Mystery of Saturn Moon’s Disappearing Island May Be Due to Ocean Bubbling

March 30, 2016 | Joanne Kennell

Photo credit: NASA

The oceans are fizzy like a bottle of Coca-Cola.

An island, located on Saturn’s moon, Titan, is mysteriously disappearing from view, and scientists are not exactly sure why.

Titan is the only other place in the solar system besides Earth with open bodies of liquid on its surface. However, since the temperature on Titan is a balmy -180 degrees Celsius (-292 degrees Fahrenheit), the liquid is not water. Rather, observations made from NASA’s Cassini probe have confirmed the oceans are liquid hydrocarbons, such as ethane and methane.

Just like our oceans contain dissolved salt, Titan’s hydrocarbon oceans are mixed with nitrogen gas. Michael Malaska of NASA’s Jet Propulsion Laboratory in Pasadena California and his colleagues have discovered that this nitrogen can actually bubble out of the oceans, making them fizzy — like a bottle of Coca-Cola.

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To test this idea, Malaska and his team mixed nitrogen gas with various combinations of methane and ethane at Titan-like temperatures. They found that the amount of nitrogen dissolved in the hydrocarbons decreased as the liquid got warmer. What this means is that, on Titan, any amount of extra sunlight would be enough to release nitrogen trapped in the hydrocarbons.

The amount of dissolved nitrogen also depends on the exact blend of hydrocarbons, but exactly what the bubbles would look like on Titan depends on how rough the bottoms of the lakes are, since a smoother surface has fewer spots where the bubbles can form — known as nucleation sites.

“If there’s a lot of nucleation sites, you’ll get a lot of bubbles,” said Malaska to New Scientist. “If there are only a few, you might get one bubble that becomes really big and pops up.”

Bubbles like this could explain Titan’s disappearing island, a feature in the Ligeia Mare Sea that repeatedly disappears and reappears in radar images taken by Cassini over the past few years.

“You can get a very large amount of bubbles coming out, and if those bubbles happen to have a pattern such that you get a radar signature, you would see the radar footprint we saw for the magic island,” said Malaska to New Scientist. Malaska presented the work at the Lunar and Planetary Science Conference (LPSC) in The Woodlands, Texas, last week.

The results also mean that NASA must think carefully if it goes ahead with a proposed mission to drop a robot submarine on Titan. If Malaska is correct, dropping a robot would be like dunking an Alka-Seltzer in water, producing huge amounts of bubbles.

Current designs for the submarine discussed at LPSC suggest placing scientific instruments at the front and its heat-producing engines at the back, to avoid any interference from the ongoing production of bubbles.

Titan continues to be full of surprises. Malaska told New Scientist, “We used to think of Titan as very Earth-like, but the more we learn about it, we learn it is really weird.”

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