Back in 2013, a bright, mysterious feature on Saturn's moon Titan suddenly appeared in images taken by the Cassini mission's radar instrument. The strange anomaly, not seen in previous images, inexplicably emerged in Ligeia Mare, the second-largest of Titan's seas, located near its north pole.
During a follow-up flyby just days later, the feature - informally dubbed a "magic island" - had vanished. And then two similar anomalies were spotted the following year.
Scientists had a few possible explanations for the phenomenon, but a new study points to a theory that may prove to be the most likely reason: Titan's seas are bubbling with nitrogen, creating island-like features.
The frozen moon's seas aren't made of water. Titan is so cold, averaging −290 °F (−179 °C), that it could only have seas of liquid hydrocarbons like methane and ethane. The combined Cassini and Huygens missions determined that cold liquid methane rains from the skies on Titan and collects in rivers, lakes, and seas.
But how might so-called "islands" suddenly appear in such an environment? A recent experiment by scientists at the Jet Propulsion Laboratory simulated the conditions on Titan, and it showed that just slight changes in temperature, air pressure, or composition can cause the nitrogen to rapidly separate out of a solution, just like the bubbling fizz when a bottle of champagne or soda is opened.
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"Our experiments showed that when methane-rich liquids mix with ethane-rich ones - for example from a heavy rain, or when runoff from a methane river mixes into an ethane-rich lake - the nitrogen is less able to stay in solution," Michael Malaska of JPL, who led the study, said in a press statement.
"The basic idea is that lots of bubbles (or other phenomena) would give the same type of signal as solid land," Malaska added in an email to Seeker. "The radar would bounce off the bubbles and give a similar backscatter signature."