Saturn's Moon Titan Has Surprisingly Salty Oceans Lurking Under Its Surface

With every new discovery, Saturn’s moon Titan gets more compelling. The latest data from NASA’s Cassini mission has confirmed that not only is there a saltwater ocean beneath the moon’s surface, it might be an ocean as salty as the Earth’s own Dead Sea.

Scientists have inferred that Titan’s subsurface ocean is an extremely salty from gravity and topography data gathered during the last decade. The gravity data told scientists that the subsurface ocean had to have a high density, which means it would have to have some element present in the water.

The likeliest candidates are sulfur, sodium, and potassium, all of which could easily be dissolved in water in the concentrations needed to explain the gravity data. Those concentrations that would make for a very briny ocean.

"This is an extremely salty ocean by Earth standards," said Giuseppe Mitri of the University of Nantes in France. "Knowing this may change the way we view this ocean as a possible abode for present-day life, but conditions might have been very different there in the past.”

An extremely salty subsurface ocean helps explain other observed features of Titan as well, like the thickness of the moon’s crust. The icy surface layer appears to vary in thickness. If it turns out that this outer shell is stiff, it might be a result of the salty subsurface ocean slowly freezing and crystallizing, creating an uneven layer of saltwater ice. It’s the best explanation; otherwise the surface material would freeze regularly, turning the moon into a smooth and even sphere over time.

And of course, a subsurface ocean as salty as the Dead Sea will change the way scientists study the Saturnian moon. A slow freezing process of a salty ocean, and even the salinity of the ocean itself, would limit any exchange of materials between the ocean and the surface, possibly affecting what (if any) living beings that may have lived beneath the icy layer.

The salty subsurface ocean also has implications for one of Titan’s biggest mysteries: the presence of methane in the moon’s atmosphere. Scientists have known for a long time that Titan’s atmosphere has high levels of methane, ethane, acetylene, and a host of other hydrocarbon compounds.

What’s surprising is the high level of methane because sunlight irreversibly destroys this element after tens of millions of years, something has been replenishing Titan’s methane stores during its 4.5 billion years. Scientists are now considering whether outgassing of methane into Titan's atmosphere happened irregularly at certain “hot spots," like the spot on Earth that gave rise to the Hawaiian Islands, rather than a broader, more regular process like convection or movements of plate tectonics.

"Titan continues to prove itself as an endlessly fascinating world," said Linda Spilker, a Cassini project scientist at NASA's Jet Propulsion Laboratory. "With our long-lived Cassini spacecraft, we’re unlocking new mysteries as fast as we solve old ones.”

Between the mysterious levels methane in the atmosphere and a possible subsurface Dead Sea, we really need a dedicated mission to Titan to see what’s going on.