Enceladus May Have Saltwater Ocean

Geysers on Enceladus, a moon of Saturn, appear to come from an ocean of saltwater underneath the moon's surface.

In 2005, NASA's Cassini spacecraft discovered jets of water vapor and ice spurting up from fissures, which are known as "tiger stripes", on Enceladus.

Cassini was launched in 1997 and has been in orbit around Saturn since 2004.

The craft examined these geysers again during flybys in 2008 and 2009.

According to a paper by an international team of astronomers, led by Frank Postberg at the University of Heidelberg, which was published in Nature, analysis of the grains expelled from the tiger stripes show that grains far away from the moon are usually small, with a low salt content. However, grains closer to the surface of Enceladus are larger and have a high sodium and potassium content.

According to Postberg, the existence of these larger salt-rich grains indicates that there a reservoir of saltwater under the icy surface of the moon.

Salt is squeezed out of water when it freezes, so if the geysers were derived from the surface ice, they should have very low quantities of salt.

The data suggests there must be an ocean, up to 50 miles (80 kilometers) deep, underneath the surface on Enceladus.

This ocean contains salt compounds that come from rocks, which dissolve in the water as the ocean rushes past them.

The saltwater rises though fractures in the ice, forming water reserves near the surface.

When the outer layer of ice cracks open, the decrease in pressure causes a plume of water vapor and ice to erupt.

Every second, about 400 pounds (200 kilograms) of water vapor and smaller amounts of ice grains are ejected.

Postberg's team has determined that the water reserves must have large surface areas on which evaporation can occur, or they would freeze before they were released into the air.