Long, tendril-like structures seen in the vicinity of Saturn's icy moon Enceladus originate directly from geysers erupting from its surface, according to scientists studying images from NASA's Cassini spacecraft.
"We've been able to show that each unique tendril structure can be reproduced by particular sets of geysers on the moon's surface," said lead author Colin Mitchell, a Cassini imaging team associate at the Space Science Institute in Boulder, Colo., according to a press release. Mitchell and his colleagues used computer simulations to follow the trajectories of ice grains ejected from individual geysers. The geysers, which were discovered by Cassini in 2005, are jets of tiny water ice particles, water vapor and simple organic compounds.
Because the team was able to show that tendril structures of different shapes correspond to different sizes of geyser particles, they were able to zero in on the sizes of the particles forming them. They found the tendrils are composed of particles with diameters no smaller than about a hundred thousandth of an inch, a size consistent with the measurements of E-ring particles made by other Cassini instruments.
As the researchers examined images from different times and positions around Saturn, they also found that the detailed appearance of the tendrils changes over time. "It became clear to us that some features disappeared from one image to the next," said study author John Weiss, an imaging team associate at Saint Martin's University in Lacey, Wash., according to the press release.
The authors suspect that changes in the tendrils' appearance likely result from the cycle of tidal stresses - the squeezing and stretching of the moon as it orbits Saturn. The stronger the tidal stresses raised by Saturn at any point on the fractures, the wider the fracture opening and the greater the eruption of material. The authors will investigate in future work whether this theory explains the tendrils' changing appearance.
Because of its significance to the investigation of possible extraterrestrial habitable zones, Enceladus is a major target of investigation for the final years of the Cassini mission. Many observations, including imaging of the plume and tendril features, and thermal observations of the surface of its south polar geyser basin, are planned during the next couple of years.
The results are published in a study in the Astronomical Journal.