April 30, 2009

Underground Water Possible On Enceladus

Scientists believe that ice volcanoes observed on Saturn's moon Enceladus may stem from a sea beneath its surface, which could support theories for the existence of extraplanetary life.

Since the Cassini spacecraft arrived on Saturn four years ago, scientists have been trying to determine what is causing Enceladus' volcanoes to spew ice.

"What we have seen over the course of our travels has informed, moved and amazed us," planetary scientist Carolyn Porco, who heads Cassini's imaging team, told Discovery News.

Cassini returned more than 150,000 images of the planet that lies some 1 billion miles away from Earth.

"This debate has been going on for years "” whether there has been liquid water, whether there could be an underground ocean," said Cassini scientist team member Candice Hansen-Koharcheck.

In one step to prove the existence of an underground sea on Enceladus, astronomers used ground-based telescopes to determine the presence of sodium molecules. When none were discovered, many began to deny the possibility of microbial life on the lunar planet.

However, last week Frank Postberg, of the Max Planck Institute for Nuclear Physics told a group of European geoscientists in Vienna that sodium is present, but it is in a form of sodium chloride that cannot be observed by ground-based telescopes.

"This is only possible if the plume source is liquid water that is or has been in contact with the rocky material of Enceladus' core," Postberg and colleagues wrote in the EGU General Assembly's 2009 Geophysical Research Abstracts.

"Suffice it to say the prospects of a sub-surface sea on Enceladus are excellent," Porco told Discovery News in response to Postberg's statement.

In March 2008, the Cassini craft captured new images of Enceladus during a close flyby of nearly 30 miles from the moon's surface.

Scientists previously believed that the moon's internal heat should have been released long ago, but the images spurred the development of new computer models to determine driving forces causing the icy blasts.

Researchers speculated that tidal forces, caused by the gravitational pull of Enceladus' sister moon Dione, could be driving the occurrences.

But while liquid may exist under the moon's surface, the pool may not last forever, scientists told Discovery.

"Our research suggests that you can't have a liquid ocean on a long time scale," said James Roberts with John Hopkins University's Applied Physics Lab, who published his findings last year in the journal Icarus.

"The heat has to be there recently, or there has to be another heating source."


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