It’s all but official. New data released from the Cassini spacecraft has confirmed that Enceladus, one of the moons of Saturn, has liquid water – as a sea – underneath its exterior layer of ice. The idea of Enceladus having large bodies of liquid water is not new but thanks to Cassini, the evidence is mounting that Enceladus should join Europa (a moon of Jupiter), Titan (another moon of Saturn), and Mars as the most likely places in our solar system to have some kind of life.

Water is the key. Wherever there is liquid water, there is a possibility that organic compounds can find a way to combine into living material. It’s happened before (on Earth, of course) and the odds are fair that it could happen elsewhere in the solar system.

Enceladus, the sixth largest moon of Saturn (about 500 km in diameter, one-seventh the size of Earth’s Moon, not very big) was until the Cassini probe’s flybys considered mostly a ball of ice. Then in 2005 Cassini recorded something unexpected, plumes or jets of what appeared to be water rising into the high atmosphere of Enceladus. This was occurring in the south polar region of the moon, in an area already noted for having peculiar striations in ice (called ‘tiger stripes’).

Credit: NASA

Other moons, notably Io in the Jupiter system, are known to be affected by the tidal pull of their nearby giant planet. This tidal pull produces movement in the rock and materials of the moons, which in turn creates stresses and heat. On Io it produces volcanic eruptions, mostly of sulfur. On Enceladus it apparently contributes to geysers mostly of water. That Enceladus has a rocky core is also a product of Cassini instruments. It is now believed that though small, Enceladus has both tidal heating and heating from decay of radioactive material, which together have created enough heat to either melt the core or produce sustainable pockets of molten rock (magma) in the core or mantle. It is this heat which is responsible for the water jets and the presumed seas (or large chambers) of water. This is certainly in the case of the area near the south pole. Whether it is also true for all of Enceladus is unknown.

The composition of the geysers, or jets that send a plume 500 kilometers from the surface, has now been analyzed at close range from the Cassini close flyby of November 2009. The most important point is the discovery of negatively charged water ions, which are typical of water that has been churned as in ocean waves. Another point, observed earlier, was that the jets contain a surprisingly high concentration of dissolved salts, as would be expected from underlying water (seas) that contact core rocky material. There are also traces of organic compounds, including propane, ethane, acetylene and ammonia. While not unusual in water-ice space objects, the presence of organic material (remember, this does not mean that life produced it) does indicate that some of the known compounds used by living things are present on Enceladus.

Putting all the evidence together: It appears that Enceladus has large bodies of liquid water, probably seas. This water is heated, probably on a continuous basis in much the same way the as the volcanic vents in Earth’s oceans. There are organic materials present in the water, as are charged ions – both conditions usually required for the emergence of life. Conclusive evidence for life will probably have to wait for direct contact with Enceladus, probably by landing a robotic probe. That’s a lot of ‘probably’ – confirmation of life elsewhere in the solar system will require unconditional evidence.