A watery ocean inside Saturn's largest moon, Titan, is as salty as the Dead Sea, scientists believe.
The conclusion is based on data collected during repeated fly-bys of Titan by the American space agency Nasa's Cassini space probe.
Researchers found that the ocean had to have a relatively high density to explain gravity readings recorded by Cassini.
This indicated that the ocean is likely to be a briny mix of water and dissolved salts such as sulphur, sodium and potassium.
The salt content was roughly equal to the saltiest bodies of water on Earth, such as the Dead Sea.
"This is an extremely salty ocean by Earth standards," said lead researcher Dr Giuseppe Mitri, from 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."
The ocean is covered by a stiff icy crust that varies in thickness from place to place, the Cassini data shows.
With such a rigid shell, any out-gassing of methane into the moon's atmosphere was likely to be from scattered "hotspots".
Titan's atmosphere contains about 5% methane, and scientists still cannot explain what geological process is producing it.
The new findings appear in the latest edition of the journal Icarus.