The ocean inside Titan, the largest moon orbiting Saturn, is probably a "dead sea" just as salty as its Dead Sea equivalent here on Earth and thus unlikely to support any alien life, scientists say.
Using data gathered during 10 years of repeated fly-bys of the moon by NASA's Cassini spacecraft, the researchers determined a subsurface ocean of comparatively high density was necessary to explain Titan's observed gravity.
Extremely salty water full of dissolved salts of sodium, potassium and sulphur could account for such density, they said.
"This is an extremely salty ocean by Earth standards," study lead author Giuseppe Mitri of the University of Nantes in France says. "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."
Titan's salty ocean is covered by an ice shell with thickness that varies in different areas of the moon but is rigid, an indication the salty ocean beneath is slowly crystalizing and itself turning into ice.
That could have implications bearing on the possibility of Titan's ocean being habitable for any kind of life, the researchers said, since the continued freezing would limit any exchange of materials between the icy surface and a slowly freezing ocean below.
Such possible exchanges could help explain another major mystery about Titan, the researchers say: The presence of significant amounts of methane in its atmosphere.
Scientists have detected methane and other hydrocarbon compounds in Titan's atmosphere, but such elements and compounds are destroyed by sunlight in just tens of millions of years, suggesting something has constantly been replenishing methane in the atmosphere throughout the moon's long 4.5 billion year history.
If Titan's ice shell is for the most part rigid, then any outgassing of methane to replenish the moon's atmosphere must be occurring at widely scattered "hot spots," similar to the volcanic hot spot here on Earth that has formed the chain of the Hawaiian Islands over eons.
Broader processes like plate tectonics or convection are unlikely given the overall rigidity of Titan's surface ice shell, the scientists say.
More data will be needed to determine that for sure, they say.
"Our work suggests looking for signs of methane outgassing will be difficult with Cassini, and may require a future mission that can find localized methane sources," study co-author Jonathan Lunine, a Cassini mission scientist with Cornell University says. "As on Mars, this is a challenging task."
