Titan’s “magic islands” are likely floating patches of porous, frozen organic solids; A new study builds on previous studies that suggested these were gas bubbles. The study was published on: Geophysical Research Letters.

Saturn’s largest moon Titan has a hazy orange atmosphere 50% thicker than Earth’s, rich in methane and other carbon or organic molecules. Its surface is covered with dunes of dark organic matter and seas of liquid methane and ethane. Even more surprising is what appears on radar images as changing bright spots on the sea surface that can last from a few hours to a few weeks or more.

Scientists first noticed these temporary “magic islands” during the Cassini-Huygens mission in 2014 and have been trying to figure out what they were ever since. Previous studies have suggested that these may be ghost islands caused by waves or true islands formed by suspended solids, floating solids or nitrogen bubbles.

Xinting Yu, a planetary scientist and lead author of the new study, wondered whether a closer look at the relationship between Titan’s atmosphere, liquid lakes, and solids settling on the lunar surface could reveal the cause of these mysterious islands.

“I wanted to investigate whether the magic islands were floating organic materials, such as pumice, that could float in water on Earth before eventually sinking,” Yu said.

The wonderful world of organics

Titan’s upper atmosphere is saturated with a variety of organic molecules. Molecules can stick together, freeze, and fall to the moon’s surface; This includes eerily smooth rivers and lakes of liquid methane and ethane with waves only a few millimeters high.

Yu and his team were interested in the fate of these organic clumps after they reached Titan’s hydrocarbon lakes. Will they sink or swim?

To find the answer, the team first investigated whether Titan’s organic matter could dissolve in the moon’s methane lakes. Because the lakes were already saturated with organic particles, the team determined that the falling solids would not dissolve once they reached the liquid.

“For us to see the magical islands, it is not possible for them to float for a second and then sink,” Yu said. “They need to float for a while, but not forever.”

Titan’s lakes and seas consist mostly of methane and ethane; both of these have low surface tension, making it difficult for solids to float. Models suggested that unless the clusters were porous like Swiss cheese, most of the frozen solids were too dense and the surface tension was too low to create Titan’s magical islands.

The researchers found that if ice floes are large enough and the holes are in the right ratio to narrow tubes, liquid methane can leak slowly enough for the ice floes to remain at the surface.

Yu’s simulation suggested that individual clusters were probably too small to float on their own. But if enough clusters coalesce near the coast, larger pieces can break off and blow away, similar to how glaciers grow on Earth. Due to the combination of larger size and correct porosity, these organic glaciers may explain the magic island phenomenon.

In addition to the magical islands, a thin layer of frozen material covering Titan’s seas and lakes could also explain the unusual smoothness of liquid bodies. Therefore, the results of this study may explain two mysteries of Titan.