[meteorite-list] Cassini's Doubleheader Flybys Score Home Run

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Sep 30 14:38:21 2005
Message-ID: <200509301837.j8UIb6s06905_at_zagami.jpl.nasa.gov>

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

Carolina Martinez (818) 354-9382
Jet Propulsion Laboratory, Pasadena, Calif.

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

Image Advisory: 2005-158 September 30, 2005

Cassini's Doubleheader Flybys Score Home Run

Cassini performed back-to-back flybys of Saturn moons Tethys
and Hyperion last weekend, coming closer than ever before to
each of them. Tethys has a scarred, ancient surface, while
Hyperion is a strange, spongy-looking body with dark-floored
craters that speckle its surface.

New images, mosaics and a movie of these bodies are available
at http://saturn.jpl.nasa.gov , http://www.nasa.gov/cassini
and http://ciclops.org .

Images of Tethys taken during Cassini's close approach to the
moon on Sept. 24, 2005, reveal an icy land of steep cliffs and
craters. Cassini photographed the moon's south pole, a region
not seen by NASA's Voyager spacecraft.

A giant rift called Ithaca Chasma cuts across the disk of Tethys.
Much of the topography in this region, including that of Ithaca
Chasma, has been thoroughly hammered by impacts. This
appearance suggests that the event that created Ithaca Chasma
happened very long ago. Near a prominent peaked crater named
Telemachus are the remnants of a very old crater named
Teiresias. The ancient impact site is badly overprinted and
eroded by impact weathering and degradation. All that remains
is a circular pattern of hummocks that mark where the old crater
rim existed. Many of the fresh-appearing craters exhibit
unusually bright crater floors, in contrast to the dark-floored
craters seen on Saturn's oddly tumbling moon Hyperion.

Images of Hyperion taken on Sept. 26 show a surface dotted with
craters and modified by some process, not yet understood, to
create a strange, "spongy" appearance, unlike the surface of any
other Saturn moon.

A false-color image of Hyperion reveals crisp details and
variations in color across the strange surface that might
represent differences in the composition of materials. Hyperion
has a notably reddish tint when viewed in natural color.

Scientists are extremely curious to learn what the dark material
is that fills many craters on this moon. Features within the
dark terrain, including a 200-meter-wide (650-feet) impact
crater surrounded by rays and numerous bright-rimmed craters,
indicate that the dark material may be only tens of meters thick
with brighter material beneath.

Scientists will also be examining Cassini's sharp views in hopes
of determining whether there have been multiple episodes of
landslides on Hyperion. Such "downslope" movement is evident
in the filling of craters with debris and the near elimination
of many craters along the steeper slopes. Answers to these
questions may help solve the mystery of why this object has
evolved different surface forms from other moons of Saturn.

Cassini flew by Hyperion at a distance of only 500 kilometers
(310 miles). Hyperion is 266 kilometers (165 miles) across,
has an irregular shape, and spins in a chaotic rotation. Much of
its interior is empty space, explaining why scientists call
Hyperion a rubble-pile moon. This flyby was Cassini's only
close encounter with Hyperion in the prime mission four-year
tour. Over the next few months, scientists will study the
data in more detail.

Cassini flew by Tethys at a distance of approximately 1,500
kilometers (930 miles) above the surface. Tethys is 1,071
kilometers (665 miles) across and will be visited again by
Cassini in the summer of 2007.

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.

-end-
Received on Fri 30 Sep 2005 02:37:06 PM PDT


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