A fine spray of small, icy particles emanating from the warm, geologically unique province surrounding the south pole of Saturn's moon Enceladus was observed in a Cassini narrow-angle camera image of the crescent moon taken on Jan. 16, 2005.
Taken from a high-phase angle of 148 degrees -- a viewing geometry in which small particles become much easier to see -- the plume of material becomes more apparent in images processed to enhance faint signals.
Imaging scientists have measured the light scattered by the plume's particles to determine their abundance and fall-off with height. Though the measurements of particle abundance are more certain within 100 kilometers (60 miles) of the surface, the values measured there are roughly consistent with the abundance of water ice particles measured by other Cassini instruments (reported in September, 2005) at altitudes as high as 400 kilometers (250 miles) above the surface.
Imaging scientists, as reported in the journal Science on March 10, 2006, believe that the jets are geysers erupting from pressurized subsurface reservoirs of liquid water above 273 degrees Kelvin (0 degrees Celsius).
The image at the left was taken in visible green light. A dark mask was applied to the moon's bright limb in order to make the plume feature easier to see.
The image at the right has been color-coded to make faint signals in the plume more apparent. Images of other satellites (such as Tethys and Mimas) taken in the last 10 months from similar lighting and viewing geometries, and with identical camera parameters as this one, were closely examined to demonstrate that the plume towering above Enceladus' south pole is real and not a camera artifact.
The images were acquired at a distance of about 209,400 kilometers (130,100 miles) from Enceladus. Image scale is about 1 kilometer (0.6 mile) per pixel.
This caption was updated on March 9, 2006.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.
Credit: NASA/JPL/Space Science Institute