Titan's floating islands: New study unveils porous ice theory

Saturn’s , is a world unlike any other in our solar system. It has a thick orange haze shrouding its surface, dotted with dark organic dunes, and filled with lakes and seas of liquid methane and ethane. But what makes Titan even more intriguing are the mysterious bright spots that appear and disappear on the liquid surfaces, as seen by the mission in 2014.

These spots, dubbed “magic islands,” have puzzled scientists for years. Are they real islands, or just illusions caused by waves or bubbles? A new study published in proposes a novel explanation for the magic islands: they are floating chunks of porous, frozen organic solids. The study, led by planetary scientist Xinting Yu, challenges the previous hypotheses that the islands were either gas bubbles or suspended or floating solids.

Yu was curious about the origin and fate of the organic solids that fall from Titan’s upper atmosphere, which is rich in methane and other carbon based molecules. These molecules can stick together, freeze, and rain down on Titan’s surface, including its liquid bodies. “Would these organic solids sink or float when they reach the lakes?” You wondered.

“I wanted to investigate whether the magic islands could actually be organics floating on the surface, like pumice that can float on water here on Earth before finally sinking.” Yu and her team used models to simulate how the organic solids would behave in Titan’s methane lakes. They found that the lakes were already saturated with organic particles, so the solids would not dissolve.

However, they also found that most of the solids were too dense to float and that the low surface tension of the methane and ethane liquids would make it difficult for them to stay on the surface. The team concluded that the solids could only form the magic islands if they were porous enough to trap air inside them, like Swiss cheese.

The porosity would reduce the density of the solids and slow down the infiltration of the liquid, allowing them to linger on the surface for some time. The team also suggested that the solids could aggregate near the shore and break off into larger pieces, similar to how icebergs calve from glaciers on Earth.

These larger pieces, with the right size and porosity, could then drift away and form the magic islands. The study offers a plausible explanation for the magic islands but also another mystery of Titan: the smoothness of its liquid bodies. The researchers speculated that a thin layer of frozen solids could cover the lakes and seas, reducing the wave activity and creating a calm surface.

Thus, the study reveals how the complex interactions between Titan’s atmosphere, surface, and liquid could produce some of the most fascinating phenomena in our solar system. Study abstract Atmospheric photochemistry on Titan continuously transforms methane and nitrogen gases into various organic compounds.

This study explores the fate of these molecules when they land on Titan's surface. Our analytical exploration reveals that most simple organics found in Titan's atmosphere, including all nitriles, triple bonded hydrocarbons, and benzene, land as solids. Only a few compounds are in the liquid phase, while only ethylene remains gaseous.

For the simple organics that land as solids, we further examine their interactions with Titan's lake liquids. Utilizing principles of buoyancy, we found that flotation can be achieved via porosity induced (25%–60% porosity) or capillary force induced buoyancy for hydrogen cyanide ices on ethane rich lakes.

Otherwise, these ices would sink and become lakebed sediments. By evaluating the timescale of flotation, our findings suggest that porosity induced flotation of millimeter sized and larger sediments is the only plausible mechanism for floating solids to explain the transient “magic islands” phenomena on Titan's lakes..