June 22, 2011
Scientists Find Evidence Of Ocean On Enceladus
Scientists say they have found convincing evidence that Saturn's moon Enceladus has a large-scale subterranean saltwater ocean.
The discovery was made using data collected during the Cassini-Huygens mission to Saturn.
The plumes of shooting water vapor and tiny grains of ice into space were originally discovered emanating from Enceladus by the Cassini spacecraft in 2005.
The researchers from the University of Heidelberg and University of Colorado said during three of Cassini's passes through the plume in 2008 and 2009, the Cosmic Dust Analyser (CDA) onboard Cassini measured the composition of ejected plume grains.
The icy particles hit the detector's target at speeds of up to 11 miles per second.
The CDA separated the constituents of the vapor clouds, allowing scientists to analyze them.
The study found the ice grains closer to Enceladus indicate that relatively large, salt-rich grains dominate the surface.
"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," Frank Postberg of the University of Germany, lead author of a study being published in Nature on June 23, said in a statement.
According to the researchers, the salt-rich particles have an "ocean-like" composition that indicates most of the expelled ice from the evaporation of liquid salt water rather than from the icy surface of the moon.
"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.
"The E Ring is made up predominately of such salt-poor grains, although we discovered that 99 percent of the mass of the particles ejected by the plumes was made up of salt-rich grains, which was an unexpected finding," said Kempf. "Since the salt-rich particles were ejected at a lower speed than the salt-poor particles, they fell back onto the moon's icy surface rather than making it to the E Ring."
The researchers believe that a layer of water exists 50 miles beneath the surface crust of Enceladus.
They said about 440 pounds of water vapor is lost every second from the plume, along with smaller amounts of ice grains.
According to the authors, salt in the rock dissolves into the water, which accumulates in a liquid ocean beneath the icy crust.
"Enceladus is a tiny, icy moon located in a region of the outer Solar System where no liquid water was expected to exist because of its large distance from the sun," Nicolas Altobelli, ESA's project scientist for the Cassini-Huygens mission, said in a statement
"This finding is therefore a crucial new piece of evidence showing that environmental conditions favorable to the emergence of life may be sustainable on icy bodies orbiting gas giant planets."
The researchers collaborated with the European Space Agency and NASA for the study.
The Cassini spacecraft is carrying 12 science instruments, including a $12.5 million CU-Boulder ultraviolet imaging spectrograph designed and built by a LASP team led by Professor Larry Esposito.
Image Caption: This image shows icy spray spewing from Saturn's moon, Enceladus. Credit: NASA/JPL/Space Science Institute
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