Recent images taken by the spacecraft show streams of fine, icy particles rising from the moon's south pole, suggesting they originated from warm zones in the region.

The discovery puts Enceladus in the class of geologically active moons with Jupiter's Io and Neptune's Triton.

It's unclear what causes the geologic activity, but scientists think it's due to internal heating caused by radioactivity or tides.

Cassini passed through the plume stretching up to 300 miles above Enceladus' surface in July. During that flyby, instruments aboard the spacecraft measured the plume's makeup and found water vapor and icy particles.

"This has been a heart-stopper, and surely one of our most thrilling results,'' Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, Colo., said in a statement.

Results were presented Tuesday at an American Geophysical Union meeting in San Francisco.

The Cassini-Huygens mission is a joint NASA-European Space Agency project. The combined craft was launched in 1997 and arrived in orbit around Saturn last year. Huygens, a probe developed and controlled by the ESA, touched down on the giant moon Titan earlier this year.