The strangely unshifting sands and sparkling seas of Saturn’s moon, Titan
In 2005, the Cassini spacecraft launched the Huygens probe on a one-way trip to Saturn’s largest moon, Titan. For over two hours, the probe flew through Titan’s dense atmosphere of nitrogen and methane, finding a landscape of rocky, icy terrain with signs that liquids had once flowed over its surface. Since then, continued study of Titan’s atmosphere and surface has found a variety of weird phenomena, from burping lakes to electrically-charged sand dunes.
Titan’s atmosphere is thicker than Earths, with large amounts of nitrogen acting like a heat shield for the moon’s surface. Rather than capture heat the way carbon dioxide does on Earth, Titan’s atmosphere reflects a lot of sunlight back into space, keeping the surface around -290º Fahrenheit. There is some variation in temperature though thanks to movement of clouds around the moon, which is key to the weird bubbling seen in the lakes of liquid methane, ethane or other organic compounds.
When temperatures drop due to cloud cover and raining methane, the lakes, rivers and small seas, mostly clustered near the poles, can absorb a lot of atmospheric nitrogen. When things clear up, the liquid methane warms enough to shake things up, and the nitrogen molecules congeal into bubbles of gas that rise to the surface, like a giant, stinky soda fizzing up. In some cases the bubbles congeal in huge bubbles that get compared to temporary islands, which then pop like a huge eruption, belching the nitrogen back into the atmosphere.
The drier parts of Titan have their own quirks as well. Sand dunes almost 300 feet high have been found that are somehow shaped in defiance of the prevailing winds. Somehow the sand appears to be shaped by westerly winds, even though they usually blow in from the east. They’re not especially strong winds at the surface, but scientists have been trying to figure out why they weren’t shaping the sand dunes since 2005.
Scientists from Georgia Tech have started looking into whether the issue with the dunes isn’t Titan’s weather, but found in the sand itself. The sand isn’t the silicon dioxide most commonly found on Earth, but is instead likely bits of water ice coated in the various hydrocarbons that make up Titan’s atmosphere, like the aforementioned methane and ethane. While the Huygens probe did gather lots of data for us, it wasn’t ready to answer this question, and so researchers have been experimenting with forms of Titanesque sand here on Earth.
The key to their hypothesis is the alien sand’s electric charge. Putting synthesized sand in a pressurized, rotating cylinder, they looked at how the surface conditions of Titan might cause sand to build up a static charge. They found that their simulated sand did indeed clump thanks to static electricity, not unlike the way a charged balloon can stick to a wall. So smaller winds probably rub the sand together, helping it charge it with electrostatic stickiness. Only larger, less common winds are then strong enough to really blow the dunes down.
Source: NASA/JPL Scientists Think Titan's Towering Dunes Are Made of Unyielding Electric Sand by Peter Dockrill, Science Alert