Using telescopes in Hawaii and Australia, Nicholas Schneider and colleagues searched for salts in the plumes themselves. Even from Earth, the signature of sodium should be easy to see, he noted.
"Sodium is an incredibly visible element, the same one we use in streetlights," Schneider said.
But Schneider's team found no sodium in the water-vapor clouds near the moon.
While postberg believes the results of both studies could point to an ocean leaking out into space, Schneider is less certain.
The salts found in icy particles in the E ring are not enough to account for an underground ocean, at least not one near the moon's surface, Schneider said.
Instead he thinks there's a chance the plumes are created by freshwater reservoirs or even tectonic motion moving and warming the surface ice. (Get an overview of plate tectonics.)
"As much as I and many of my colleagues have a wish for there to be an ocean creating these plumes, I think the jury is still out," Schneider said.
Ocean or Puddles?
Astronomer John Spencer, of the Southwest Research Institute in Boulder, Colorado, thinks the discovery of salt in the E ring provides great evidence for liquid water below Enceladus's icy crust.
The water could be in the form of an ocean, said Spencer, who wrote a commentary for Nature discussing the two papers. Or the water could be in under-ice puddles near the moon's surface.
Around the warmer tiger stripes, slightly salty surface ice could be melting, creating puddles that become saltier as some of the liquid evaporates.
"But even if it was a liquid puddle, that's still pretty exciting," he noted. "We haven't found liquid puddles anywhere else [aside from Earth]."
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