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."