June 24, 2009

Is There An Underground Ocean On Enceladus?

Researchers in Europe released a new report on Wednesday that suggests the geyser seen on the surface of Saturn's moon Enceladus could be fed by a salty ocean underneath the surface.

Writing in the journal Nature, scientists said that the discovery could support theories of the existence of extraterrestrial life.

Scientists first discovered Enceladus' habit of spewing a mix of water vapor, gas and tiny grains of ice into space in 2005 with observations from the Cassini spacecraft.

Enceladus is one of few locations in space where scientists have been able to confirm the presence of water, which is crucial for supporting life.

Frank Postberg and colleagues of the University of Heidelberg and the Max Planck Institute for Nuclear Physics analyzed information documented by the spacecraft's Cosmic Dust Analyzer.

In 2008, Juergen Schmidt of the University of Potsdam, Germany, and Nikolai Brilliantov of the University of Leicester, and colleagues first detailed how water vapor jets are blasted out much faster than the dust particles. Their theory involved the presence of an underwater ocean of liquid water.

For the new study, Postberg's team worked alongside the previous group to discover the "direct experimental evidence for the presence of this ocean."

Based on the presence of sodium salts in the dust being spewed from Enceladus, Postberg and colleagues suggest that an underlying salty ocean could exist.

"The abundance of various salt components in the particles ... exhibit a compelling similarity to the predicted composition of a subsurface Enceladus ocean in contact with its rock core," researchers wrote.

"Individual plume sources stay active for years, implying outflow from a large reservoir."

However, an additional study conducted by Professor Nicholas Schneider of Colorado University, Boulder's Laboratory for Atmospheric and Space Physics, reported that the geysers do not stem from an underground ocean.

"We wondered if there was an ocean underneath that crust and wondered if it is just spraying out through cracks like a geyser boiling away into space," said Schneider.

His team used experiments to determine the relative content of sodium in the water vapor component of the jets spewing from Enceladus. If the jets had originated from an underground salty ocean, scientists would have seen a high sodium content in the water vapor.

Schneider's team used 10-meter Keck 1 telescope and the 4-meter Anglo-Australian telescope to try to detect sodium atoms from the jets. However, they found that few, if any actually existed in the vapor.

"It would have been very exciting to support the geyser hypothesis. But it is not what Mother Nature is telling us," said Schneider in the same issue of Nature as Postberg's study.

"Since our observing team did not find salt in the vapor, our conclusions speak to the conditions of a possible underground ocean on Enceladus," Schneider said.

"Only if the evaporation is more explosive would it contain more salt," said Schneider. "This idea of slow evaporation from a deep cavernous ocean is not the dramatic idea that we imagined before, but it is possible given both our results so far."

He added that all hypotheses about the presence of water on Enceladus must be taken with "a grain of salt."


Image Caption: Water vapor jets spewing from Saturn's icy moon, Enceladus, are not the result of geysers from an underground ocean as envisioned by some planetary scientists but may be caused by water evaporation or ice vaporization, according to a new University of Colorado at Boulder study. Credit: Image courtesy NASA/JPL/Space Science Institute


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