50 percent of plume shooting out of geysers on Enceladus could be ice

December 21st, 2009 - 1:11 pm ICT by ANI  

London, December 21 (ANI): In a new research, a scientist has revealed that as much as 50 percent of the plume shooting out of geysers on Saturn’s moon Enceladus could be ice.

According to a report in Nature News, the research was led by Andrew Ingersoll, a planetary scientist from California Institute of Technology in Pasadena.

Previously, scientists had thought that only 10-20 percent of the plume was made up of ice, with the rest being water vapour.

Ingersoll based his estimate on a series of photos of Enceladus taken in 2006 by the Cassini spacecraft.

That was a “very special time,” he said, when two important events occurred simultaneously.

Enceladus was perfectly backlit by the Sun, allowing ice particles in its geyser plumes to be easily observed; and at the same time, Cassini was in Saturn’s shadow.

“That allowed us to look back toward the Sun without blinding the instruments,” Ingersoll said.

The photos showed Enceladus at different points in its orbit in three wavelength bands - ultraviolet, visible and near-infrared.

In combination, the images allowed Ingersoll’s team to determine the size of the plume’s ice particles as well as their concentration.

The team then calculated how fast new ice particles had to blast out of the moon’s geysers for the plume to contain the amount of ice seen in the images.

They found that Enceladus must be emitting at least 200 kilograms of ice per second - almost identical to the amount of water vapour other measurements had determined it to be emitting.

According to Ingersoll, one way to get more ice is if the geyser chambers contain water.

“When a crack opens up, the water is exposed to the vacuum of space and starts to boil,” he said.

But much of the steam immediately freezes, “and you get a large fraction of solids” in the plume,” he added.

Susan Kieffer, a planetary scientist from the University of Illinois at Urbana-Champaign, takes into account clathrates, which are molecular-sized cages of a compound that can contain many other molecules.

The clathrates that feed Enceladus’s plumes could encage the numerous other gases that make up about 10 percent of the plume.

When the clathrates break down, according to Kieffer, they would release not just water vapour, but also ice particles into the plume - likely enough to account for Ingersoll’s data.

“We can make a lot of ice in our model,” she said. (ANI)

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