Long, twisting tentacles of ice reaching into the rings around Saturn have been traced to their source, astronomers say, who point to icy water geysers on the ringed planet's moon, Enceladus.
Discovered by NASA's Cassini spacecraft in 2005, the geysers spew a mixture of water vapor, ice particles and simple organic compounds from the moon's surface.
Images from Cassini have revealed faint, sinuous plumes of icy material that reach from the surface of Enceladus into Saturn's E ring — in which the moon orbits — stretching tens of thousands of miles away from the moon itself, the researchers say.
They used computer simulations to recreate the trajectories ice grains would take after being ejected from individual geysers.
"We've been able to show that each unique tendril structure can be reproduced by particular sets of geysers on the moon's surface," says Colin Mitchell, a Cassini imaging team member at the Space Science Institute in Boulder, Colorado, and one of the authors of a study appearing in the Astronomical Journal.
Astronomers have long suspected the geysers on Enceladus supply material for Saturn's E ring, but this marks the first time the long trails of ice have been traced back directly to sources on the moon's surface.
Measurements of the size of most of the particles making up the E ring correspond to the size of the particles making up most of the Enceladus plumes, the researchers say, although variations in particle sizes are thought to correspond to different shapes seen in the icy tendrils.
In studying the Cassini images, the researchers were struck by how quickly the appearance and shape of the ice tendrils could change.
"It became clear to us that some features disappeared from one image to the next," said John Weiss, a Cassini imaging team member and co-author of the study.
It's likely because of tidal stresses, they suggest, the constant stretching and squeezing of Enceladus during its orbits around giant Saturn.
Such stresses could change the width of the surface fractures out of which geysers erupt, they explain, acting like an adjustable "nozzle" affecting the amount of material being ejected.
Enceledus is one of the solar system's prime models for scientists looking for possible extraterrestrial habitable zones on distant exoplanets, so it will be a major focus of the final years of the Cassini mission, NASA says.
At around 300 miles across, Enceladus is the sixth-largest moon of Saturn.
