This collage, consisting of two Cassini images
of long, sinuous, tendril-like features from Saturn's moon Enceladus and
two corresponding computer simulations of the same, illustrates how
well the structures, and the sizes of the particles composing them, can
be modeled by tracing the trajectories of tiny, icy grains ejected from
Enceladus' south polar geysers. Credit: NASA/JPL-Caltech/Space Science
Institute. › Full image and caption
This graphic plots the source locations of the geysers scientists have
located on Enceladus' south polar terrain. Credit:
NASA/JPL-Caltech/Space Science Institute. › Full image and caption
Long, sinuous, 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.
This result is published online today in a study in the Astronomical
Journal, along with additional insights into the nature of the
structures.
"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
Colin Mitchell, a Cassini imaging team associate at the Space Science
Institute in Boulder, Colorado, and lead author of the paper. Mitchell
and 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.
Under certain lighting conditions, Cassini's wide-view images showing
icy material erupting from Enceladus reveal faint, finger-like
features, dubbed "tendrils" by the imaging team. The tendrils reach into
Saturn's E ring -- the ring in which Enceladus orbits -- extending tens
of thousands of miles (or kilometers) away from the moon. Since the
tendrils were discovered, scientists have thought they were the result
of the moon's geysering activity and the means by which Enceladus
supplies material to the E ring. But the ghostly features had never
before been traced directly to geysers on the surface.
Because the team was able to show that tendril structures of
different shapes correspond to different sizes of geyser particles, the
team was 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 John Weiss, an imaging
team associate at Saint Martin's University in Lacey, Washington, and an
author on the paper.
The authors suspect that changes in the tendrils' appearance likely
result from the cycle of tidal stresses -- squeezing and stretching of
the moon as it orbits Saturn -- and its control of the widths of
fractures from which the geysers erupt. 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.
There is even more that can be extracted from the images, the
scientists say. "As the supply lanes for Saturn's E ring, the tendrils
give us a way to ascertain how much mass is leaving Enceladus and making
its way into Saturn orbit," said Carolyn Porco, team leader for the
imaging experiment and a coauthor on the paper. "So, another important
step is to determine how much mass is involved, and thus estimate how
much longer the moon's sub-surface ocean may last." An estimate of the
lifetime of the ocean is important in understanding the evolution of
Enceladus over long timescales.
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 Cassini-Huygens mission is a cooperative project of NASA, ESA
(European Space Agency) and the Italian Space Agency. NASA's Jet
Propulsion Laboratory in Pasadena, California, manages the mission for
the agency's Science Mission Directorate in Washington. JPL is a
division of the California Institute of Technology in Pasadena. The
Cassini imaging operations center is based at the Space Science
Institute in Boulder, Colo.
New images released today can be found at: http://www.ciclops.org/view_event/205
Media Contact
Preston Dyches
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-7013
preston.dyches@jpl.nasa.gov
Steve Mullins
Space Science Institute, Boulder, Colo.
720-974-5859
media@ciclops.org
Source: JPL-Caltech/News
