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Astronomy in the News

Mercury Summer 2011 Table of Contents


Enceladus

Plumes spray water ice out from many locations along the famed "tiger stripes" (fissures) near the south pole of Saturn's moon Enceladus. Courtesy NASA / JPL / Space Science Institute.

Evidence Indicates Icy Saturn Moon Hiding Salt

University of Colorado at Boulder

Samples of icy spray shooting from Saturn's moon Enceladus collected during Cassini spacecraft flybys show the strongest evidence yet for the existence of a large-scale, subterranean saltwater ocean. The new discovery was made during the Cassini-Huygens mission to Saturn, a collaboration of NASA, ESA, and the Italian Space Agency. The plumes shooting water vapor and tiny grains of ice into space were originally discovered emanating from Enceladus by the Cassini spacecraft in 2005. The plumes were originating from the so-called "tiger stripe" surface fractures at the moon's south pole and apparently have created the material for the faint E Ring that traces the orbit of Enceladus around Saturn.

During three of Cassini's passes through the plume, the Cosmic Dust Analyser, or CDA, on board measured the composition of freshly ejected plume grains. The icy particles hit the detector's target at speeds of up to 11 miles per second, instantly vaporizing them. The CDA separated the constituents of the resulting vapor clouds, allowing scientists to analyze them.

The study shows the ice grains found further out from Enceladus are relatively small and mostly ice-poor, closely matching the composition of the E Ring. Closer to the moon, however, the Cassini observations indicate that relatively large, salt-rich grains dominate.

"There currently is no plausible way to produce a steady outflow of salt-rich grains from solid ice across all the tiger stripes other than the salt water under Enceladus' icy surface," said Frank Postberg of the University of Germany.

"The study indicates that 'salt-poor' particles are being ejected from the underground ocean through cracks in the moon at a much higher speed than the larger, salt-rich particles," said CU-Boulder faculty member and study co-author Sascha Kempf of the Laboratory for Atmospheric and Space Physics.


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