Spongy-Looking Hyperion Tumbles Into View

PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov

Guy Webster (818) 354-6278
Jet Propulsion Laboratory, Pasadena, Calif.

Preston Dyches (720) 974-5859
Cassini Imaging Central Laboratory for Operations
Space Science Institute, Boulder, Colo.

Image Advisory: 2005-114 July 11, 2005

Spongy-Looking Hyperion Tumbles Into View

Two new Cassini views of Saturn's tumbling moon Hyperion offer
the best looks yet at one of the icy, irregularly-shaped moons
that orbit the giant, ringed planet.

The image products released today include a movie sequence and
a 3D view, and are available at http://saturn.jpl.nasa.gov,
http://www.nasa.gov/cassini and http://ciclops.org .

The views were acquired between June 9 and June 11, 2005,
during Cassini's first brush with Hyperion.

Hyperion is decidedly non-spherical and its unusual shape is
easy to see in the movie, which was acquired over the course of
two and a half days. Jagged outlines visible on the moon's
surface are indicators of large impacts that have chipped away
at its shape like a sculptor.

Preliminary estimates of its density show that Hyperion is only
about 60 percent as dense as solid water ice, indicating that
much of its interior (40 percent or more) must be empty space.
This makes the moon more like an icy rubble pile than a solid
body.

In both the movie and the 3D image, craters are visible on the
moon's surface down to the limit of resolution, about 1 kilometer
(0.6 mile) per pixel. The fresh appearance of most of these
craters, combined with their high spatial density, makes Hyperion
look something like a sponge.

The moon's spongy-looking exterior is an interesting coincidence,
as much of Hyperion's interior appears to consist of voids.
Hyperion is close to the size limit where, like a child compacting
a snowball, internal pressure due to the moon's own gravity will
begin to crush weak materials like ice, closing pore spaces and
eventually creating a more nearly spherical shape.

The images used to create these views were obtained with Cassini's
narrow-angle camera at distances ranging from approximately 815,000
to 168,000 kilometers (506,000 to 104,000 miles) from Hyperion.
Cassini will fly within 510 kilometers (317 miles) of Hyperion on
Sept. 26, 2005.

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 Cassini-Huygens 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 team is based at the Space Science
Institute, Boulder, Colo.

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