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

[Ron Baalke]

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.

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