Titan, Saturn’s most prominent moon, is a thoroughly strange place. The only satellite known to have a thick atmosphere, it also happens to feature a complex climate, including rivers, lakes, storms, ponds, pools and seas – they’re just made of methane and ethane, not water.
It also features some rather strange sand dunes, which are often 100 meters (roughly 300 feet) high. On Earth, sand dunes form when wind blows sand across a desert or beach and it manages to pile up. With few exceptions, the sand dunes always point in the direction of the prevailing wind.
On Titan, they often do precisely the opposite, and now researchers have finally figured out why: static electricity, or "electrostatics," is binding them together.
If the wind is blowing in a northerly direction, you’d expect the sand dune to be tipping over towards the north, but on Titan, it would frequently be pointing towards the south. This is weird, but it suggests that the sand there isn’t quite like the type we find on our own planet.
A team of scientists from Georgia Tech, after engaging in a few thought experiments, realized that Titan’s sand could be composed of particles that exhibit a very strong electrostatic force – the same force that gives you shocks when you touch a metal object in a very dry environment, and the very same that produces volcanic lightning.
Electrostatics refers to stationary or slow-moving electrical charges. The surfaces of certain materials are prone to accumulating electric charge, which attracts objects or particles that have the exact opposite electric charge. This is known as electrostatic attraction, and it is magnitudes stronger than the force of gravity.
The electric sand dunes of Titan. NASA Jet Propulsion Laboratory via YouTube
The team of geophysicists pondering on Titan’s wacky dunes suspected that the sand over there was particularly vulnerable to electrostatic charge accumulation. If enough of this sand rubbed together, it would generate so much charge that it would refuse to change shape even in the face of strong prevailing winds.
In order to test this, the team grabbed two specific compounds of solid hydrocarbons thought to exist on Titan, plonked them in various pressurized containers full of Titan’s nitrogen-rich atmosphere, and spun them around to simulate the flow of wind.
After the spinning ceased, the team found that up to 5 percent of the hydrocarbon sand formed little dunes that stuck to the container. The same couldn’t be said for tests involving regular silica sand or even volcanic ash, which suggests that you get electrostatic sand dunes on Titan, but not Earth.
“We conclude that, unlike other Solar System bodies, nanometre-scale electrostatic processes may shape the geomorphological features of Titan across the moon’s surface,” the team wrote in their Nature Geoscience study.