Cassini Spacecraft Detects Sodium In The Ice In Saturn's Rings

European scientists on the joint NASA/ESA Cassini mission have detected, for the first time, sodium salts in ice grains of Saturn's E-ring, which is primarily replenished by material from the plumes of water vapour and ice grains emitted by Saturn's moon Enceladus. The detection of salty ice indicates that the little moon harbors a reservoir of liquid water, perhaps even an ocean, beneath its surface.

Cassini discovered the water-ice plumes on Enceladus in 2005. These plumes, emitted from fractures near its south pole, expel tiny ice grains and vapour, some of which escape the moon's gravity, replenishing Saturn's outermost ring, the E-ring.

Cassini's Cosmic Dust Analyzer, led by Principal Investigator Ralf Srama, of the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, has examined the composition of these grains and found sodium salt (or table salt) within them.

"We believe that the salty material deep inside Enceladus washed out from rock at the bottom of a liquid layer," said Frank Postberg, Cassini scientist on the Cosmic Dust Analyzer at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Postberg is lead author of a study that appears in the 25 June issue of the journal Nature.

Scientists working on the Cosmic Dust Analyzer conclude that liquid water must be present because it is the only way to dissolve significant amounts of minerals to account for the levels of salt detected. The process of sublimation - the mechanism by which vapour is released directly from solid ice in the crust - cannot account for the presence of salt.

The makeup of the E-ring grains, determined through the chemical analysis of thousands of high-speed particle hits registered by Cassini, provides indirect information about the composition of the plumes and about what lies inside Enceladus. The E-ring particles are almost pure water-ice, but nearly every time the dust analyzer checked for composition, it found at least some sodium within the particles.

"Our measurements imply that besides table salt, the grains also contain carbonates like soda; both components in concentrations that match the predicted composition of an Enceladus ocean," said Postberg. "The carbonates also provide a slightly alkaline pH value. If the liquid source is an ocean, then that, coupled with the heat measured at the surface near the moon's South Pole and the organic compounds found within the plumes, could provide a suitable environment on Enceladus for the formation of life precursors."

FMI: www.nasa.gov