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Fizzy lakes for Saturn’s moon Titan?

Bright features – informally known as “magic islands” – seem to appear and disappear in a Titan sea. A new study shows that bubbles could, potentially, be the cause.

No, the video above isn’t from Titan. But it’s a good representation of what scientists now believe might be happening on this largest moon of the ringed planet Saturn. Earth isn’t the only world in our solar system known to have water, but, in Titan’s case, the lakes and seas on its surface don’t contain water. Instead, they have a mixture of liquid methane and ethane. Results from a recent NASA-funded study shows it’s possible that Titan’s hydrocarbon lakes and seas might occasionally erupt with dramatic patches of bubbles. NASA reported on this study on March 15, 2017, saying:

For the study, researchers at NASA’s Jet Propulsion Laboratory in Pasadena, California, simulated the frigid surface conditions on Titan, finding that significant amounts of nitrogen can be dissolved in the extremely cold liquid methane that rains from the skies and collects in rivers, lakes and seas. They demonstrated that slight changes in temperature, air pressure or composition can cause the nitrogen to rapidly separate out of solution, like the fizz that results when opening a bottle of carbonated soda.

NASA said its Cassini spacecraft – which has been orbiting Saturn since 2004, but whose mission will end this year – has found that the composition of Titan’s lakes and seas varies from place to place. Some Titan reservoirs are richer in ethane than methane. Planetary scientist Michael Malaska of JPL (@mike_malaska on Twitter) who led the study, explained:

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.

The result, NASA said, may be:

… bubbles. Lots of bubbles.

The notion of nitrogen bubbles creating fizzy patches on Titan’s lakes and seas is relevant to an unsolved mystery on Titan, what scientists call this moon’s magic islands. During several flybys, Cassini’s radar has revealed small areas on the seas that appeared and disappeared, and then (in at least one case) reappeared. Researchers proposed several potential explanations for what could be creating these island-like features, including the idea of fields of bubbles.

The new study – published in the peer-reviewed journal Icarus – provides details about the mechanism that could be forming bubbles. Jason Hofgartner of JPL, who serves as a co-investigator on Cassini’s radar team and was a co-author of the study, said:

Thanks to this work on nitrogen’s solubility, we’re now confident that bubbles could indeed form in the seas, and in fact may be more abundant than we’d expected.

These Cassini spacecraft images show the evolution of a transient feature in a large hydrocarbon sea on Titan, which scientists call Ligeia Mare. Analysis by Cassini scientists indicates that the bright features, informally known as the “magic island,” are a phenomenon that changes over time. The scientists think the brightening is due to either waves, solids at or beneath the surface, or bubbles. Read more about this image.

If the release of bubbles is causing the effect of the magic island, then it’s possible that release can also occur when Titan’s methane seas warm slightly during the moon’s changing seasons.

NASA also said that a fizzy liquid on Titan might cause problems, potentially, for any future robotic probes sent to float on or swim through Titan’s seas:

Excess heat emanating from a probe might cause bubbles to form around its structures — for example, propellers used for propulsion — making it difficult to steer or keep the probe stable.

As it sped away from a relatively distant encounter with Titan on February 17, 2017, NASA’s Cassini spacecraft captured this mosaic view of the moon’s northern lakes and seas. Cassini’s viewing angle over Kraken Mare and Ligeia Mare was better during this flyby than previous encounters, providing increased contrast for viewing these seas. Read more about this image.

Time is running out for the aging Cassini spacecraft, whose mission is scheduld to end this September. Cassini will make its final close flyby of Titan — its 127th targeted encounter — on April 22. NASA said:

During the flyby, Cassini will sweep its radar beam over Titan’s northern seas one final time. The radar team designed the upcoming observation so that, if magic island features are present this time, their brightness may be useful for distinguishing between bubbles, waves and floating or suspended solids.

Read more via NASA JPL

Bottom line: The liquid ethane and methane lakes and seas on Titan might be fizzy, according to a new study.

Deborah Byrd