February 9, 2010

Cassini Evidence Suggests Enceladus Harbors Water

Astronomers say it is likely that Saturn's moon Enceladus hides a large body of liquid water just beneath its icy surface, BBC News reported.

More data returned from the Cassini probe, which periodically sweeps past the little moon, has provided even more evidence backing the idea of a sub-surface sea below the moon's surface.

Experts theorize that it is the detection of negatively charged water molecules in the atmosphere of Enceladus. Such ions on Earth are often seen where liquid water is in motion, like waterfalls or crashing ocean waves.

Enceladus may not have any "rollers" but it does have a very active region near its south pole where water vapor and ice particles shoot through cracks in the surface and rise high into the moon's atmosphere.

Andrew Coates from University College London's Mullard Space Science Laboratory said they have seen water molecules that have additional electrons added.

Coates told BBC News there are only two ways they could be added -- from the ambient plasma environment, or from friction as water clusters come out of the jets, like rubbing a balloon and sticking it on the ceiling.

The space probe has already detected sodium in the plumes -- a signature of the dissolved salts you would expect to find in any mass of liquid water that had been in contact with rock deep within the world for a long period.

The Cassini plasma spectrometer (CAPS), which collected the data, was originally flown to acquire information on Saturn's magnetic environment, by measuring the density, flow velocity and temperature of ions and electrons.

However, CAPS ended up sampling jets at Enceladus.

Coates said that while it was no surprise they found water, the short-lived ions are extra evidence for sub-surface water and where there's water, carbon and energy, some of the major ingredients for life are present.

"The surprise for us was to look at the mass of these ions. There were several peaks in the spectrum, and when we analyzed them we saw the effect of water molecules clustering together one after the other."

The measurements were made as the probe plunged through the plumes of Enceladus in a close fly-by in 2008, according to the report published in the journal Icarus.

Cassini's Ion and Neutral Mass Spectrometer (INMS) has already identified positively charged hydrocarbons at Enceladus.

CAPS found not only negatively charged water ions but hints of negatively charged hydrocarbons as well.

However, CAPS has definitely seen negatively charged hydrocarbons on Saturn's largest moon, Titan -- where colossal ions, some measuring more than 13,000 amu (an amu is roughly the mass of a single hydrogen atom) were recorded.

Coates explained that if you have a methane and nitrogen atmosphere and you bombard it with particles from the Saturn's magnetosphere and ultraviolet light from the Sun, you can cook up really large molecules.

"They get bigger as the altitude decreases. They are the source of Titan's haze and also maybe the source of the dunes on the surface as they rain down," he added.

NASA, the ESA, and the Italian Space Agency all developed Cassini as a joint venture for space exploration.


Image Caption: False color Cassini image of jets in the southern hemisphere of Enceladus. Credit: NASA/JPL/Space Science Institute


On the Net: