Fractures on the surface of Enceladus record a long and complex history of
tectonic activity. Many of the geologically youngest fractures define
remarkably systematic patterns relative to Enceladus' axis of rotation,
as well as to its tidal orientation (that is, the longitudes that point
toward and away from Saturn).
These fracture patterns offer clues to global changes of shape that the
satellite has undergone over time, possibly in response to tidal forces
exerted by Saturn or as a result of changes in the internal structure of
the icy moon. Some of the most prominent global patterns of fracture are
delineated in color in the southern hemisphere map shown here. This map is
being released along with a northern polar projection map (See PIA07721).
This map is a polar stereographic projection that was mosaicked from the
best-available Cassini and Voyager clear-filter images. The map is
centered on the south pole and coverage extends to the equator. Gridlines
show latitude and longitude in 30-degree increments. The same maps are
available without colored fracture lines (see PIA07719 and PIA07720).
Terrain near the north pole (PIA07721) is among the most heavily cratered
and oldest on the surface of Enceladus. The conspicuously fractured
southern polar region is nearly devoid of impact craters, making this
terrain among the youngest on the moon's surface.
A unique feature of the south polar terrains is that broad networks of
folded or kinked fractures can be found throughout the region. A prominent
"chain" of these fractures (marked in red in the south polar map) abruptly
separates the youthful south polar terrains from the older terrains that
lie closer to the equator and appears to encircle the south pole near
about 55-degrees south latitude.
The wavy boundary of the south polar terrain is interrupted in numerous
places by Y-shaped, or funnel-shaped, discontinuities that curve and
taper northward. Well-developed examples of the funnel-shaped
discontinuities appear to transition to systems of north-south trending
surface cracks (marked in blue).
These north-south trending cracks are best explained as if they formed in
response to tension stresses that are parallel to lines of latitude. Such
extensional "hoop stresses" would be expected to develop if the equator
became wider, perhaps in response to a change in the moon's spin rate.
Globally systematic patterns of fracture on Enceladus occur in ancient,
cratered terrain as well as youthful terrain. Shown in green on the maps
-- and particularly apparent in the northern hemisphere projection -- are
roughly orthogonal (or perpendicular) systems of north-south and east-west
trending fractures that formed quite close to the tidal axis of Enceladus.
The moon's tidal axis is a line extending from 0-degrees longitude to
180-degrees longitude. Such orthogonal fractures might have formed in
response to tidal stresses exerted on Enceladus by Saturn.
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 was designed, developed and assembled at JPL.
For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov.
For additional images visit the Cassini imaging team homepage http://ciclops.org.