world."