Titan’s ocean as salty as Dead Sea

NASA scientists have firm evidence that the ocean inside Titan, Saturn’s largest moon, might be as salty as the Dead Sea on Earth. Over the last decade, the Space Agency’s Cassini mission has been collecting gravity and topography data during repeated flybys. From this they have developed a model which has resulted in an improved understanding of the structure of Titan’s outer ice shell. “Titan continues to prove itself as an endlessly fascinating world, and with our long-lived Cassini spacecraft, we’re unlocking new mysteries as fast as we can solve old ones,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory. The team found a relatively high density was required for the ocean to help explain the gravity data, indicating the ocean is probably an extremely salty brine mixed with dissolved salts likely to be composed of sulphur, sodium and potassium. The density indicated for this brine would mean Titan’s ocean has a salt content roughly equal to the saltiest sea on Earth. “This is an extremely salty ocean by Earth standards,” said Giuseppe Mitri from the University of Nantes, and lead author of the study. “Knowing this may change the way we view this ocean as a possible abode for present-day life, but conditions light have been very different there in the past.” Additional findings support previous indications that the moon’s icy shell is rigid and in the process of freezing solid. The thickness of the crust also varies from place to place, which researchers said can be explained if the moon’s outer shell were stiff – as would be the case if it were slowly crystallising and turning to ice. As a consequence, any outgassing of methane into the moon’s atmosphere must happen at scattered ‘hot spots’. How methane appeared in the atmosphere has long been of interest to scientists, as molecules of this gas are broken apart by sunlight. The atmosphere currently contains about 5% methane, which means some process must be replenishing the gas. “Our work suggests looking for signs of methane outgassing will be difficult with Cassini and may require a future mission that can find localised methane sources,” said Jonathan Lunine from Cornell University. “As on Mars, this is a challenging task.”