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Saturn moon harbours hidden ocean

saturn's moon

Saturn's moon show's signs of a salty ocean(Source: NASA/JPL)

Huge geysers on Saturn's moon Enceladus may be fed by a salty sea below its surface, according to a European study.

Researchers detected salt particles in the volcanic vapour-and-ice jets that shoot hundreds of kilometres into space, the strongest evidence to date of a liquid ocean under the moon's icy crust.

The study, published in the journal Nature, boosts the odds of extraterrestrial life in our solar system.

Scientists already knew that tiny Enceladus, only 500 kilometres across, had two of the three essential ingredients for life.

One is an energy source produced by tidal warming, which may be driven by the shifting gravitational tug of its parent planet during the moon's lopsided orbit.

Since 2004, the Cassini spacecraft circling Saturn has also found a potentially life-sustaining mix of organic chemicals in Enceladus' plumes.

The particles are ejected from a quartet of 120 kilometre long fractures, known as 'tiger stripes'.

That left the third critical ingredient: liquid water.

Deep ocean

Since their discovery in 2005, the giant geysers have fuelled intense speculation on the presence of a subterranean ocean. The new discovery goes a long way toward resolving one of the most hotly debated topics in planetary science.


Their results show that ice grains in the Enceladus plumes contain substantial quantities of sodium salts. This suggests that the moon's hidden sea - if there is one - could be as salty as Earth's oceans.



According to John Spencer of the Southwest Research Institute in Colorado, sodium is a good telltale tracer of possible liquid water for two reasons.

It is highly soluble, he says, so any Enceladan water that has prolonged contact with the moon's silicate core should be rich is sodium salts, like Earth's oceans.

Sodium also scatters sunlight efficiently in the orange-yellow range of the spectrum, making it easy to detect even in minute quantities.

Earth observations

In a second study, also published in Nature, a team led by Nicholas Schneider of Colorado University were unable to detect salts in Enceladus' plumes, using spectrographs on Earth-bound telescopes.

But Spencer says when combined with the Cassini data the Earth-based observations, which seem to challenge Postberg's findings, provide additional evidence to support the deep ocean theory.

The research from Colorado shows the plumes could not have been formed by boiling salty water spewing directly out of Enceladus' tiger stripes, otherwise the sodium would be so abundant as to be observable from Earth.

Instead, the plumes could come from salty water distilling into fresh water vapours, not through evaporation as happens over Earth's oceans, but in pressurised chambers under the moon's surface.

Cassini is scheduled to make four additional up-close fly-bys of Enceladus before mid-2010, and another dozen in the next five years if its mission is extended.

Tags: astronomy-space, chemistry, geology