Measurements from the Cassini spacecraft have found a body of liquid water the size of a great lake on Saturn’s moon Enceladus.

Speculations about the abundance of water on Enceladus have been ongoing since plumes were discovered jetting out of its south pole in 2005. Debates centered around whether the water jets were a local phenomenon, resulting from friction between surface ice, or proof of a large subsurface supply, such as a lake or ocean.

The latest evidence strongly indicates the existence of an ocean on Enceladus, and comes from multiple visual and gravitational inspections of the poles between 2010 and 2012. Visually, Cassini noted a one kilometer depression in the ice at the south pole. Less ice should imply less mass and therefore less gravity in that vicinity. At the same time, Cassini noted that more gravity was present in the region than could be accounted for by just ice, especially ice that wasn’t there. The best way to explain both the gravitational measurements and the depression was by the presence of a material denser than ice: namely, water.