In the summer of 2013, Jason Hofgartner and his professors at Cornell University were looking at radar images of Titan, Saturn’s largest moon, when they noticed something strange. There were bright spots inside Ligeia Mare, a large lake in the moon’s northern region, that had never shown up in data before. By the start of 2015, the features had vanished again.
The astronomers dubbed them “magic islands” because of their shape and disappearing act. Nearly three years later, scientists still don’t know what they are or what’s causing them, but they’re days away from getting one last shot to find out.
On Saturday, as Cassini begins its slow descent into Saturn’s atmosphere for the end of its mission, the spacecraft will make one final flyby of Titan. Cassini’s imaging instruments will target Ligeia Mare at a certain angle that will magnify the brightness of these mystery features, if they still exist, and make them more visible. The data that reaches Earth a few days later could help crack the case.
“If anyone’s going to solve it, it’s likely to be this upcoming Cassini observation,” said Hofgartner, a member of Cassini’s radar analysis team.
Hofgartner and his fellow Cornell researchers say there are three potential explanations for “magic islands,” which measure about 10 kilometers (six miles) across. The spots could be some kind of solid suspended in Ligeia Mare, which is a body of liquid mostly made of methane and larger than Lake Superior. They could be bubbles, brought to the surfaces by interactions between methane, ethane, and nitrogen. Or, as Hofgartner suspects, the islands could actually be waves, pushed into existence by wind just like on Earth.