saturn’s moon Bubbling ocean on Saturn’s moon could explain vanishing island

[Reefa]

Lakes like a fizzy drink

The oceans and lakes on Saturn’s moon Titan might be fizzy – a suggestion that could explain a mysterious disappearing island recently seen on the surface.

Titan is the only place in the solar system besides Earth with open bodies of liquid on its surface. But since the temperature is a frigid -180°C, we’re not talking water. Instead, observations from NASA’s Cassini probe have confirmed the oceans are liquid hydrocarbons, like ethane and methane.

And like our oceans contain dissolved salt, Titan’s hydrocarbons are mixed in with nitrogen gas. Imagine Earth’s seas were made of Coca-Cola, and you’re close to the scene on Titan.

Now Michael Malaska of NASA’s Jet Propulsion Laboratory in Pasadena, California, and his colleagues have discovered that the nitrogen can bubble out of the ocean.

Bubbling away

In the lab, his team mixed nitrogen gas with various combinations of ethane and methane at Titan-like temperatures. They found that the amount of nitrogen that dissolved in the hydrocarbons decreased as the liquid got warmer.

On Titan, this would mean that a small amount of extra sunlight would be enough to unlock some of the nitrogen found in the liquid hydrocarbons. Their experiment shows that heating a cup of Titan-like liquid by 1°C would release 2.5 times the volume in nitrogen.

The amount of dissolved nitrogen also depends on the exact blend of hydrocarbons. The team’s results show that if a methane-nitrogen mix rained down on a pure ethane lake, as much as 15 times the volume of nitrogen would be released, potentially making for some very big bubbles. Malaska presented the work at the Lunar and Planetary Science Conference (LPSC) in The Woodlands, Texas, last week.

Exactly what those bubbles would look like on Titan depends on how rough the bottoms of the lakes are, since a smoother surface has fewer spots where bubbles can form, also known as nucleation sites. “If there’s a lot of nucleation sites, you’ll get a lot of bubbles,” says Malaska. “If there are only a few, you might get one bubble that becomes really big and pops up.”

Vanishing island

Such bubbles could explain Titan’s “magic island”, a feature in the Ligeia Mare sea that has repeatedly appeared and disappeared 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,” says Malaska.

They also mean NASA will need to think carefully if it goes ahead with a proposed mission to drop a robot submarine on Titan. If Malaska’s prediction is correct, such a daring manoeuvre would be like dunking an Alka-Seltzer in water, producing a huge amount of bubbles.

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

It just goes to show how much these alien worlds can surprise us, says Malaska. “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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