The particles over the surface of Titan, Saturn’s biggest Moon, might be electrically charged, suggests a new study published in Nature Geoscience. The ‘electric sands’ clump together when blown up by winds, and the dunes can reach great heights.
The non-silicate granules covering the surface of Titan offer a most spectacular scene when prevailing winds (15 kph) blow: they are moved upwards, and begin to hop in a movement pattern called saltation. As they are floating, they collide with each other, an interaction that causes them to become frictionally charged. This makes them adhere to one another, and as they clump together, they resist further movement. They stay thus electrically charged for long stretches of time, from days to months—a sight never seen regarding Earth’s sand dunes.
These findings, however, do not come from first-hand observation. Rather, a team of researchers from the Georgia Institute of Technology conducted experiments that made the case for electrically charged surface particles. They rotated grains of naphthalene and biphenyl, two compounds assumed to exist on Titan, in dry, pure nitrogen, inside a pressure vessel—conditions believed to occur on the moon. This caused the particles to cling together; when their electric properties were measured, they were found to charge well. These results suggest that the grains on the surface of Titan are electrically charged, causing them to adhere.
Study lead author, Josef Dufek, explains that sand castles on Titan would probably last for weeks on end thanks to the electrostatic forces keeping the grains together. The grains can get attached to other hydrocarbons compounds during this period.
“Any spacecraft that lands in regions of granular material on Titan is going to have a tough time staying clean. Think of putting a cat in a box of packing peanuts,” says Dufek.
These findings might help explain a phenomenon on Titan that has otherwise remained unexplained, says co-lead author, Méndez Harper. The moon has sandy dunes towering over around 90 metres on one side in spite of the presence of winds blowing on the other side. The sand dunes might remain bold in the face of prevailing winds because the latter are not strong enough to shape them as the grains stick together due to the electric charges between them.
Why can’t sand castles we build on Earth last for long?! The team repeated the pressure vessel experiment with sand and volcanic ash under Earth-like conditions, and the particles could not cling together; rather, they all came out. Our sand particles do have electric charges when they are in motion, but these are too small to make the grains cohesive. This is why our sand castles need water to form well.
Titan is visually quite like Earth, but, otherwise, it is very much different. Data from Cassini flybys have shown that it has enormous liquid lakes filled, not with water, but with methane and ethane. The pressure on its surface is also higher than ours: standing there would be tantamount to standing (around) 4.5 metres underwater.
“Titan is a strange, electrostatically sticky world,” comments Dufek.