The icy, geyser-like plumes spewing from Saturn's moon Enceladus are sprinkling the planet's famous rings with sodium salts, a new study says.
The finding may mean that the moon, which is completely encrusted with ice, hides a liquid ocean deep beneath its surface.
Images from NASA's Cassini spacecraft first revealed the watery plumes on Enceladus in 2005.
The dramatic discharges shoot thousands of kilometers into space from relatively warm "tiger stripe" fissures near the moon's south pole.
Many astronomers think the geysers created and continue to feed the so-called E ring, Saturn's outermost ring.
New data from Cassini offer evidence of sodium salts in the icy particles of the E ring, which suggests the salts came from Enceladus's plumes.
"It's really hard to explain [salt in the E ring], other than [the theory] that there is a saltwater reservoir feeding the plumes. That's by far the most plausible explanation," said study co-author Frank Postberg, of the Max Planck Institute for Nuclear Physics in Heidelberg, Germany.
In a paper appearing in this week's issue of the journal Nature, Postberg suggests that water exists in deep caverns under the moon's ice.
Salts are washed into the water from rocks on the moon's subterranean seafloor, in a process similar to that seen in Earth's oceans, Postberg thinks.
As the water slowly evaporates, most of the salt gets left behind. But some slightly salty bubbles of gas get propelled into space along the fissures, where they immediately freeze and form part of the massive plumes.
"Jury's Still Out"
A separate study, also published in Nature, may quash the theory of an ocean below Enceladus's surface.
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