Electric grains make Titan a top destination for sand castle builders
It turns out that fizzy lakes may not be the only oddity offered up by Saturn's largest moon. Scientists from the Georgia Institute of Technology say that Titan may also be home to electric sand that rolls around in the wind and forms clumps that cling together for long periods of time. This is not only of interest to pure scientists, but could also make the moon the best place in the Solar System to build sand castles.
Static electricity is a common phenomenon on Earth. At the top end of the scale, we call it lightning and on a more human scale it's used for making balloons stick to the ceiling or getting a shock after walking across a carpet on a dry day. The dry bit is particularly important because this allows a static charge to build up in balloons or unfortunate fingers instead of quickly dissipating away.
It's also the reason the Moon is such an untidy place. It's very dry on the Moon, so static electricity builds up easily and lunar dust clings tenaciously to things, like the spacesuits of the Apollo astronauts, who ended up looking like they'd fallen into a crater full of soot.
This is also the case on Titan, which has a nitrogen/methane atmosphere half again as dense as Earth's, with winds blowing gently at under 5 mph (8 km/h). However, sometimes the winds gust up to 15 mph (24 km/h). This may not seem like much, but in the thicker Titanian atmosphere, it feels more like 60 mph (97 km/h) and these gusts can turn the surface of the moon into a huge electrostatic generator as the non-silicate granules are picked up in the wind and leap about.
According to the Georgia Tech team investigating the phenomenon, these hopping granules pick up an electric charge and, unlike Earthly sand, they clump together until they resemble the packing "peanuts" used to protect items during shipment. These peanuts, in turn, stick to one another or to other hydrocarbons and resist further motion until the charge dissipates over a period of days or months.
One aspect of this clumping is that it changes the amount of friction that the sand can generate, a bit like how wet sand on Earth can be piled at a much steeper angle than dry sand. This helps to explain why images of Titan sent back by NASA's Cassini deep space probe often show dunes almost 300 ft (91 m) tall, yet face in the opposite direction from the prevailing winds that blow from East to West.
The Georgia tech scientists tested their hypothesis by recreating Titanian conditions in a laboratory using a pressure chamber containing nitrogen and methane. Inside this was a smaller cylinder filled with naphthalene and biphenyl, which are believed to be present on Titan. They then rotated the cylinder for 20 minutes and measured the electric charge of grains as the fell out.
When the experiment was conducted using a control of sand and volcanic ash in Earth's atmosphere, nothing clung to the inside of the cylinder, but the Titan cylinder saw between two and five percent sticking to the inside wall.
"If you grabbed piles of grains and built a sand castle on Titan, it would perhaps stay together for weeks due to their electrostatic properties," says Josef Dufek, the study co-leader. "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.
"Titan's extreme physical environment requires scientists to think differently about what we've learned of Earth's granular dynamics. 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."
The research was published in Nature Geoscience.
Source: Georgia Tech