The tumbling and irregularly shaped moon Hyperion rotates away from the
Cassini spacecraft in this movie taken during a distant encounter in Dec.
2005. A shadow closes over the large crater at bottom as the movie
progresses.
Hyperion (280 kilometers, or 174 miles across) is covered with closely
packed and deeply etched pits. The warming action of the Sun on water ice
lying beneath a darkened layer of surface material apparently has deepened
and exaggerated the depressions already created by impacts.
Cassini scientists now think that Hyperion’s unusual appearance can be
attributed to the fact that it has an unusually low density for such a large
object, giving it weak surface gravity and high porosity. These characteristics
help preserve the original shapes of Hyperion’s craters by limiting the amount
of impact ejecta coating the moon’s surface. Impactors tend to make craters
by compressing the surface material, rather than blasting it out. Further,
Hyperion’s weak gravity, and correspondingly low escape velocity, means
that what little ejecta is produced has a good chance of escaping the moon
altogether.
The movie was made from 40 images taken over about two hours as Cassini
sped past the icy moon. A still image is also available (see PIA07684).
The images were taken in visible light with the Cassini spacecraft
narrow-angle camera on Dec. 23, 2005 at distances ranging from 228,000
kilometers (142,000 miles) to 238,000 kilometers (148,000 miles) from
Hyperion and at a Sun-Hyperion-spacecraft, or phase, angle ranging from 77
to 86 degrees. Resolution in the original images was about 1.4 kilometers
(0.9 mile) per pixel. The images have been magnified by a factor of two
and contrast-enhanced to aid visibility.
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.
For more information about the Cassini-Huygens mission visit
http://saturn.jpl.nasa.gov. The Cassini imaging team homepage is at
http://ciclops.org.
Note: The size of the Full-Res TIFF for the still image is 610 samples x 610 lines.
