14 DAY TRIAL // Jets of fine, icy particles streaming from Saturn's moon Enceladus were captured in recent images from NASA's Cassini spacecraft. The images provide unambiguous visual evidence that the moon is geologically active.
"For planetary explorers like us, there is little that can compare to the sighting of activity on another solar system body," said Dr. Carolyn Porco, Cassini imaging team leader.
The Cassini images clearly show multiple jets emanating from the moon's South polar region. Based on earlier data, scientists strongly suspected these jets arise from warm fractures, known as "tiger stripes".
The fainter, extended plume stretches at least 186 kilometers above the surface of Enceladus. Cassini flew through the plume in July, when it passed a few hundred kilometers above the moon. During that flyby, Cassini's instruments measured the plume's constituent water vapor and icy particles.
The recent images were part of a sequence planned to confirm the presence of the plumes and examine them in finer detail.
"I think what we're seeing are ice particles in jets of water vapor that emanate from pressurized vents. To form the particles and carry them aloft, the vapor must have a certain density, and that implies surprisingly warm temperatures for a cold body like Enceladus," imaging team member Dr. Andrew Ingersoll said.
"In some ways, Enceladus resembles a huge comet. Only, in the case of Enceladus, the energy source for the geyser-like activity is believed to be due to internal heating by perhaps radioactivity and tides rather than the sunlight which causes cometary jets," Dr. Torrence Johnson said.
The heating resulted from the tides caused by the gravity forces is similar to that resulted from repeatedly squeezing a rubber ball.