In doing a recent flyby, Cassini gathered data which enabled researchers to confirm the gravitational pull of a large body of water.
"The measurements that we have done are consistent with the existence of a large water reservoir about the size (volume) of Lake Superior in North America," Professor Luciano Iess told BBC News. Professor Iess is an astronomer at the Sapienza University of Rome.
Scientists first came to suspect the moon might host a body of water when, in 2005, Cassini picked up on small diffusions of icy vapors escaping from cracks in the surface of Enceladus's south pole.
Like Iess, Professor Andrew Coates, a researcher at UCL-Mullard Space Science Laboratory in Surrey, England, thinks Enceladus might be one of the closest and most likeliest places to find life beyond Earth.
"I think Enceladus has gone to the top of the charts in terms of a place where there could be life," Coates said. "It's got several of the things which you need for life -- there's certainly the presence of heat, there's liquid water in this ocean, there's organics and that type of chemistry going on."
He added: "The only question is, has there been enough time for life to develop?"