Data from NASA’s Cassini spacecraft reveal that the ocean inside Saturn’s largest moon, Titan, could be as salty as the Dead Sea -- the super-saline lake at the lowest spot on Earth. The findings were published in Icarus this week.
Previous data have indicated that Titan’s icy shell -- which overlies an ocean -- is rigid and currently in the process of freezing solid. During its repeated flybys of Titan over the last decade, Cassini has collected a multitude of gravity and topography data, and scientists have now used them to create a model structure of the giant moon.
After analyzing the gravity anomalies seen in the new data, a team led by Giuseppe Mitri of the University of Nantes, France, determined that the underlying ocean must have a relatively high density. That means Titan’s ocean is likely an extremely briny mix of water and dissolved salts, likely composed of sulfur, sodium, and potassium. Its density would give the ocean a salt content like that of the saltiest bodies of water on our planet.
"This is an extremely salty ocean by Earth standards," Mitri says in a news release. "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." The freezing process would also limit the exchange of materials between the surface and the ocean.
Additionally, they found that the thickness of the ice crust varies slightly from place to place around the moon. This further confirms that the outer shell is stiff, which would be the case if the ocean was slowly crystalizing and turning to ice. Otherwise, the shape of the moon would even itself out over time, like hot wax.
Another consequence of a rigid ice shell is that any outgassing of methane into the atmosphere must happen at scattered hot spots, like the ones that gave rise to the Hawaiian Islands. At the moment, Titan's atmosphere contains about five percent methane.