Saturn’s moon Enceladus may have liquid water hidden away at its South Pole. Or so say NASA’s Cassini, the spacecraft dedicated to map out different aspects of the beautiful planet Saturn.
Enceladus is a tiny moon of Saturn, barely measuring 500km across. It’s been a curious object for many years, since it shone brightly in reflected sunlight, the surface being covered by a white layer of water-ice (meaning, frozen water). The surface is fractured into various patterns, indicating erosion in the past. Much of the surface is cratered; objects, mostly small rocky bodies, pulled in by Saturn’s gravity slam into Enceladus. A spectacular display is seen at the South Pole of the moon, where giant plumes of liquid and gaseous water rise, after penetrating the fractured surface. These shine in the Sun’s rays and also provide material to Saturn’s E-ring.
How Cassini Discovered Water
Cassini has made several flybys past Enceladus, in 2010 and in 2012, mapping its surface in great detail as it flew less than 100 km from the surface. It has also mapped the gravitational field of the object and this is what led to the discovery of a possible liquid water reservoir right beneath the surface. During these flybys, the trajectory of Cassini changes slightly due to the gravitational field of the moon. Being a light object, Cassini is quite sensitive to local gravitational fields, and corrects its path accordingly. This means that one can use this information to map out the gravitational field of the moon. If there is a major concentration of mass, like a large mountain, we can feel a positive addition to the field, while a hollow will show up in a negative way.
Cassini, mapping the gravitational field in the South Pole of Enceladus, found that there was a mass deficit on the surface, but a large mass excess abut 30-40 km below the surface. This ‘subsurface anomaly’, meaning a deviation from the standard mass distribution found below the surface, is, ‘compatible with the presence of a regional subsurface sea’, says the paper on the subject.
The next obvious question is this: does this sea of liquid water harbour life? The answer is that we don’t know. For a long time, Jupiter’s Europa was a happy hunting ground for alien-hunters; this status might be usurped by Saturn’s tiny Enceladus. A good, though quite a bit technical, answer can be found in a paper co-authored by Carolyn Porco, head of the Cassini mission here. This, however, predates the recent Cassini discovery and hinges its arguments on the plumes of liquid water seen emerging from the South Pole.
A nice video on the subject by JPL and NASA can be found here: